Wiregrass (Aristida beyrichiana) survival and reproduction after fire in a long-unburned pine savanna

Abstract

Restoring fire regimes is a major goal of biodiversity conservation efforts in fire-prone ecosystems from which fire has been excluded. In the southeastern U.S.A., nearly a century of fire exclusion in pine savannas has led to significant biodiversity declines in one of the most species-rich ecosystems of North America. In these savannas, frequent fires that support biodiversity are driven by vegetation-fire feedbacks. Understory grasses are key components of these feedbacks, fueling the spread of fires that keep tree density low and maintain a high-light environment. When fire is reintroduced to long-unburned sites, however, remnant populations of bunchgrasses might experience high mortality from fuel accumulation during periods of fire exclusion. Our objective was to quantify fire effects on wiregrass (Aristida beyrichiana), a key component of vegetation-fire feedbacks, following 16 years without fire in a dry pine savanna typically considered to burn every 1-3 years. We examined how wiregrass size and fuel (duff depth and presence of pinecones) affected post-fire survival, inflorescence and seed production, and seed germination. Wiregrass exhibited high survival regardless of size or fuels. Probability of flowering and inflorescence number per plant were unaffected by fuel treatments but increased significantly with plant size (p = 0.016). Germination of filled seeds was consistent (29-43%) regardless of fuels, although plants in low duff produced the greatest proportion of filled seeds. The ability of bunchgrasses to persist and reproduce following fire exclusion could jumpstart efforts to reinstate frequent-fire regimes and facilitate biodiversity restoration where remnant bunchgrass populations remain.

Fig 1. Study system and treatments.

Wiregrass a) in the understory of a long unburned xeric pine savanna with an overstory dominated by longleaf pine and turkey oaks; b) under three pinecones for the low duff plus added pinecones treatment (LD + P); and c) after the reintroduction fire, with a portion of the plant resprouting (pen placed for size reference).

Fig 2. Probability of reproduction (inflorescence production) by wiregrass (Aristida beyrichiana) plants.

Individuals were subject to different fuel treatments during a reintroduction fire in a long-unburned pine savanna. Probability of reproduction increased with size. There were no significant differences between individual treatments.