Why Buttressed Trunks on Wetland Trees?

OK, no comments on the blog, but here is one answer that nature offered to me while I was conducting a study many years ago (in 1995, in fact). I was doing a followup survey of a population of box turtles that had been marked 50 years earlier. The questions were: how many turtles were still alive five decades later, and what was the current status of the population? The site was a floodplain forest of Maryland's Patuxent River in the current Patuxent National Wildlife Refuge.

While searching for turtles, I snapped the accompanying photo of beaver damage to a beech (I think) tree. Note where the beavers have (and have not) chewed, and envision the impossibility that they could proceed around the entire circumference, thereby girdling, and ultimately killing the tree. The grooves or creases between the buttresses seem to be inaccessible to beaver teeth, and the animals had to make do with the convex surfaces on the buttresses.

But there are no (or at least very few) beavers in Florida, you might say. I would counter that fossil beavers were common here, perhaps 20,000 years ago. But really, beavers are unnecessary, and the trees are probably older than beavers anyway. Picture the damage that might occur to the lower bark of trees in swamps during raging floods that carried tree trunks and other heavy debris downstream. Like the Maryland beavers, the flood-borne materials could surely abrade bark from tree trunks, threatening their survival. However, with buttressed trees, the exposed buttresses of flooded trees might be abraded, but the bark in the concave surfaces between buttresses would be relatively safe. So protected, the trees could live to endure many more floods.


P.S. Re: the box turtle study. A few turtles first marked in 1945 remained in 1995. And the population, although apparently devastated by severe flooding caused by Hurricane Agnes in 1973, appeared to be on the road to recovery. Regrettably, although we published our results, no subsequent publications have documented the later status of the population.