Two main opposing forces affect a
tree's height; one pushes it upward while the other holds it down. By analyzing the interplay between these forces in coast redwoods (
Sequoia sempervirens), a team of biologists led by George Koch of
Northern Arizona University calculated the theoretical maximum tree height or the point at which opposing forces balance out and a tree stops growing. This point lies somewhere between . On the one hand, the researchers found, trees in forests "desire" to grow as tall as possible to overtake neighboring trees and reach stronger sunlight. On the other hand, gravity makes it more and more difficult to haul water upwards from the roots to the
canopy as the tree grows, and
leaves thus become smaller near the top. They discovered that despite the moistness of the ground far below, the leaves at the treetops struggle to get enough water, so they are effectively living in a constant drought. The difficulty of getting
water so far up into the sky is what ultimately constrains growth. Other researchers have developed models of maximum height for Coast Douglas-fir (
Pseudotsuga menziesii var. menziesii) trees that yield similar estimates of , a range that includes the height of the tallest reliably-measured historical (dead) specimen, a 126-meter tree. == Other claims of superlative height ==