Plants on Fire: Piedmont Savanna Stability, Resistance, and Resilience
Submitted by Johnny Randall, PhD, Associate Director for Natural Areas and Conservation Programs, North Carolina Botanical Garden, University of North Carolina at Chapel Hill
Ecosystem stability has been long debated in the theoretical and applied ecological literature and working through this is far beyond the scope of this article (and my brain capacity). Let me quickly add that stability is somewhat of a misnomer, since ecosystems are dynamic natural systems where change certainly occurs. The temporal element over which ecosystem stability operates is generally based on the principles of community resistance and resilience, which are at the heart of this concept and the subject of this article. Resistance is the ability of a community or ecosystem to avoid displacement after a disturbance or stressful period, whereas resilience is the ability to rebound or return to “normal” after a disturbance. And in our age of inevitable climate change, these concepts are particularly relevant and of great interest to ecologists and conservation biologists.
I am particularly interested in how climate change might affect our once and future Piedmont savanna communities (aka Piedmont prairie), which are typically remnants of this once extensive plant community. I have written before about the Piedmont savanna communities in this column, but want to reiterate that this is an incredibly rich ecosystem of approximately 300 plant species and a tremendous diversity of invertebrates (including insect pollinators), birds, and small mammals. The Piedmont savanna is also a shade-intolerant plant community, historically shaped by fire and large mammal grazing, that has found refuge along roadsides and other rights-of-way, where natural occurrences are few and far between.
Let me say right now that I am optimistic that the Piedmont savanna can hold its own against climate change through both resistance and resilience. My optimism comes from the fact that the incredibly drought tolerant Piedmont savanna flora has already responded to and persisted through past climate change events such as the severe droughts and temperature extremes of the Hypsithermal period (ca. 9,000-5,000 YBP). My concern comes from the fact that the present Piedmont savanna communities are relatively small, highly fragmented, and isolated from one another. (Island biogeography theory and related models show that such preserve characteristics lead to relatively rapid species extinctions.) But there is hope if these communities can be made healthy through proper preserve design and fire management (which will bolster resistance) and kept species rich and genetically diverse (which will facilitate resilience).
In order to accomplish our above mentioned "wellness plan" we must do the following: 1) make these preserves as large as possible, which means adding volume when the opportunity arises, 2) use regular prescribed fire as the primary management tool, 3) augment existing plant populations in each preserve (to help maintain genetic diversity), and 4) plant appropriate species that do not currently occur (but presumably did once occur) in each preserve.
I am also optimistic because we have had very encouraging results from fire management across the Piedmont ecoregion, our native seed programs are booming, and more and more people are taking interest in restoring the Piedmont savanna. We certainly have our work cut out for us – but as my father says – can’t never did nothin'…