Trees - The Challenge of Height
What I've plotted here is plant height against stem diameter. Each one of these data points is the largest individual representative of its species. Or, I should say, it's the largest individual representing its species. There are literally thousands of data points here, some of them even obscure one another. But, take a look at this relationship between plant height and stem diameter and you see an area that's occupied by numerous species. Then you see nothing over here. Understanding why this area is totally unoccupied, and why this area is occupied, is a challenge to a biologist like myself.
The question is not how did this space become occupied but, what's keeping things from living to heights with stem diameters here from occupying this space here. I have an explanation. I think a reasonable one. It has to do with the fact that plant stems are composed of many different kinds of tissues that perform a variety of functions. But, each of those tissues helps mechanically support stems against the pull of gravity of course. You also understand that these different types of tissues have different physical properties which means that some tissues do the job of stiffening and strengthening stems a little bit better or a little bit worse than some of the others. We can actually quantify that.
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