November — Things that are green

Its November and everything is brown. Well, except for buckthorn, which is prominent as the last shrub with leaves. And those mosses over there are still lush and lovely. And a few sedges.

In fact, when you look a little more closely, quite a few species in the woods and prairies are still green in November. Take a look next time youre out — you may notice several fern species, club mosses, hepatica and others. Some of these actually remain green all through the winter, gathering light beneath the snow, ready to grow as soon as its gone.

Someone recently asked me, why do some species like buckthorn stay green so late in the season? Well, why not? In the world of botany, its all about adaptations that make a species best able to use available resources — light, water, nutrients — to survive. Some species have evolved to take advantage of the suns energy well after other species have gone dormant (or before others begin to grow in the spring). The early and late growers get the competitive advantage of those extra rays of energy. Some can also produce leaves before other species in the spring, thereby shading them out.

So why dont all plants do that? Apparently, for most species the adaptive advantage of having cold or freeze-tolerant leaves does not outweigh the cost. Theres a price to pay for keeping foliage on the plant at the edges of the season. To survive the freezing or near freezing temperatures, plants have to have special adaptations, such as sugars or other compounds that prevent the cells from freezing. Such compounds are generally costly to produce, requiring energy and nutrients. For most native species, the best strategy is to put resources into growing strong when the conditions are most favorable, rather than putting the extra resources into developing strategies to eke out a few extra photons at the beginning or end of the season.

Interestingly, non-native species that are most invasive tend to capitalize on this late/early season growing. Reed canary grass, common buckthorn, spotted knapweed, leafy spurge, cheatgrass, Kentucky bluegrass, garlic mustard, dandelion — all of these species are well-adapted to the cooler season. A benefit of this feature for ecological managers is that it makes those species easy to find and remove. Or if herbicide is used, it can be applied late in season with minimal harm to native species.

Find out more: Role of Cold-Responsive Genes in Plant Freezing Tolerance at the Plant Physiology web site.