I write this column under the optimistic assumption that the Drought of 2022 is in the rear-view mirror. September and the first half of October brought some serious rain to the Vineyard, mitigating the effects of one of the driest summers in recent memory. July and August were essentially rainless, and in the natural world, plants and animals had to rely on water they had already stored, what they could draw from diminished groundwater and surface water, or what they could absorb from condensation or from their food.
The drought was unequivocally stressful for many species, though my reaction, in retrospect, is that wildlife in general fared better than I might have expected. The fact is that this was not the first drought in the Vineyard’s history, nor, probably, even the worst. Even a normal Vineyard summer usually includes significant periods without rain. And over thousands of generations, every wild species that lives here has had to evolve strategies for dealing with a short-term dearth of water.
I should be clear that in using a word like “strategies,” I don’t mean anything volitional. But droughts exert a powerful selective force on wild populations. Genes, and more to the point, the physiological expression of genes that aid survival grow more prevalent. And over time, each species evolves what amounts to a sort of unconscious collective wisdom, helping as many individuals as possible endure the difficult conditions.
During any kind of stress, a plant or animal needs to balance basic things: its own survival and its ability to reproduce. Because reproduction is a resource-intensive process, these two goals are often at odds with each other. From an evolutionary perspective, a drought poses the question “Should I conserve water for my own survival, or should I expend it in the form of seeds or offspring?”
For many of our native perennial plants, I think the answer is “save yourself.” Even notoriously drought-resistant plants like little bluestem grass, with its deep root system and narrow, water-hoarding leaves, had something of an off year in 2022, producing relatively little vegetative growth and then turning out a light crop of seed. A clump of bluestem can live for decades, though; it will simply try again in 2023. There’s no need for plants like that to take chances with high reproductive activity in a drought year.
Some plants play a different game altogether: Hunker down, endure the summer, and schedule your flowering to coincide with the early autumn shift to a wetter regime. The white heath aster in my yard, for example, burst into bloom at the end of September, powered by the rains of recent weeks and showing no sign at all of the summer’s drought. The same with stiff aster. Both plants have evolved small, tough leaves that lose little water to evaporation, getting them through the summer poised to exploit autumnal rain during their late-season bloom periods. This plan can be expected to work for as long as the seasonal pattern of our rainfall persists.
While plants may experience the most direct effects of a drought, they pass those effects on to the insects and other animals that feed on them. Many of those insects, accordingly, had a poor year in 2022. Numbers of most Orthoptera species, most of which have a season-long life cycle and all of which feed primarily on plants, were conspicuously low this year. I surmise that Orthoptera nymphs, hatching out into dry conditions and stunted vegetation, lacked the fast-growing, tender, and nutritious food that they require for optimal development. Or perhaps they simply dehydrated. Butterflies, likewise, were scarce almost across the board, and probably for the same reasons.
There were exceptions, though. I wrote earlier this year about the abundance of tiger swallowtails, surprising in a generally poor year for butterflies. And among Orthoptera, the jumping bush cricket, Hapithus saltator, is present in bumper crop numbers. The reason? I don’t know for sure, but it’s interesting that both tiger swallowtails and jumping bush crickets associate with trees instead of herbaceous vegetation. Perhaps the deep root systems of large, woody plants, allowing access to groundwater even in dry years, indirectly subsidized a tree-loving subset of insects.
Amid the stories of resilience and even success, there are examples of failure. Bracken fern, for example, really struggled this season, with many individuals dry and inert as early as late July. I doubt many of these plants are actually dead. But with their abbreviated growing season, they ceded space and resources to hardier competitors. And the bracken will likely start next season somewhat depleted as a result of its disastrous summer. Over time, if the trend toward longer, more frequent, and more intense droughts continues, this may be a species that will grow less prevalent.
But as for the Vineyard ecosystem as a whole, I’m optimistic. Droughts are bottleneck events, for sure, winnowing out individuals and eventually even species that are poorly suited to enduring dryness. But nature is resourceful, and while a drier future would surely change things, surprising numbers of our native species have tricks up their sleeves for surviving.
