Have you ever wondered why plants have such varied architecture? Among the selection pressures shaping the planet’s flora, heavy burdens of snow have been major. This past week’s spring surprise, though very brief, showed how differently the plants in our forest handle this kind of stress.
Six inches of dense heavy snow falling within a few hours is not a common occurrence in the Ohio River Valley. Already wet with rain, even the smallest of branches accumulated a uniquely heavy burden. How well the plants of this forest handled the weight has a lot to do with their sizes and shapes.
Snow cover was particularly heavy on the larger, densely branchy Spicebush shrubs. A few of the male Spicebush were already blooming, the others thick with buds ready to burst. Many large branches were bent nearly to the ground, but surprisingly almost none snapped, showing a high degree of flexibility. This is a good adaptation for an understory shrub that may have trees and limbs falling on it from time to time.
Some smaller trees, particularly spindly light-starved Hackberries, were also weighted nearly to the ground. I’ll be curious to see if this brief bending exercise has any lasting effects.
The flora of northern and mountain forests consists largely of snow-adapted conifers, whose drooping aspect and slippery needles allow them to cope with a heavy load. Our tall branchy deciduous trees, many leaning already, can’t shed snow so easily. The trees in the pic above were bent surprisingly low, and the stress was quick to target areas of weakness and decay. As I was taking these pictures, the sharp crack of limbs snapping made me more jumpy and vigilant than usual!
Some forest giants, like the last declining American Elms, lost huge chunks of themselves.
For anyone who’s thinking climate change means earlier, warmer springs – think again. More likely it means greater unpredictability, with a wider range of possible weather conditions and more extreme weather events. These stresses will shape the future of life rather quickly, as selection pressures “weed out” the less adaptable. Yet another reason to preserve and restore as much diversity as possible.