In an arboreal TED-Ed lesson written by Valentin Hammoudi and animated by Doug Alberts, narrator Addison Anderson explains the “hydraulic limitation hypothesis,”, which posits that a tree will stop growing once it reaches a certain height. Included in this model are transpiration, capillary action, and root pressure, all of which struggle to function when a tree grows too tall .
Together these forces launch sap to dizzying heights, distributing nutrients, and growing new leaves to photosynthesize – far above the tree’s roots. But despite these sophisticated systems, every centimeter is a fight against gravity. As trees grow taller and taller, the supply of these vital fluids begins to dwindle. At a certain height, trees can no longer afford the lost water that evaporates during photosynthesis. And without the photosynthesis needed to support additional growth, the tree instead turns its resources towards existing branches.