How Tall Do Trees Grow??
Source: The Torii, the newsletter from Schedel Arboretum and Gardens, Vol.8.7, Spring 2006. Schedel Arboretum and Gardens, PO Box 81, Elmore OH 43416, (419) 862-3182
Concolor Fir in the Governor's Grove
We have a tendency to think of trees just growing taller and taller each year. But when we stop and think about it, we realize there must be a maximum height. So, there must be some factor(s) that come into play that controls just how tall a tree can grow. There are of course many things that limit growth including climate, soil conditions, genetics, etc., however, if we get a little theoretical and look for that “ultimate” factor, the answer comes down to fairly basic physics. As a practical matter, all plant parts require water, including the leaves at the top of the tree. At one time it was thought that the trees pushed water to their tops utilizing air pressure as it does when we “suck” water through a straw (We don’t really pull water up a straw, we withdraw air from the straw and atmospheric pressure pushes water in replacing the air). Numerous physiological studies in the last century clearly demonstrated that water is pulled through roots and stems to the top of a tree. Some aspects of the mechanism are somewhat of a mystery, but botanists have a basic understanding of the process.
So, how tall can a tree grow? To answer the question, we first ask how tall do trees actually grow, and this questions turns our attention to the giant redwoods in California, the tallest of which towers to a height of 370’ (Three times the height of trees we are accustomed to seeing in our forests). So, how much higher might a redwood tree be able to lift water without violating any laws of physics? A scientist at Northern Arizona University investigated this question and concluded that the absolute maximum height to which a redwood could lift water would be 427 feet.
Don’t ever expect the trees growing in your backyard to reach 427’, even if they are redwoods – there are always a variety of factors in nature that prevent an organism from reaching its theoretical limits.
The moral to this story is that there are always absolute limits in natural processes and it is important that we understand the mechanisms that impose the limits. In the future it is likely that botanists will look at redwoods and compare their anatomy and physiology with trees that attain lesser heights in order to get ideas for how to breed or genetically engineer new varieties.