As it starts to get colder, animals have several options. “Leave for warmer places” is the primary strategy of migratory birds. Many animals take the “Find somewhere warm and stay there” strategy that is my personal approach to winter. Many animals find warm dens for the winter and hibernate, avoiding the cold and snow altogether. Finally, there is the “Bundle up real warm and live with it” strategy of of some of the fluffier varieties of wildlife. Of course, some mix and match of strategies is common; Venturing out for food and returning to a warm den is common enough.
But plants have one major handicap to their potential strategies. Unlike animals, which can move, plants are rather stuck. This means that a tree has no choice but to go with the “Live with it” strategy for coping with cold. Consequently, the trees we have in the area tend to be rather well equipped for that strategy.
We’re dominated by evergreens, or conifers. Conifers do not generally shed their leaves in the fall. The reason for this is that they don’t generally need to. The needles of a conifer are shaped very differently then the leaves of a broad-leafed tree (such as a maple), despite having pretty much the exact same purpose. Not losing all the leaves (they will lose some to wear and tear) is a huge advantage; it means that conifers can keep doing photosynthesis as long as there’s enough warmth and light to do so.
Why the needle shape? Snow load. Everything about the shape of a conifer helps with snow load. A tree is a lot like a roof, in that it can be damaged by the weight of accumulating snow. Conifer needles are shaped to avoid accumulating snow, and each needle will hold far less snow than the leaf of a deciduous tree. The tree itself is shaped to shed snow, with branches that tend to be fairly flexible. While branches may break from a particularly wet (and thus heavy) accumulation of snow, for the most part they bend and shed snow.
Freezing is, for most living things, a pretty serious problem. Water expands as it freezes, and at the cellular level this is quite destructive. Conifers avoid serious damage from this by allowing water outside of the cells to freeze, and by having cell walls that are harder, hard enough to generally withstand the pressure of expanding ice.
The final challenge of winter is not drying out. For conifers, that especially thick waxy coating on the needles is a way of preventing that.
Lessons to be learned from conifers?
- Too much snow piled atop one is a bad thing. Being cone shaped helps
- A waxy coating prevents water loss (chapstick?)
- Don’t freeze