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PLANNING A NATIVE PLANT PROJECT
Once a decision has been reached to use native plants in landscaping or in a restoration project, there are a number of important factors that should be considered. In order to have a successful project, these factors should be examined during the planning process long before plants are brought onto the site.
It is very important to consider carefully the time it will take to implement the project. Working with plants creates specific needs because certain phases of a project can only be done at certain times of the year. Lack of foresight in this area can be disastrous. The first section on Establishing a Realistic Timeframe explains some of the features of native plant projects that require proper timing in order to develop an effective project. It is also helpful, when beginning to plan the project, to have a clear idea of the project goals and objectives. Information on doing so can be found in the section on Determining Project Targets. After setting goals, take the time to understand the planting site thoroughly with the aim of anticipating and addressing possible problems as outlined in the section on Evaluating The Site. Finally, good planning will entail carefully deliberated decisions on what native plants will be used and where or how they will be acquired. There are a number of sections following Evaluating The Site that can help in completing that phase of the project.
While the following sections are mainly intended as a guide for native plant restoration projects, many of the same concepts apply to using native plants in landscaping. Consequently, there is useful information in this guide for anyone who is planning to use native plants.
Establishing a Realistic Timeframe
Native plant restoration projects must be planned well in advance. It is not practical for most projects to begin in January and expect to install plants in the ground in March or April. There is much that needs to happen between the time that the project is identified and the time the plants are ready to go into the ground.
Taking time at the beginning to thoroughly evaluate the site and develop a well-thought out site preparation and planting plan is an important first step to planning a successful project. This may require evaluating the site during different seasons to understand how the site changes over time. Also, identifying a natural model or referencing a preserve can add relevant information. This understanding will help in avoiding costly mistakes such as planting plants in a place where they cannot survive the environmental conditions.
Using native plants in a restoration project often involves the collection of locally-adapted plant material or commercially grown local ecotypes. Materials are often not immediately available in the quantities and quality required from native plant suppliers. If this is the case, make sure there is enough lead time to collect and propagate the plant material required - either using project staff or contracting with a supplier. The only time this might not be the case is if there is already a high demand for the native plants needed and the native plant suppliers have accurately anticipated that demand. Advanced planning and ordering of the plant material will ensure the availability of desired species with proper hardening of the stock or harvesting of the seed.
If seeds are to be collected there is usually only a short window during the year when seeds are ripe and available for collection. Often, a series of collections is needed to reflect the diversity of the seasons. After the seeds are collected, some require special treatment, such as several months of cold hardening or after-ripening, before they will germinate. If plants need to be propagated from plant cuttings, a general rule of thumb is to allow 18-30 months from the time the parent plants are located in the summer to the time rooted cuttings are of sufficient size to survive transplantation into the restoration site. To be absolutely sure of plant availability, containerized seedlings should be ordered 1-2 years prior to planting and bareroot seedlings should be ordered 2-4 years prior to planting (Colorado Department of Natural Resources 1998). Commercially grown seed also requires ordering ahead of time.
Involving local experts in the design and development of the restoration project will also require advance planning. Assistance might be needed from experts in several fields, such as hydrology, geology, soil science, horticulture, biology, and wetland ecology. Coordinating among numerous people always requires more time than originally expected.
Although it may seem more economical to coordinate a native plant project on a shorter time schedule, usually the results will not be very good. In order to ensure the greatest long-term success of the project, it is well worth investing time at the beginning to evaluate the site and to ensure that all the plants or seeds needed for the project can be obtained.
Determining Project Targets
When starting a native plant restoration project it is important to clearly determine the project targets.
Defining the Problem
The first question to answer is: what are the problems with the site? Is the problem soil erosion due to a lack of vegetation, low native biodiversity due to a near monoculture of one or two invasive weeds, increased flooding problems due to a reduction in the ability of the ecosystem to regulate water flow or some other problem related to vegetation? Asking specific questions and considering all aspects are essential to identifying problems at the site.
Setting Goals and Objectives
Once the site's problems have been identified, it is easier to set clear goals and objectives. A goal is more overarching and an objective is more specific. Setting clear goals and objectives will help in making good decisions as the planning process continues. Clear goals and objectives are also essential for defining a monitoring plan that will quantitatively evaluate the long-term success of the project. Each objective should relate to some measurable criterium.
Some examples of goals, related objectives and measurable criteria:
Goal: increase available wildlife habitat
Objective: plant native plants that can provide food for local wildlife
Measurable Criterium: establish greater than 50% cover of native plant species that are providing food for wildlife
Goal: improve water quality
Objective: plant native species that require less fertilizers and pesticides than non-native plants, reducing chemical run-off into local streams
Measurable Criterium: reduce the quantity of commercial fertilizers used on site by 90%
Goal: reduce soil erosion
Objective: plant native species that will develop strong extensive root structures to hold soil in place
Measurable Criterium: reduce soil loss to less than 5 Mg/ha per year
With careful planning, the project can address multiple goals. Ideally, a project should aim for a holistic approach toward solving multiple problems by reaching several goals rather than a result benefiting a single goal.
Evaluating the Site
The site condition is a critical factor in the success of a restoration project. Plants that are ill suited to a site's growing conditions will have difficulty surviving. Consequently, the conditions of the site need to be known before making a detailed restoration plan. Remember also that the site can look very different at different times of the year. It may be completely dry in the summer, but look like a pond in the winter. Try to evaluate the site during all seasons or find out from others that are familiar with the site how it might change over the course of a year.
Important characteristics to consider include the following:
- history of residual herbicides and/or pesticides
- existing ecological communities
- presence of exotic plant species
- abundance or lack of native plant species
- climate and microclimate
- frost-killing dates
Ideally, the assistance of specialists such as soil scientists or hydrologists should be obtained to evaluate some of these characteristics in order to make a more accurate determination of the existing site conditions.
Soils are one of the most important factors that can influence plant survival on the site. A few of the major characteristics of soil and examples of how they can affect plant health and survival are listed below.
- texture - affects moisture levels and nutrient exchange
- pH - affects the ability of plants to take up nutrients
- organic matter - affects nutrient and moisture availability
- compaction - makes it difficult for plant roots to penetrate the soil; affects nutrient cycles & beneficial organisms
- residual herbicides or pesticides - can affect plants and associated insects
For general soils information contact the local Natural Resources Conservation Service (NRCS) office or the local Conservation District. Referring to the published soil survey for the site's area will be an important first step. Some soils information can also be found on-line at the National Soil Survey Center's web site at http://soils.usda.gov/.
In evaluating specific project site soils, having a professional soil scientist provide assistance would be the preferred course of action. If there are none on the project team, try contacting NRCS, the county Cooperative Extension office of the state's land grant university or an environmental consulting firm. However, there are also a few things that can be done without a soil scientist on staff to get a basic idea about the type of soil on the site
The first step in examining the soils at the site is to collect some soil samples. The method of collection for soil samples can affect the results of tests, so it is important to consider a few basic collection guidelines. Soil samples are usually collected with some type of soil probe that can collect a core cylinder sample of soil. These soil probes can be purchased through most forestry or agronomic supply catalogs (Appendix A).
The recommended depth of the sample is variable depending on the type of site and the type of analysis. It is best to get the advice of a soil scientist. However, if an expert opinion is not available, samples are often collected to a depth of around 20 centimeters. Deeper samples are often obtained if woody plants are part of the restoration project.
Sampling location should also be considered carefully. Samples should be taken at a number of different places in the site in order to determine soil variability. Composite samples consist of a minimum of three soil cores from a single area to get a representative sample. While agronomists traditionally composite samples, an understanding of the heterogeneity of both disturbed areas and reference areas is very important for predicting the desired result or likelihood of success of the project. When sending in non-composite samples, indicate to the lab that field replicates instead of composites are being submitted. Try and sample areas that may have different soil types. Different soil types can be indicated if the vegetation is varied from one location to another and if the water relationships are different from one part of the site to another. If the soil chemistry or texture is different in different parts of the site, that is an important factor that will need to be considered during site preparation and the planting design phase.
If samples will be stored or transported before doing a chemical analysis (pH, organic matter, or nutrients), they should be placed in a plastic bag at the site, closed with a ziplock or a twist tie, labeled with a permanent marker, and kept cool during transport. After transport most samples should immediately be air-dried by spreading out each soil sample into a thin layer on separate labeled pieces of clean butcher paper. However, certain tests, such as those for plant-available nitrogen, require fresh samples to be processed as soon as possible after collection, so the lab should be consulted beforehand.
If the services of a soil testing laboratory are to be used, be sure to talk to them about their specific guidelines for sample collection. It is also important to let them know that the soil is from a disturbed area. In most cases, these labs run tests and interpret results for farmers. Tests results will be interpreted differently if viewed in the context of a disturbed area rather than an agricultural area.
The following characteristics of soil are considered a part of good project planning.
Soil texture is important because it influences both water availability and nutrient availability. For a rough idea of the texture, moisten the soil a little and then feel the texture by rubbing and rolling some of it between fingers. Is it very sandy and not able to stick together much or is it mostly fine material that can be molded like clay? Clay-dominated soils will also tend to stain skin whereas sandy or silty soils will rub off more easily. Soils that are very sandy tend to be drier because they allow water to drain quickly. Clay-dominated soils are often associated with wetlands because of their poor drainage.
The soil pH has a major effect on nutrient availability. Test the soil pH using the following steps:
- Use a 2 mm sieve to remove all soil particles greater than 2 mm.
- Mix approximately 20 to 25 grams of the sieved soil with a 1:1 or 2:1 ratio of water to soil to make the soil into a wet paste. Add just enough water to saturate the soil (when forming a depression in the sample, water just begins to move into the hole and puddle).
- Let the paste sit for half an hour to equilibrate.
- Stir the paste again.
- Measure the pH of the paste with a pH meter or pH paper.
Make sure a several different samples from different places at the site are tested to be sure of accuracy and that the pH does not vary throughout the site. The range of pH values is from 0 to 12. The classification of the pH of soils is:
|strongly acid soils|
5 - 6.5
|moderately acid soils|
7 - 8.5
|or higher strongly alkaline soils|
Knowing the pH will help guide plant selection as certain plants prefer more acid soil conditions and others prefer more alkaline soil conditions. If the site has elevated concentrations of heavy metals, it will be necessary to keep the soil pH greater than seven for the restoration program to be successful. This can be accomplished through limestone application.
Salt concentration of the soil is measured using a conductivity meter. These are similar to pH meters and are easily used. Generally, an electrical conductivity measurement of greater than 2 deciSiemans per meter is an indication of a potential salt problem.
Organic matter is typically defined as a combination of recognizable organic material (roots, insects, etc.) and decayed organic material that is no longer recognizable (humus) in the soil. The terms "duff" and "litter" are also used in some literature and by some resource managers. There are a number of beneficial effects of organic matter in the soil, including increased water holding capacity and increased nutrient exchange.
There are a few field methods for detecting organic matter which do not require an intricate setup. However, these do not produce accurate assessments or estimates. They include:
- Visual assessment - dark color of soil
- Floating - floating off organic matter by shaking a soil sample in a jar of water
Soil organic matter can be estimates using a muffle furnace that can heat soil to very high temperatures. Follow these steps to determine the soil organic matter content:
- Use a 2 mm sieve to remove all soil particles greater than 2 mm.
- Dry the soil sample at 105°C overnight.
- Weigh the sample and record its weight. This is the initial dry weight.
- Burn the sample in the muffle furnace at 450°C for four and a half hours.
- Weigh the sample and record its weight again. This is its final weight.
- Calculate the percentage of organic matter in the soil using the following equation:
|x 100 = % organic matter|
The typical range of organic matter percentages ranges from trace amounts in sandy desert soil to up to 20 or 30 percent in some forest soils. Organic soils with greater than 30 percent organic matter, such as peat, are mainly found in wetlands or former wetlands.
The estimation of percent organic matter can sometimes be an indicator of nutrient availability in the soil. However, having a professional soil lab test the soil for available nutrients will be a more accurate determination. This information can be used to check if appropriate nutrient amounts are available for the desired plant community. It is also important to find out what the organic matter content is in nearby soils that have not been disturbed. This can be done by consulting the local NRCS office or the soils testing lab of the state's land grant university. These places would also be a good place to ask about sources of organic matter should the site require additional material. If the soil has lower total organic matter than comparable nearby soils, adding organic matter to the soil will improve the chances for success in plant restoration.
Another soil characteristic to consider is soil compaction, especially if the site has previously been subjected to a lot of heavy traffic (vehicular, livestock, bicycle, foot). Compacted soil can make it difficult for plant roots to penetrate, thus decreasing their ability to grow and survive. Just trying to dig in the soil gives a rough idea of the compacted level. Soils with higher clay contents tend to become compacted much more easily than soils with high sand and silt contents. However, a more quantitative way to evaluate soil compaction is to measure the bulk density of the soil. There are bulk density soil samplers, also called core soil samplers, available through forestry supply catalogs (Appendix A) that can be used to collect a known volume of soil. However, as long as a known volume of soil is collected it need not involve a bulk density sampler. One alternative to a bulk density sampler is to collect a sample, then place a waterproof plastic bag in the hole left by collection, fill the bag with water until the level is at the same level as the soil surface with the bag pressed against the sides of the hole, and the water is poured into a graduated cylinder to measure its volume. The soil sample should then undergo the following steps.
- Carefully collect a soil sample of a known volume.
- Dry the soil in a 105°C oven to remove any moisture.
- Weigh the dried soil sample.
- Use the following equation to calculate bulk density:
dried soil weight / known original volume of sample = bulk density
The point at which the soil becomes compacted enough to impact root growth is a bulk density of 1.6 Mg/m^3. If bulk density is too high, a good way to decrease it and improve the growth environment for plants is to incorporate organic matter into the soil. Addition of manure, composts or municipal biosolids will improve soil aggregation and decrease bulk density, but may also add significantly to problems with invasive plants. For more information on the use of these type of amendments see the separate paper on Using Biosolids for Reclamation and Remediation of Disturbed Soils.
Another good way to get more information about the soils at the site is to find the Soil Survey reports for the area. These can often be obtained through the local NRCS office, cooperative extension offices, libraries or city or county planning departments. Maps in the soil survey can cover the classification of the site soils and usually will include a detailed description of the characteristics of that soil.
The topography of a site can also play an important role in restoration design. For example, steep slopes are more likely to have soil erosion problems and low areas are more likely to be inundated with water for part of the year. Topography can be assessed a number of ways including visual inspection, use of survey equipment, aerial photographs, and U.S. Geological Survey quadrangle maps.
When restoring a wetland, this aspect should be paid close attention. Many wetland plants are only successful at very specific microelevations with respect to a wetland because they tolerate only certain levels of water inundation. Planting them at the wrong microelevation, where they might receive too much or too little water, could result in a considerable amount of plant loss.
Steep slopes greater than 2:1 may require the addition of erosion control materials such as matting, weed-free straw or mulch. A local soil scientist should be able to assist with selecting appropriate solutions.
As stated above, different plants prefer different levels of moisture. The hydrology of the site will determine the amount of water available to plants at different times of the year. Consequently, the choice of native plant species and the locations for planting should be heavily influenced by the hydrology at the site.
The information about soil types as outlined in the soils section will begin to suggest something about the typical hydrology of the site. Soils that are fine textured and classified by the soil survey as "hydric" soils are typically associated with wetlands, and the site should be expected to be flooded at least seasonally. Other factors to assess when doing a hydrologic survey are the locations of any springs or streams, depth to groundwater, the amount of rainfall or snowmelt that the site receives, any type of periodic flooding events, and any disturbances of the historical hydrologic regime.
For more help with finding hydrologic information about the project site, try contacting the local U.S. Geological Survey's Water Resources Division Office. Visit their website (http://water.usgs.gov) and go to the local information section to find the local contact. If they don't have the information needed, then they can probably offer good advice on where to get assistance. The website also has some good information available on topics such as stream flows and water quality that may be relevant.
If dealing with a complicated hydrologic site such as a wetland, it would be wise to hire a professional hydrologist to conduct an assessment of the site. While important in any restoration project, understanding the hydrology is especially critical in wetland ecosystem restoration. Many wetland plants must be planted in very specific places according to the hydrology of the system and will die if planted in the wrong place. It may be important to restore site hydrology before plantings can be successful.
Existing Ecological Communities
Knowing what is already living on the site can help predict what species are likely to succeed on the site and what potential problems may need to be addressed before native plants are reintroduced. If assistance is needed in identifying the plants on the site, there are a number of places that may be able to provide assistance in finding someone. These include the local conservation district office, the local office of the Natural Resources Conservation Service, the botany department of a local university, the county Cooperative Extension offices of land grant universities, the state Department of Natural Resources, the state Natural Heritage Program (Appendix A) or an environmental consulting firm.
Conducting an inventory of the plant species that are present on the site is useful for several reasons. First, if native plants are still found on part of the site, they are species that should probably be included in the restoration plan. The only exception to this would be if the rest of the site was very different in character from the place where natives were growing; in which case they would be unlikely to survive in the new area. Secondly, the inventory may find exotic species that are considered noxious weeds or invasive plants that can spread quickly and outcompete native species. These are species that should be removed or contained before new plants are planted. A third use of the inventory would be to identify any indicator species. Indicator species are plants that are known to prefer certain types of growing conditions such as wet soils, compacted soils, high nutrient levels or low light levels. Finding these types of species can help predict the probable growing conditions at the site. To find this information, consult the local flora or speak with a native plant expert in the area. Finally, having an idea of what is growing on the site is also a good indicator of what types of seeds are in the soil. This can be useful if there is the potential for a lot of native seeds to be present or can be a problem if there are a lot of weed seeds that could grow and reestablish themselves after the mature plants are removed. Prior to starting soil or herbicide impacts on prairie sites, conducting a prescribed burn on a site can sometimes rejuvenate suppressed native plants.
Making a list of native plant species that are found coming into old or new disturbances in the surrounding areas can be helpful. These native plants are the early colonizers and grow well in disturbances similar to the potential restoration site. They will eventually be replaced by the indicator species.
In addition to a plant survey, a wildlife survey can be useful to determine what is already present at the site. It can indicate what type of habitat already exists at the site and what kinds of habitat modifications might be useful to the wildlife already present. Be sure to include arthropods (insects and spiders) as they are excellent indicators of the site's biological health. Some wildlife can also play a crucial role in determining the success of a restoration project because of the potential for them to damage young plants that have not yet become established. Entire restoration projects have been destroyed in a day by geese pulling up and eating all the tender young shoots that were so carefully planted the day before. In other projects, rodents have caused many of the planted young trees to die because they gnaw on the bark at the base of the trunk. There are many ways to design a restoration project to minimize wildlife damage to new plants, such as fencing or tree protection bands. Knowing what potential wildlife problems are present can help in planning the type of protection needed.
When examining the ecological communities on the site, don't forget to look at the nearby ecological communities. There may be an intact native community nearby that could be used as a reference site as the restoration project is designed. When environmental conditions are similar, the reference site's inventory list may be used when defining the project site's species list. There may also be nearby areas with invasive plant species that could potentially invade the restoration site. If an important goal of the restoration is wildlife habitat, it will be important to look at the wildlife corridors that exist between the site and other natural areas. Good advice about where to get useful information on local wildlife can be obtained from the local office of the U.S. Fish and Wildlife Service (http://www.fws.gov/) or from the state's wildlife agency.
Disturbances play a very important role in shaping the ecological communities found on the landscape. Some communities are damaged by certain types of disturbances and other communities are dependent upon certain types of disturbances for their continued survival. One example of damage to a community caused by a disturbance is intensive grazing which favors species that can survive grazing pressures and eliminates those that are sensitive to grazing. Other consequences of detrimental disturbances include accelerated rates of erosion, loss of developed soil, declines or loss of nutrient cycling, and adverse impacts on natural hydrologic pathways. An example of a positive relationship between a community and disturbance are prairie communities that are dependent on fire. The periodic fires in the prairies kill off young invading woody species and create bare patches for new prairie seedlings to germinate and grow.
If a native plant community is to be reestablished on a degraded site, disturbance patterns that will harm these plants will need to be eliminated as much as possible and disturbance patterns that the community requires will need to be reinstated to the highest extent possible. Consequently, it is important to understand what types of disturbances have taken place in the past that may have affected the local community, what disturbances may take place in the future that could affect the ecological balance, and what disturbances may be necessary to maintain the desired ecological community.
Examples of types of disturbances include:
- chemical contamination
- fire or suppression of fire
- fragmentation and roads
- invasive species
- mechanical disturbance
- trampling and off road vehicle use
Climate and Microclimate
The general climate of the area and the specific microclimate of the restoration site are also important factors to consider. Both affect the water availability, amount of sunlight, and maximum and minimum temperatures each plant will experience. All of these factors will influence the ability of each plant to grow and survive.
Some general climate factors to consider:
- maximum and minimum temperatures (daily, monthly, yearly)
- number of frost-free days
- seasonality of precipitation (e.g. wet winters, dry summers)
- total average yearly precipitation
Some microclimate factors to consider:
- aspect of site (e.g., north-facing or south-facing)
- range of topography (e.g., small changes in elevation such as dips in the landscape)
- total pavement area or area of impervious surface nearby (which can increase local temperatures and amounts of surface water runoff)
To get a general sense of the local climate in the area of the site, visit the National Climactic Data Center's website (http://lwf.ncdc.noaa.gov/oa/ncdc.html). The site also has access which allows retrieval of specific weather history information for the weather data collection site nearest the project site (See Appendix A). This section allows the choosing of information parameters and which data site will be viewed, and then graphs the information for the years that data is available.
Choosing the Appropriate Plant Species
Once clear goals and objectives have been set for the project and a thorough site evaluation has been conducted, native plant species that will be appropriate for the site should be chosen. Choose native species that will match restoration site conditions by keeping in mind the three most important variables for plants: water, light, and nutrient availability. For instance if the site has sandy, well-drained soils and full exposure to the sun, it would not be a good idea to plant species that require moist, shady conditions. This may sound obvious, but a surprising number of native plant projects have made this kind of mistake.
In developing a plant list, remember that species are typically found together in certain groupings, referred to as plant associations or plant communities. These associations will suggest other plant species that may be appropriate. Planting species together based on their typical associations is a good idea because they will all be adapted to the same site conditions. They may also have symbiotic relationships, a relationship where each helps the other in some way. Some species may also be dependent on the presence of certain other species. If one of the goals of the project is to restore self-supporting native flora and fauna communities there is a greater chance of success through using typical associations to develop the plant list. This is a much better method as opposed to picking individual species without considering their interactions.
Also, keep in mind that the final community desired on site that must be created or restored may not be the one that is initially planted. For example, if the goal is to restore a native hardwood forest community on a site that has been cleared of trees, it would not be appropriate to plant herbaceous understory species that are shade-tolerant or intolerant to high light levels. Until the shady environment is created, those understory species will not survive and efforts and resources will have been wasted.
To help in selecting the most appropriate species, different resources are advantageous.
The best indicators of appropriate plant species may be native species that are already growing on the site, if there are still some left. An exception would be if the site has been altered enough for new native species adapted to different conditions to grow, rather than the originally present native species. In this case an evaluation of which native plant community is desired at the site: the original community or one adapted to the new site conditions. The challenge is to determine the factors keeping native species from growing throughout the entire site.
Another very helpful method of determining what native species to use is to identify a reference community. A reference community is the same type of ecological community as the project plans to have at the restoration site. It is always located in environmental conditions similar to the restoration site and provides an idea about what plant species to use for restoration. If there is enough historical data available, the reference community could be the community that was historically found at the site. However, if it is unclear what native species used to be present at the site, a reference community can also be an intact community of native species located near the restoration site in similar site conditions.
Local native plant experts and literature on local plant communities are two other resources that should be taken advantage of if the restoration team is not familiar with the native plants of the site's region. Historical records of a site, including include localized floras, local herbaria, aerial photographs, and first-hand accounts, can provide another good source of information. Many of these experts and information resources at the local conservation district office, the local office of the NRCS, the botany department of local universities, the county Cooperative Extension office of the state's land grant university, the state's Department of Natural Resources, the state's Natural Heritage Program (Appendix A) or an environmental consulting firm.
The plants in any restoration are part of an ecosystem which includes animals as well as plants. Especially in highly disturbed or developed areas, the plant community which is being replicated may no longer exist locally. For that reason, a thorough search of historic information is imperative to assure restoration to the correct plant community. Often there are small landscape scale differences in the composition of native plant communities of which only local native plant experts are aware. Having their assistance can help in avoiding the use of plants that may be native to the region, but are not appropriate to the particular planting site. Literature on local plant communities can also be helpful when determining appropriate plant species for the site's conditions. Plant books or articles may suggest native plant species that prefer certain types of environmental conditions.
When landscaping within an urban area, it does not matter as much where the native plant species come from as long as they are native plants to that region or area. For areas near public lands, National Forests or state lands with few introduced plants, first preference should be given to obtaining local native plant species from local plant materials. These concerns are based on genetics issues which are outlined in the next section. If local native plant materials are not available, consider using a non-persistent annual such as weed-free barley or cultivated oats to act as a soil stabilizer until native plants in the area can recolonize a site. Another option for small restoration sites, without noxious weeds or invasive plants nearby, would be to not seed at all and allow the local native plants to recolonize a site on their own.
Understanding the Importance of Genetics
There has been a growing awareness recently of the importance of plant genetics in restoration projects. Genetic variation within plant species can influence their long-term chances of survival and growth. An ecotype is a certain population of plants within a species that, due to different genetics, has a different form (height, leaf size, etc.), flowering time, resistance to diseases/pests or hardiness that is adapted to certain local environmental conditions. Plant ecotypes are not different species because they can still interbreed. Taking plant species that are of one ecotype and moving them to an area with different environmental conditions, such as different freezing stresses or different moisture levels, can result in poor growth or death.
These types of genetic concerns have long been recognized in the forestry industry. Tree seed zones have been developed for specific tree species based on an understanding of their genetic variation across the landscape. Seeds are only planted in the same tree seed zone they were collected from, in order to increase the plants' chances of survival and adaptability. However, it is only recently that some scientists have begun to examine the genetic variation of herbaceous or shrub species across the landscape. Consequently, there is very little information available about what might be the appropriate distance one could safely relocate native plant species when considering the gene pool.
In addition to concerns about the ability of the planted species in restoration projects to survive and adapt, some people are concerned that the introduction of new genetic material in an area can damage local populations of native species. The thought is that new genetic material could result in the weakening of local populations' ability to survive and adapt to environmental pressures. This particular concern is still being debated. However it is clear that without a better understanding of the genetic variation of the species, it is a safer option to avoid as much as possible introducing non-adapted genetic material that may have unanticipated detrimental effects. Also, because plant genotypes may contain very different chemical compounds, using the wrong genotype of a plant species can also cause death or injury to herbivorous species who depend on the plant (Longcore 2000).
Depending on the genetics, there may be very different strategies for the appropriate places to collect propagation material for specific species. A general rule to follow is, if information is not available on the plant species' genetic variation, try to use plant material of local genetic source whenever possible. There is no universal agreement as yet on the exact guidelines for "local" sources. However, selecting a plant material source where the following factors are the same or similar to the site can serve as a general rule of thumb.
- associated vegetation
- frost dates
- soil type
- temperature patterns
Because there are very few sources from which native plant material can be obtained, it may be difficult to get plants that are from as local a genetic source as desired. First, consider where the restoration project will be located, in an urban area or near public lands with very few introduced plant species. If the site is located near the latter, a broad guideline to follow is to ensure that the native plant materials originated from at least from the same ecoregion. There are a few different ecoregion classifications of the United States that have been developed. One popular classification is Bailey's ecoregions, a product of a cooperative effort among several federal agencies and The Nature Conservancy. These regions are areas that have been defined as having similar natural communities, geology, and climate (Appendix A). If local native plant materials are not available, it sometimes can be better to seed with non-persistent annuals such as weed-free barley or cultivated oats, rather than introducing non-local native plant seed from another area into the gene pool. For more information about how to determine if the native plant or seed supplier has the type of genetic stock preferred, see the section on Selecting a Suitable Supplier.
Active Reintroduction of Natives or Let Them Return Naturally?
Once the project's list of native plant species has been decided, the next step is to determine how they will be restored to the site. There are two major choices: allow natives to return naturally or reintroduce natives by direct seeding or planting grown plants. The choice can be made to use one approach or a combination of these options.
To decide which option is most appropriate for a particular project, consider the site conditions and the needs of the plants wanted. Seek information on successes and failures of similar projects. Good sources of information include journals like Restoration Management Notes or consulting with other local projects.
First it must be understood why native plants are no longer present on the site. This can best be determined by using the data collected during the site evaluation. Researching prior management practices and use history of the area is vital to determining which plants will come back on their own to the site. Is there anything the site evaluation found that would be a probable cause for the lack of native plants? For example, is there a disturbance such as the presence of grazers that has been preventing the return of native plants or have the soil conditions changed in some way so that they are not hospitable to native plants? If the restoration project changes the site conditions, such as removing the grazers or reconditioning the soil, sometimes that is enough to allow native plants to return naturally.
One of the advantages of allowing native plants to return naturally is the low cost; however, there are other important questions that should be answered before deciding to use this method. Perhaps the most important question is whether there is an adequate source of native plant reproductive material on or near enough the site to facilitate their return. There should either be native seeds in the soil seed bank or a nearby stand of intact native plant material that will be able to reproduce and expand into the site through seed production and germination or vegetative propagation. However, except in large tracts of wildlands, human disturbances have impoverished the soil seed bank.
The presence of noxious weed or invasive plant species on or near the site could mean that they reinvade along with the native species. Although an ideal and inexpensive method, relying upon native seeds in the soil seed bank is vanishing because the invasive species are more likely to appear. If the natural return of native plants is still the desired option and there are noxious weeds or invasive plants present, there should be a plan for active control of these weeds until the native plants have a chance to establish themselves enough to outcompete the weeds.
Finally, when considering the option to allow the natural return of native plants, the rate at which the natives may return and reestablish on the site should be compared with the project's desired timeline. The enhancement of natural revegetation includes creating seed catchments, mulching, and removing disturbances. Even using these enhancements, natural return is usually associated with a slow return rate which may increase the chances of failure if other factors are not controlled such as weedy plants or grazers. In this case, it may be more efficient to pursue a more rapid reintroduction of natives through seeding or planting rather than using time and resources for weeding and predator protection while waiting for the natives to reestablish. However, most projects will use a combined approach of active reintroduction and natural return of native plants because there is no single approach that will fulfill all the needs of a site.
Active Reintroduction: Seeds or Plants
If active reintroduction of natives seems to be necessary for the project, the next step is to determine whether seeding or planting would be most successful. There are advantages and disadvantages to both and, again, it may be most useful to try a combination. For each site and plant community, different strategies will be appropriate.
Seeds are an attractive option because they are less expensive than plants and are easier to distribute in a large restoration site. However, they also have a number of disadvantages. Seeds are more susceptible to predation from birds or rodents when they are first scattered. This is less of a problem if they are drill seeded. Seeds can take several years to establish especially if they are tree or shrub seeds. They are more likely than planted plants to be overcome by weedy species, especially at the early stages of germination and as young seedlings. Finally, if seeds have specific germination requirements that are not met they may not establish at all, or they may establish years later when requirements such as freeze-thaw cycles are met.
Propagated plants may be preferred because they establish themselves more rapidly, increasing the chances of success in a project. If project species are difficult to germinate, using plants that have already passed that stage ensures better establishment and survival. However, using plants will be more expensive than seeds. It is also more labor intensive to install plants rather than doing a direct seeding. Considerations should also include the time and labor that will be needed to maintain an outplanting project due to supplemental irrigation, protective cages, and other measures.
If planting or seeding on arid sites, keep in mind that provisions must be made for irrigation when natural water fails to occur. When using containerized plants on arid sites, irrigation will almost always be necessary until the plants are established. Establishment occurs when plant roots have grown sufficiently out of the container root ball into the native soil for the plant to be able to reach available soil water.
Ultimately, it depends on the needs of the specific plant species for the site. People who are working to restore plant communities dominated mainly by herbaceous species that don't have strict germination requirements, such as prairies, tend to use seeds. On the other hand, people working to reintroduce woody plants, which may be slow to establish or are difficult to germinate, tend to use plants instead of seeds. Sometimes a combination of techniques is most useful, such as seeding those plants that will germinate and establish easily from seed and then, after a few years, using seedlings for the other plants that have a more difficult time establishing from seed or planting overstory plants first and seeding understory plants later as conditions allow.
Sources of Seeds
There are a number of different options for obtaining the required native seeds. These options include
- using donor soil from a similar intact native plant community or development site (e.g., building construction or roadcut)
- weed-free wild hay from a native grassland or wetland
- collecting seeds
- buying local native seeds from a supplier or grower
The method chosen will depend on the type of plant species wanted, the availability of the seeds needed, and the resources available.
One option especially used in some wetland restoration projects is to find an intact native plant-dominated wetland from which some soil can be removed as donor soil (Galatowitsch and van der Valk 1994). This soil will usually have a number of native wetland plant seeds in it. To plant the seeds, the donor soil is spread in a thin layer across the restoration site. However, if this method is used, care should be taken not to damage the intact wetland unless it is about to be destroyed, disturbed or is in need of salvage.
If the donor site is slated for development (or a roadcut), the top 8 to 10 inches of soil can be removed and transported to the restoration site. If the donor site is to remain intact, then small amounts of soil can be removed from different zones and spread thinly in specific areas at the restoration site. If there is variation within the donor site in terms of vegetation types present and hydrology, probably the greatest success to be found would be to take the donor soil from the different areas separately and place them in the most similar places in the restoration site. In wetlands, it is important to remember that different plant species prefer different types of water inundation levels so an effort should be made to match up donor soil to the same water inundation levels in the site. Also, it is important to remember that not all the plants desired for reestablishment may have seeds in the seed bank, so using this method along with other methods will help to ensure greater plant diversity. For more information about this technique refer to the book Restoring Prairie Wetlands, An Ecological Approach (Galatowitsch and van der Valk 1994).
A second similar approach, used to acquire seed mainly for grassland restoration projects, is to collect weed-free wild hay from a native grassland or wetland. Hay is collected when the seeds of the native species have developed and matured, but have not yet fallen. When using this method it is important to find a site that does not also have the seed of undesirable invasive species that may cause problems at the restoration site. It is also important to closely monitor the flowering and maturation of seed of the native species at the collection site to ensure that the hay is harvested at the optimum time. Remember, however, that different species' seeds will mature at different times, so a series of smaller harvests at different times to capture more of the diversity of the site should be considered. Once collected, the hay can then be spread over the prepared restoration site. Also, remember it is an important collection ethic to leave enough native seed at the collection site so that the donor plant community's ability to reproduce and maintain itself is not damaged. If there are no noxious weeds or invasive plants nearby, native plant litter and seeds can also be raked in from the edges of a small restoration site.
Both using donor soil or weed-free wild hay as a source of seeds for the desired native plants can be attractive options because it is much easier to collect these types of materials rather than collecting the seeds of all the desired species individually. Another advantage of these methods is that the types and relative abundances of native species will usually be close to a typical local native plant community. The drawbacks of these two methods, however, are that it may be difficult to find a suitable collection site that has the desired species and very few undesirable species. In addition, as mentioned previously, sometimes these methods will miss some of the species that are desired, either because they do not produce as much seed or they produce it at a different time than the time that collections take place.
If the previous two methods are not appropriate for the project, but the use of seeds is still warranted, then collecting or buying them should be considered. Collection may be a preferable option for ensuring that the seed sources are local. With experience in native seed collection present, it is possible to have the project team gather the seed. Otherwise a professional native seed collector can be contracted to collect for the project.
If the decision is made to collect seed, keep in mind the amount of lead time required to do so. Seed can only be collected during the limited time that it is ripe - usually from less than a week to a month. If this window is missed, collection must wait until the next year or next growing season. It is very important to factor in this extra time when developing the schedule for different phases of a native plant project.
There are a number of important considerations to keep in mind when collecting seed. The guiding principles for collection should be ones that help ensure that the best seeds for the project are being collected while protecting the intact native populations from which they are being collected. The seed collection guidelines below are good for most types of native seed. However, there are a few types of seed that are more difficult to collect and store because they have unique handling requirements. If the types of seeds being collected are not familiar, make sure to check with an experienced seed collector before following these procedures.
|Do match the donor and restoration site conditions as much as possible: slope, aspect, hydrology, soil type, frost dates, temperature patterns, elevation, etc.||Plants adapted to similar environmental conditions are more likely to succeed at the planting site.|
|Do collect in an area geographically near to planting site.||Locally adapted plants are more likely to succeed at the planting site.|
|Don't collect in sensitive areas.||Protect sensitive populations.|
|Do make sure none of the seeds collected are from rare species - contact the state Natural Heritage Program for more information about rare species in the area (Appendix A) .||Protect rare species.|
|Don't collect from ornamental plantings or near other exotics.||Ornamental varieties of the same species may not have the environmental adaptations needed for establishment at the planting site.|
|Do avoid collecting in weed infested areas. If collection must be done in those areas, be careful not to collect weed seed.||Helps keep weed seeds out of the seed mix.|
|Do obtain permission from the landowner to collect seed on private land or the required permit(s) for public lands.||This is legally required, as well as common courtesy.|
|Do try to collect dry seeds on a dry day. Wet fruits such as berries can be collected on wet or dry days.||Collected seeds with high moisture content will lose their viability more quickly than drier seed.|
|Do make sure to collect when seeds are mature. The seed should not dent under a fingernail and should detach easily from the plant.||Increases germination success.|
|Do use paper bags or other "breathable" containers for dry seeds. Berries and fruits can be collected in plastic buckets.||Helps the seed dry out more quickly so it will retain its viability longer.|
|Do collect from large populations.||Helps increase genetic diversity, thus increasing the chances of successful establishment.|
|Don't concentrate on one small area of the plant population, instead collect from a wider area.||Helps increase genetic diversity, thus increasing the chances of successful establishment.|
|Do collect from different microhabitats within the site.||Helps increase genetic diversity, thus increasing the chances of successful establishment.|
|Do know the factors affecting seed viability of the species before collecting and processing them.||Short-lived seed such as willows and alders need to be planted immediately after collection, and kept cool until planting.|
|Do collect a few seeds from many plants rather than many seeds from a few plants.||Helps increase genetic diversity, thus increasing the chances of successful establishment. Also protects intact populations.|
|Do collect from a wide range of plants: short or tall, scrawny or robust.||Helps increase genetic diversity, thus increasing the chances of successful establishment.|
|Do leave at least 2/3 of the available seeds.||Protect natural populations.|
|Do communicate with other local collectors about where collections are taking place.||Important to protect the intact natural population to make sure one site is not getting collected from too many times.|
|Don't harm donor populations.||Protect natural populations.|
|Do immediately clean and dry seeds after collection or treat wet fruits appropriately.
Dry seeds: Spread out on paper or tarp in a dry place for a few days.
Wet fruits: 1.) Separate seeds out of fruit by pressing through a metal screen. Put the mashed fruit in a bucket of water and float off the pulp (viable seeds should sink to the bottom). Then dry the seed by spreading out on paper or tarps. OR 2.) Plan to store these fruits intact in a cool environment; then macerate fruit, float off seed and plant immediately upon cleaning without prior drying.
|Most cleaned and dried seeds have a higher viability rate. Seeds of many species of wet-fruited plants such as Baneberry (Actea rubra) and Toyon (Heteromeles arbutifolia) will often go into complex dormancies when cleaned and dried.|
|Do store cleaned, dried seeds in a paper envelope or a sealed plastic container with desiccant in a refrigerator until needed.||This will help maintain viability for a longer period of time.|
Finally, if it is not feasible for project staff to do the collecting, a contract can be made with a professional seed company to collect the seed or seed can be purchased from companies that already have that seed in stock. The advantages to contracting the seed collection is that collection can be tailored to make sure that collected seed is locally appropriate for the project. Ask the contractor if they follow the above guidelines when they collect seed. Keep in mind however, that sites will have to either be located by project staff or the contractor will need enough lead time to find the appropriate sites to collect the requested species and to wait until the seeds are mature and ready to collect. This may take at least one year. Contract collection may be the only way to get seed of particular species if it is not otherwise commercially available.
If local native plant seed is commercially available, this may be a more desirable option than contract collection because there is no reason to wait until the right season for collection. Many native seed suppliers keep careful records about the collection locations so it is still possible to match the seed collection locations to the project site.
One method of getting information about the original source of the seed collected is to request Yellow Tagged Source Identified Seed; however, this is not available yet in all states. The yellow tag indicates that the seeds were collected from a stand that was not bred for cultivation, either a natural stand or a production field where no breeding has taken place. The source identification lists the geographic genetic origin of the seed. The location listed is not consistent, but is usually either a county, a group of counties or a state.
It may also be useful to request an analysis label with each bag of seed. This label should state the species' scientific name, the purity of the seed (actual seed of the species present vs. other plant material, weed seeds, etc.), the amount of weed seeds present, the germination rate for the seed, and the amount of Pure Live Seed (PLS). PLS is the percentage of actual pure seed multiplied by the percentage of that seed that will actually germinate. However, keep in mind that, for many native species, currently there are no established testing techniques so germination test results may not always be completely accurate. The information provided on the analysis label can also help in comparing seed prices between different suppliers. One supplier may offer a lower price for their seed, however it may be due to the fact that it hasn't been cleaned as thoroughly, resulting in less actual seed per volume.
If there are concerns about the quality of the seed being purchased, testing can be done by an independent seed testing laboratory that has been approved by the Association of Official Seed Analysts (http://www.aosaseed.com/), keeping in mind that many of their methods have been developed for agricultural seeds. If the lab is not familiar with the germination requirements of the native species being tested, their results may not be accurate.
Be sure to check the identity of all seeds before growing them out, whether seeds have been collected by project staff, collected through a contract or commercially purchased. Some seeds being sold commercially are not accurately identified and their use may compromise the integrity of the restoration.
Sources of Plants
If plants are a better option or part of a combined approach for the project, to find the sources of native plants required the following options cover the various methods that can be used singly or in combination.
- contract with a native plant supplier to grow the plant material
- salvage plants from a site that is about to be destroyed
- collect and propagate the plant material using project staff
- buy already grown plants from a nursery
Contract with a Native Plant Supplier
Contract growing is favored by many experienced project managers that have the necessary amount of lead time to plan native plant projects. This option provides the flexibility to work with a supplier to determine which of the desired species can be propagated. Also it is the best way to ensure that all the species needed can be propagated and will be available for the project. Contracting a grower presents the opportunity to be more selective as to the original source of plant material used for the project.
Salvaging plants is a popular option in some parts of the country. Some established programs exist that salvage plants from areas slated for development, such as the King County Native Plant Salvage Program (Appendix A). These programs then make the plants available for restoration projects. Plants that survive the salvaging process best tend to have a shallow, compact root system, can tolerate a broad range of habitat conditions and are adapted to disturbance. This includes succulents and grass clumps. It is also important to take proper care of the roots of salvaged plants. Native soil should be kept intact with the rootball and transplanted with the salvage plant. The roots should be cut cleanly when first salvaged and then the rootball should be kept moist. If the plants cannot be planted immediately at the restoration site, there needs to be a good holding facility which can keep the plants moist and healthy until it is the right time to replant them. Remember that plants should never be dug up from an intact native plant community that is not about to be developed. Salvaging is a technique used only to save plants that otherwise would be destroyed.
Collect and Propagate the Plant Material Using Project Staff
This is an option that in most cases, should only be used if project staff are already experienced in plant propagation or will have the assistance of a plant propagator. However, there are a few cases when some plants are easy enough to propagate that it may be an attractive option.
One example of this is plants such as willow trees or red-osier dogwoods that are easily propagated from cuttings. This is a common technique used in stream or wetland restoration projects in some parts of the country. When the plants are dormant in the fall and winter, sections approximately four feet long and around half an inch in diameter can be harvested from straight branches of mature plants located near the site. The lateral branches and twigs are trimmed from the sides of the branch, and then it is planted at the restoration site (right side up) by pushing it into the soil until half is underground. It is important to keep the end of the cutting moist if the cuttings are not planted on the same day as they are cut. Also, make sure that, once planted, the soil is pressing against the cutting so root production is triggered. In the spring successful cuttings will begin sprouting branches and leaves. If working in a dry climate, always make sure the soil is moist or water the cuttings at the time of planting.
Buy Already Grown Plants from a Nursery
If the native species required for the project are a type that are commonly available in local native plant nurseries and there is enough available stock, this may be an attractive option for those who wish to acquire plants more rapidly. It is important to follow the suggestions in the sections on Selecting a Suitable Supplier and Evaluating Plant Material to ensure the nursery provides high quality plants. Nurseries should be contacted long before the plants are needed to allow them to make arrangements to have sufficient quantities available. In temperate regions, many nurseries will need to have an order in December to make sure plants are available for spring or summer planting.
Selecting Plant Product Types
Plant material is available in a variety of forms, each with advantages and disadvantages for native plant project planning. Nursery grown native plants can be grown in a wide assortment of containers, usually dependent on which species is grown, its growth habit (tree, woody shrub, annual, perennial, etc.) and its natural habitat. Ideally, the container chosen and the conditions in which the plant are grown simulate natural conditions as much as possible. For example, wetland plants can be grown in specialized beds that allow the soil medium to be saturated much of the time instead of completely draining. This mimics natural wetland conditions.
The following is a list of commonly available nursery stock types:
- BALLED-IN-BURLAP or "B&B" The plant is grown in the field, dug up with its roots and surrounding soil, and wrapped in a protective material such as burlap.
- BARE-ROOT The plant is sold without any soil around its roots.
- CONTAINERS The plant is sold in a container of soil with drainage holes. Sizes and shapes of containers vary, but they are usually plastic. Examples of common sizes are: 4" pots, 6" pots, and 1, 2 or 5 gallon containers.
- CUTTINGS or WHIPS A piece of branch, root or leaf that is separated from a host plant and is used to create a new plant. These may be placed in a rooting medium or stuck directly into the ground for planting.
- LINERS A small grafted plant, rooted cutting or seedling that is ready for transplanting. They are often used for herbaceous plants and grasses.
- PLUGS or TUBELINGS These are similar to liners, but they are individual cylindrical or square planting containers that are longer than they are wide. The longer shape provides room for a plant to build root mass for transplanting.
COMPARISON OF PLANT MATERIAL FOR RESTORATION PLANNING TYPE ADVANTAGES DISADVANTAGES BALLED-IN-BURLAP
- Well-developed root systems increase chances of survival on site
- Provide shade and earlier establishment of upper canopy on site
- Large and heavy to transport
- Less expensive
- Easier to transport to site, lightweight to carry around for planting
- Roots have not been restricted by containers
- Require care not to let root systems dry out before planting
- Difficult to establish in dry sties or sites with warm, sunny spring seasons
- Well-established root systems with intact soil
- Provide "instant" plants on site
- Available in a variety of sizes, many are available year-round
- Native soil not used in nursery, transplant shock may occur when roots try to move in to native soil
- Can be expensive
- Can be difficult to transport to and around site if large amount is used
- Can be difficult to provide irrigation until established, may actually require more maintenance than plugs
- Well-established root systems with intact soil
- Easy to transplant, plant material pops out of containers easily
- Same as above
- Smaller plants may take longer to establish, require more initial maintenance
- Inexpensive to produce
- Cuttings may easily be taken on site or from nearby site
- Easy and light to transport
- Known to work well in rocky areas or areas difficult to access
- No established root systems
- Timing of taking cuttings and planting them is important, varies among species
- Inexpensive compared to plant material
- Variety of seed available commercially
- Easier handling than plant material
- Seeds of different species have different germination and storage requirements
- Potential losses from birds, small mammals, etc. eating seeds on site
- Slower establishment on site
- Can use plant material that would otherwise be destroyed
- Plant material could be local to site
- Relatively inexpensive
- Small or young salvage plants often adapt more readily to transplant than do mature specimens
- Different native plants respond differently to being dug up, some loss could be expected
- Requires fairly intensive measures to protect plants and ensure they have adequate irrigation
* "SALVAGE" refers to the process of removing native plants from a site before ground disturbance at that site occurs. See the previous section, "Sources of Plants" to read more about plant salvaging techniques and requirements.
Timing, as mentioned in previous sections, is an important element when considering which types of plant material to use. Local seed could be collected to match site conditions, but different species produce seed at different times of the year, and have different storage requirements. If any of the work is to be contracted, advance planning is crucial so that a suitable, qualified contractor can be found. As more native plant nurseries become established and more nurseries begin to grow out local native plants, a wider variety of plant material types and species become available. Some nurseries will grow out specific plants under contract. If plant material is to be propagated from site-specific stock or seed, a few years may be necessary to grow the plant material.
Another consideration is the optimum size of the plants that are being used. Big plants seem preferable to some who would like to see some large plants established quickly. In some sites where maintenance after planting was not possible, planting larger plants helped to increase total survival. However, others have found that more mature plants sometimes have difficulty adjusting to their new environment and may not survive. Also big plants can be very expensive. For many, smaller plants are a more attractive option because they are inexpensive, easier to handle, and they often can more easily adapt to the new site conditions. However, it does take longer to develop large established plants on a site and they may require more initial maintenance.
Micropropagation, or tissue culture, is a vegetative method for multiplying plants in which a whole plant is produced from a very small piece of plant tissue. Although not always economical or as desirable for many native plant species, it can be the desired form of native plant production in specific instances, such as:
- seeds are not available (in the case of some rare native plant species, very little seed is produced)
- seeds are difficult to handle or propagate
- cuttings are vulnerable to disease and/or require too much care
- cuttings have a low survival rate
- existing shortage of stock plants from which to take cuttings
During the micropropagation process, a piece of a plant (e.g., stem, root, leaf, bud, single cell) is placed in a test tube or another form of culture that has been supplied with the nutrients and growth hormones the plant needs. In a controlled environment, the new plant material, known as a plantlet, develops tiny roots, shoots, and leaves similar to a seedling. When the plantlet is large enough, it is transferred to soil outside of the laboratory where it produces leaves of normal size and assumes the likeness of the parent plants.
While micropropagation enables the production of many plants in a short period of time, there is concern about the lack of genetic variability in the cultured plants. Since new plants are being created from the tissue of old plants without the mingling of genes that is associated with non-vegetative or sexual reproduction, no new genetic variation is being added to the population. In other words, clones are being produced.
For many native plant species, vegetative reproduction occurs naturally and frequently. So, the concern about limited genetic variation does not apply to all species, especially those that are widespread and abundant. However, it is important to approach micropropagation for restoration purposes in a conservative manner when genetics are considered. One way to increase the genetic variation in the new plant population is to culture tissue from numerous stock plants and grow only a few plantlets per stock plant. Similar to seed collecting guidelines, remember to use a wide range of stock plants (short, tall, scrawny, and robust) in order to increase genetic diversity.
Selecting a Suitable Supplier
It is an ideal situation if the expertise, equipment, and staff are available to produce propagated native plant material or native seed on site for the restoration project. However, this is usually not feasible. Often a suitable supplier must be chosen to perform the work. Native plant material is available from retail or wholesale nurseries or specialized growers. Native seed is available from commercial seed suppliers. Some nurseries, growers, and seed collectors may specialize in native plants and some may only include them as part of their business. Choosing a supplier who specializes in native plants and seeds is desirable, but is not always an option. Checking with a state's native plant society can sometimes yield a list of suppliers who specialize in native plants.
Again, timing is extremely important in this phase of restoration planning. It is virtually impossible for suppliers to keep a giant inventory of native plants and seeds on hand at all times. Suppliers try to anticipate needs for variety and quantity of native plants and seeds, but it is difficult. Also, it can take several years to grow plant material or collect seed for a specific project. This is very important to remember when searching for a supplier to help with acquiring the plants or seeds needed.
Plant Material Suppliers
Select nurseries or plant growers that have experience working in the site's ecoregion and carry plant materials or can collect plant materials from the project area (within the same ecoregion). The supplier should have staff knowledgeable about local native flora. If specific plants are to be grown for the restoration project, interview the grower about their knowledge of propagating all planned species. Ask them to send catalogs and/or price lists if available.
Find out where and how the plants being sold have been grown. Plants may have been grown in a very different part of the country and consequently, would not be well-suited for the restoration site. Make sure plant material has never been dug from the wild and removed from its natural habitat. Unfortunately, this practice does occur and has negative far-reaching effects on natural systems and native plant populations. Nursery owners and growers should assure the customer that all plants have been "nursery propagated." This means that staff have collected only seeds or cuttings from the wild, and have not removed whole plants from the wild. Also request that the supplier supply information about the original location of the parent plant material to aid in determining how locally adapted the plants might be. Good native plant nurseries will have this type of information on record. If plants have been salvaged, ask the staff person where and how they were salvaged. Ethical salvage occurs when plants are removed before some type of construction or destruction takes place and always with the landowners' permission.
Plan to visit the nurseries. Nursery grounds should be clean and orderly. Survey plant material for general vigor and health. Note the presence or absence of weeds on the grounds or in container plants. Some weeds are acceptable, since it is extremely difficult to completely control weeds in nurseries. Many nursery operators are trying to reduce their pesticide use and may therefore be weeding everything by hand, which is time-consuming. Note how well equipment on site is maintained and cared for such as tractors, greenhouse systems, and irrigation systems.
Nurseries and growers may advertise membership in professional trade organizations such as the American Association of Nurserymen, International Society of Arboriculture or their state Nursery and Landscape Association. Although these trade memberships are not required for operation, they show that the owners care about keeping abreast of current issues, regulations, technology, product improvement, and other pertinent information in the nursery trade.
Many of the considerations for choosing plant material suppliers also apply to choosing seed suppliers. Again, try to choose a seed supplier that operates in the same geographic ecoregion as the restoration site, as that supplier is most likely to have native seed suitable for that area. There are companies which specialize in native seed collection, processing, and growing. These companies can have a wealth of knowledge about native plants and seeds. Ask them to send catalogs and/or price lists if available.
It is helpful to become familiar with several terms when ordering seed to assist in making informed decisions:
Certified Seed (blue tag)
This certification only applies to seed produced through cultivation, not seed collected in the wild. The seed certification system promotes the production and purchase of seed of known genetic identity and is used widely in the traditional agricultural field. Only cultivated, named varieties can be certified. Each state has a certification agency that inspects field conditions and regulates how the seed is produced, harvested, and cleaned. The seed is also subject to a variety of laboratory tests. If the seed passes these tests, it is certified by a state agent with a blue tag. This certification process guarantees the seed has the same genetic potential to perform in the field as the original seed did when it was released for production. This type of seed will only be available from the larger seed companies. Sometimes it is necessary for native seed suppliers to cultivate native seeds if the amount of seed needed is greater than what could be harvested in the wild without impacting native populations. However, it is important to consider how growing all the seed together in a cultivated area may have altered the genetics of the seeds. They may no longer be as adapted to the environmental conditions they may experience on the planting site. Native plants grown from certified seeds may also hybridize with local native plants and pollute gene pools. In light of this, not all projects accept cultivars for planting.
Source Identified Seed (yellow tag)
The Association of Official Seed Certifying Agencies (AOSCA) has an approved seed certification class for native seed collection called the "Source Identified Class." Seed that was harvested following approved guidelines for this seed class will receive a yellow certified seed tag. The tag confirms to the purchaser that the location of seed harvest was verified by the certifying agency. This yellow certification is not available yet in all states.
Pure Live Seed (PLS)
Pure live seed is a measure describing the percentage of a quantity of seed that will germinate. It is a way to standardize quality so the purchaser can compare the quality and value of different lots of seed. One lot may be cheaper, but may not have as high a PLS as another lot, and so therefore may not be a better deal financially because it would have fewer seeds that would actually germinate. See the section on "Seeding Restoration Sites" for more information on calculating the PLS.
Seed Testing and Labeling
Seed companies should include a clear label on each bag of seed that shows the results of purity and germination tests, and the scientific name of the species. The Association of Official Seed Analysts oversees these tests. Purity of the seed is the percentage of the labeled species by weight. The percentages of other crop, weed, inert material, and the percentage of dormant or hard seed should also be included. The label should also show the percentage of the seed count that will germinate. Keep in mind however that many seed labs are still not that familiar with native seed germination requirements and so may not accurately estimate the germination percentage. New tests need to be developed.
Some companies offer custom seed mixing services that involve creating a seed mix from species chosen by the customer. However, the drawback of purchasing pre-mixed seeds is that it becomes difficult to confirm the identity, purity and quality of the seed being purchased.
Site Adapted Custom Seed Collection
Some seed companies also may offer collection services where they will harvest seed from sites the customer specifies. This is a preferred way to go for many that want to ensure that their seed is from local sources.
Seed companies offer a variety of shipping alternatives that can be arranged upon ordering. Again, it is a good idea to interview the staff about the seed company's harvesting methods to ensure ethical collection has taken place. See the seed collection guidelines in the "Sources of Seeds" section to learn more about ethical seed collection practices.
Evaluating Plant Material
All plant material is not created equal. Quality plant material is an important ingredient in a successful restoration implementation. It is important to evaluate plant material before deciding to purchase it from a commercial supplier or accepting material that has been grown specifically under contract for a project. Plants come in all shapes, sizes, and life forms, but understanding some basic characteristics of nursery grown plants will help project managers make informed decisions about purchases.
There are written specific guidelines for nursery stock entitled "The American Standards for Nursery Stock" (American National Standards Institute 1986). However, these standards pertain specifically to woody landscaping materials only and are not necessarily appropriate for native plant material. The nursery stock standards include acceptable specifics for height to caliper ratio, taper, crown configuration, and branching pattern. These specifics are included because, in the landscape industry, uniformity of plants is a desirable trait. However, in the native plant world, diversity is a more desirable trait because it is an indicator of genetic diversity.
Having good mental images of the growth habit and form native plant species have in their natural habitats will help in the evaluation process. There are several general characteristics to consider when examining plant material. The negative characteristics mentioned are not necessarily fatal to the plants, some can be corrected, but if all or most of the plant material examined has potential problems, it may be better to look elsewhere for plant material.
This is a subjective assessment of how healthy plants appear, and can differ depending on time of year or the physiological state the species is in at the time. Generally, plants with green, turgid leaves and robust stems are vigorous. The plant should be able to stand upright on its own without stakes or supports. Spindly growth, dry or discolored leaves or tissue or insect damage are all examples of signs of weak plants. Conversely, bright green, soft plants of extremely vigorous growth which have been grown with constantly high levels of nitrogen fertilization may not be able to survive the rigors of the native site without a hardening-off treatment.
Plants should generally be free of injuries, wounds or insect damage. Mechanical damage includes such injuries as broken off shoot tips, cuts or digs in the stems, and severe pruning.
Not all organisms or indications of their presence are necessarily harmful, but generally plants should be free of insects, signs of disease, galls, cankers, fungus, or weeds growing in the potting soil.
At least one plant, ideally all, in a lot should be clearly tagged with the correct botanical scientific name of that plant.
Native plant material need not be exactly the same height and width. Landscape nurseries usually strive for this likeness among plants because customers are assured that one plant is as good as another. However, variability is a desirable characteristic in native plants in their genetic, and thus physical, makeup.
A healthy root system is extremely important for plants since roots provide the mechanism by which plants absorb nutrients and water from the soil to survive and grow. The top of a plant may appear healthy, but the plant could have root problems in the container. This could threaten its survival later. It is easy to inspect the root systems of bare-root plants. To inspect the root systems of container plants, randomly select several plants and turn them upside down so they pop out of their containers. The root system should have healthy main roots and plenty of smaller fibrous roots. The plant and its rootball should come out of the container as a unit and the rootball should hold most or all of the soil together. If the plant can be pulled out without any intact soil, it is not well rooted in its substrate.
ROOT CHARACTERISTICS TO EXAMINE (Hummel)
Circling or kinked roots
- plant may have remained in its container too long
- if these types of roots are at the periphery of the root zone they could be root pruned before planting, if they occur close to the main stem and/or in the central root zone, they are difficult to correct and could eventually girdle the plant
Root tip color
- white-root tips are healthy and actively growing
- brown/discolored-roots may have been injured (frozen, salt, over watering, poor drainage, disease, etc.)
Circling roots at bottom of container
- plant may have been under watered
- top of the plant may not be balanced with the root system
Roots mostly at top portion of container
- plant may have been over watered
- container may not have been well-drained so there was little oxygen available at the bottom of the container
Roots mostly on one side of container
- temperatures may have been too hot for roots on the other side of the container (e.g. may have always been exposed to the southwest and strong sunlight)
Roots all swept to one side in a "J" shape
- roots may not have been spread out and centered when planted into the container
Roots coming out of drainage holes in the bottom of containers
- oxygen, water, and nutrient resources may be limited inside the container (taken up by other roots)
- potting medium is too wet inside the container so little oxygen is available
Plants should be handled carefully and protected during transport from the nursery. If they are to be transported in a truck, for example, it would be best if the truck had a canopy, sideboards or an enclosure of some kind (e.g. a tarp) to protect the plants from the elements. Plants transported in an open truck at high speeds can be severely damaged by the high wind conditions. Temporary storage before planting should be sheltered from wind, extremes in hot and cold temperatures, and potential injury. Bare-root plants should be kept in a dark, cool, moist location to prevent the roots from drying out. The roots could be wrapped loosely in moist burlap, where air could still circulate around the roots. Plants in dark containers should also be kept in a cool location, as direct sun can greatly increase the temperature in the container and damage fragile roots. Plants should also be watered regularly. A nursery employee could explain what watering schedule the plants have been on recently.
It is beneficial to allow plants to "harden off" before they are planted. This is a horticultural term that refers to the acclimation of a plant to its new environment. Conditions at the restoration site could be extremely different than the nursery setting in terms of temperature, exposure, and elevation. Plants should still be watered, but allowing more time between waterings will help harden the plants off. Plants could be allowed to remain on site for a few weeks for this process to be effective depending upon the differences in conditions between the nursery and restoration site. It is important to water plants properly to avoid crown rot.
Writing Specifications for Obtaining Plants from a Commercial Grower
The quality of the plant material used in a restoration project is as important to the ultimate success of the project as the proper planning, site preparation, and site maintenance. To ensure high-quality plant material is obtained from a nursery or contract grower, very detailed information about the species and characteristics of plants needed must be specified in a written contract. As applied to native species, the concept of plant specifications is new because, until very recently, specifications were only used for ornamental plants in traditional landscaping applications. Consequently, there are no hard and fast rules regarding specifying native plant material from a commercial grower. However, some basic dos and don'ts that will help to ensure quality plant material are outlined below. Information on writing specifications for seed collection is provided in the next section, Writing Specification for Seed Collection or Field Production.
- Order ahead. One year ahead for seed and 3 years ahead for seedlings or larger plants.
- Specify that only locally-adapted plant material be collected and that the exact collection locations be documented. The collection locations should be documented regardless of whether they have been selected by project staff or the nursery.
- Provide exact information on the number of each species and size of each plant that is required. Size should be specified by container size (in gallons) or pounds, a range of plant heights, and a range of stem diameters when appropriate. Take care to ensure the range of heights and diameters are appropriate for the natural growth habit of the particular species requested. Make sure there is enough flexibility in the ranges to ensure plenty of genetic diversity.
- For containerized seedlings or balled-in-burlap plants, specify that the root ball stay together when removed from its container or burlap and that the root ball fills the container.
- Specify that containers are weed free.
- Know the species. Knowing the species that is being worked with will allow for better and more cost-effective specifications. For example, groundcover species have shallow roots so they do not need large pots. Also, tap-rooted species and species sensitive to root disturbance should be grown in deeper pots and should not be specified as ball and burlap or bare root.
- Specify planting media, fertilizer regime, and desired mycorrhizal inoculation. Residual chemical fertilizers may create weed problems or water quality problems at the site. Certain soil mixtures may be excessively drained or hard to keep moist at the restoration site. Inoculation with mycorrhizae at the earliest possible stage of nursery production may promote a higher transplant success rate.
- Inspect a small sample before accepting all of the plant material. To do so, pull out a sample and check the roots. If the plant is root bound or has severely circular roots, then do not accept it. Also look underneath the leaves with a hand lens for insects and disease. Also, inspect species to verify proper identification.
- Use ornamental or cultivated varieties of native species. The ornamental varieties have been bred for aesthetic values, not to be adapted to certain environmental conditions. It is best to avoid using them if at all possible.
- Accept "equivalent" species. It is common practice in landscaping to substitute an "equivalent" species when the requested species is not available. This may be acceptable in an ornamental landscape but it is not acceptable in a native plant project. Specifically indicate in the contract that substitutions are not allowed unless specifically agreed upon.
- Specify that there be very little insect damage or disease. Some damage from insects and a small amount of disease (such as fungal spots) should be accepted and will not result in decreased survival of the plants. Otherwise the choice of plant material will be more limited and probably more expensive.
Writing Specifications for Seed Collection or Field Production
It is important to write clear specifications for a seed collection contract in order to get good results and maintain clear expectations and communication between the participating parties.
- Decide what species will be collected, the amounts of each species, and the form they should be in. The species should be specified by its scientific botanical name including variety, if applicable. The amounts should be specified in pounds, bushels or other such specific units. The form should be specified using botanical terms for fruiting bodies of plants for example, clean seed, pods, capsules, utricles, achenes, seed head or fleshy fruits. Be familiar enough with the species so that the specifications make sense. Consulting with a local native plant expert or a supplier can help if more information is needed on a species.
- Will the collection areas be chosen by the project staff or will the contractor be responsible for identifying them? If the contractor is responsible for identifying seed collection areas, the contact cost may be more expensive because extra time will be involved to accomplish this. However, if areas are identified by project staff, be sure that these are areas which will provide enough seed for the project without causing damage to the donor population. General areas for collection should still be specified for seed collection such as within certain watershed boundaries, elevation bands, slope, and aspect.
- If possible, include a questionnaire in the contract asking the bidder to outline their related experience. Ask questions regarding seed collection and processing experience, plant identification skills, and tools and equipment that will be used to accomplish the task.
- Will seed cleaning be done by the supplier, project staff or another facility/contractor? Clean seed will be more expensive, but a finished product would be received at the end of the contract.
- How will seed be stored prior to delivery? Certain species require cool moist storage or viability is lost.
- Write specifications for what is deemed viable, vigorous seed. Acceptable seed should be ripe without any evidence of insects, diseases, environmental or other types of damage.
- How will the seed be accepted upon delivery? What type of containers or bags should it be delivered in? Generally, seed should be accepted completely dried only, unless the plan is to dry it using project facilities. How will the seed be weighed and inspected? Will there be an established level of acceptable chaff (extraneous leaves, twigs, dried flower parts, etc.) that may require the seed to be cleaned upon delivery? It should be transported and stored in cool, dry conditions and packaged to protect the seed from the elements, rodents, insects, and disease. Or transported accordingly due to wet fruits and their specific needs.
- How is the contractor required to record information about each seed lot? At a minimum, two tags should be filled out for each seed lot in case one is lost or damaged. One could be placed inside each bag of seed and one stapled on the outside. The species name, place of collection, estimated number of parent plants collected from, elevation, date of collection, and name of collector should be recorded for each lot. In addition, maps of collection sites and daily logs of the contract progress are extremely useful.
- Do not allow contractor to collect in wilderness or protected natural areas of any kind. If collecting on any private land, make sure the owner's permission is granted. Specify arrangements for any specific permits needed.
- Include a section on genetic diversity. Seed lots should be kept separate according to species and collections site. Collections should be made from a large number of unrelated plants. Collecting should be dispersed throughout the collection site and not concentrated in one area. Collectors should not remove all of the seed from any given site, and ideally should leave at least two-thirds of the seed for natural reproduction.
- Provisions should be written to cancel or reduce the amounts requested in case it is a bad seed crop year. A range can be specified as acceptable for each species beginning with zero (in case that species does not produce an acceptable seed crop) up to a maximum amount acceptable. This protects both parties if good seed is not available. Often, substitutions can be made if another desired species is producing ample seed. These provisions should be agreeable to both parties and specified in the contract.
- Decide payment methods and procedures. Normally, contractors are paid by the pound or bushel for their efforts, and not hourly. However, this may not be feasible for collection of site-specific native seed. If species are not growing in monocultures or collections need to be done at many diverse populations, collection may be very time-consuming.
- Arrange a pre-work meeting before the contract begins so a schedule can be created along with a method of communication. Decide how to monitor progress of the contract through reports, regularly scheduled meetings or other communication methods.
- If possible, monitor seed development of each species to assess seed production and vigor, in case any changes need to be made in the contract.
- Plan ahead for provisions to process, store or plant the seed once delivered.
Next: Preparing The Site