For almost 100 years plant ecologists have noticed that in some species, plants that seem to die come back two or more years after their last appearance. John Harper, the pioneering ecologist who set the stage for modern plant ecology with his writings on evolutionary approaches to studying the Plant Kingdom and his now quintessential textbook on plant population ecology, suggested that these plants seemed to defy the finality of death, and that clearly this could not be so. Rather than being resurrected from the dead, these orchids and other long-lived herbaceous plants actually live underground without sprouting for years at a time, in a state referred to as “vegetative dormancy”. By not sprouting, they also do not photosynthesize, nor do they flower and reproduce, seemingly defying the very definition of a plant.
I first encountered my first dormancy-prone species in Cypripedium parviflorum, the small yellow lady’s slipper, as someone charged in helping to manage it. This rare species is of conservation concern, as are so many other dormancy-prone species. Although these species are of conservation concern because of the destruction of their habitat due to farming and suburban expansion, conservation management plans often include little provision for active management because the ecologies of these species are not well understood. One particular problem is that the ecology of vegetative dormancy is not well understood, and so it is difficult to manage a species that undergoes it. For example, is dormancy a sign that the plant is weakening and dying? Or is it a buffer against environmental stress? Is it adaptive, or not?
Many hypotheses have been explored for why and how vegetative dormancy occurs. In our article, we present the first strong evidence that this phenomenon is actually due to the long-term cost of high growth to survival, because high growth sometimes leads to a shortage of stored energy reserves that can exacerbate mortality in harsh years. This is important, since dormancy-prone species are often rare and endangered, and an accurate understanding of their life histories is required to understand their population dynamics. Ultimately, without this understanding, we cannot develop effective management plants for them.
Our next step in this research is to see how general this pattern is – is dormancy so common for the same reason in other species, or has it evolved for a number of reasons across the Plant Kingdom? Our own suspicion is that if dormancy is always adaptive, then the reason for it is likely to change with important ecological or life history characteristics, such as lifespan, mode of reproduction, and growth form.
“Life-history costs make perfect sprouting maladaptive in two herbaceous perennials” by Shefferson, Warren II & Pulliam. The paper is currently in Early View.