Summer has begun and in the northern hemisphere that usually means hot and sunny especially if trails are above tree line. But in the northeastern United States we are lucky that miles and miles of hiking trails remain well shaded as they traverse forests under a canopy of millions of maple. birch, hickory, oak and beech leaves, among others. The shade is a balm on a hot and sunny day.
Running through a shady trail last week, I thought about the challenges of life in the shadows. For plant and tree life dependent on sunlight for photosynthesis, shade would seem to a be a punishment, like half rations for a prisoner, or no rations at all. Yet, the understory of forests, the part that is mostly in the shade, does teem with verdant greenery. Indeed, some trees, notably the striped maple, inhabit only the understory and do not ever breech the forest canopy. Other trees, however, are shade tolerant. That is, they can survive in the shade, for years if needed, until they have an opportunity to leave the understory and poke their tallest limbs into sunlight, perhaps after a nearby taller tree topples over, clearing a space in the forest canopy. And, many plants, even in our own gardens, flourish only in the shade.
How does life tolerate the dimness of the daytime darkness, the absence of direct sunlight, especially when that light is a currency of life for most plants and trees? There is no one answer. Instead, plants in the shade use a cornucopia of adaptations for their survival.
Think of common shade plant in many home gardens, Hostas. Notice that they have large leaves, an adaptation to collect as much sunlight as possible. In addition, the chloroplasts in the leaves of shade dwelling plants and trees are larger than in trees and plants that live in full light and their epidermal cells are better designed to maximize light. Also, shade trees and plants have no waxy layer on their leaves, something that trees in full light use to help reflect away unneeded light. And, in addition, shaded plants can change the angle of their leaves to maximize any available light during the day.
Shade is not only sunlight blocked, but rather potential not yet realized, growth untapped, waiting for opportunity. Shade tolerant plants, though, have it figured out. Do not wither during lean times. Adapt and be patient. If you find yourself struggling out on your trail, peer into the shade for inspiration, then continue on your way.
The sunlight, it is a coming.
Howard E. Friedman
(for more information about shade apaptations, visit : http://plantsinaction.science.uq.edu.au)