Story by Virginia Barlow | Illustrations by Adelaide Tyrol
The Greens of Winter
Editor’s Note: For the last 22 years, Virginia Barlow has been looking up at the forest canopy and describing
the tree species she sees there. At long last, she’s run out of trees to profile. Fortunately for us, we’ve convinced her to
keep going by looking down. From here on out The Overstory will become The Understory, and Barlow will examine the
plants on the forest floor.
The forest understory is in some ways much easier to appreciate than the high-up leaves of the trees
that tower overhead. And some of the most beautiful plants between and among and below the shrubs,
seedlings, and saplings are the herbaceous ones. These plants lack woody stems and never get very tall,
so you can give your neck a rest by looking down instead of up.
Although the nonwoody plants of the understory account for less than three percent of the biomass of the forest, the role they play is far larger than that. Germination of the seeds of some tree
species is affected by herbaceous plants, and so is the survival of tree seedlings. Sometimes this effect
can be detrimental, as when certain ferns get too well established and form a dense carpet on the
forest floor, shading out young trees. But herbaceous plants often promote tree growth; when plants
die back in the fall or die never to return, their recycled leaves and roots supply nutrients to trees.
Trees in turn help out small plants during droughts by bringing water up with their deep taproots and
distributing it to their surface roots, where it is then available to small understory plants.
Like all other plants, understory ones need water and nutrients, but in the forest, it’s a lack of
light that usually limits their growth. The trees high above capture sunlight so efficiently that usually
only one to three percent of sunlight reaches the forest floor, but small plants use several different
strategies to adapt to the gloom.
One way to cope with the deep shade of a deciduous forest is to keep one’s leaves all winter. Some
winter leaves are produced in the summer, and though the plant is always green, a given leaf may
live for just less than a year. Leaves formed in summer detach soon after spring leaf-out. Nowadays,
plants that use this strategy are called wintergreens, and in our region, each leaf of a wintergreen has
an average lifespan of 39 weeks, in contrast to the 22 weeks of summer greens’ leaves. The ones called
evergreens really are always green, with an average leaf life of 85 weeks.
Wintergreen or evergreen, these brave little patches of green on the forest floor are somehow
reassuring – at least until snow falls and, again, before the rest of the world greens up in the spring.
Partridgeberry, Mitchella repens
The bright red berries of partridgeberry may be eaten by partridges, but as far as I
can tell, that doesn’t happen on a regular basis. They ripen in the fall, and I find that
many are still on the plant when it flowers the next spring. A lot goes into making
these bright red fruits and they may germinate and begin a new plant from time to
time, but more often partridgeberry plants grow vegetatively, each one spreading out and
living for a long time. Interestingly, it takes a pair of flowers to make one of these
unpalatable berries. Two white, four-petalled flowers arise from a common base,
and their ovaries fuse. As a result, each berry has two tiny spots on its surface.
Partridgeberry uses many tricks to get by in deep shade and on poor soil. This little
evergreen is as evergreen as a herbaceous plant gets: each leaf lives for an average of
120 weeks. Such a long leaf lifespan helps pay back the construction cost of a thick,
tough leaf, one that has lignin and other compounds that both help the leaf withstand
abrasion and discourage the likes of deer. “Repens” means creeping,
and its trailing vines lie right on the ground, so no investment in sup-
port structures is needed. It does most of its photosynthesizing in the
spring, before the forest canopy closes, and after trees’ leaves drop in
October. A shade-tolerant leaf simply can’t handle bright sun. Every
leaf functions best between a given minimum and maximum amounts
of sunlight. Partridgeberry’s leaves are at the bottom end of the scale: it can
grow in 0.4 percent sunlight and cannot use more than 7.0 percent sunlight