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.
When, at a certain height, leaves (or, in the case of redwoods, needles) are not cost-effective — the energy they rein in through photosynthesis doesn’t pay for the energy to bring them water — then the tree stops growing.
“As trees grow taller, increasing leaf water stress due to gravity and path length may ultimately limit leaf expansion and photosynthesis for further height growth,” the biologists wrote in a 2004 article in the journal Nature. This limit lies at or just above 400 feet.
Many factors account for the extreme height of redwoods, including the temperate Northern California climate, nutrient-rich , abundant rainfall, fog and even the tightly-packed redwood forests, which force trees to shoot upward in pursuit of sunlight. These conditions combine to make redwoods not simply the tallest trees in the world, but by Koch’s and his colleagues’ calculations, almost as tall as they could possibly be.