Clarifying the role of fire in the deciduous forests of eastern North America: reply to Matlack

Fire Season, Overstory Density and Groundcover Composition Affect Understory Hardwood Sprout Demography in Longleaf Pine Woodlands

Seasonal timing of prescribed fire and alterations to the structure and composition of fuels in savannas and woodlands can release understory hardwoods, potentially resulting in a global increase of closed-canopy forest and a loss of biodiversity. We hypothesized that growing-season fire, high overstory density, and wiregrass presence in longleaf pine woodlands would reduce the number and stature of understory hardwoods, and that because evergreen hardwoods retain live leaves, dormant-season fire would reduce performance and survival of evergreen more than deciduous hardwoods. Understory hardwood survival and height were monitored over seven years in longleaf pine woodlands in southwest Georgia with a range of overstory density, groundcover composition, and season of application of prescribed fire. Hardwood stem survival decreased with increasing overstory density, and deciduous hardwoods were more abundant in the absence of wiregrass. Contrary to expectations, evergreen hardwood growth increased following dormant-season fire. Differences in hardwood stem survival and height suggest that low fire intensity in areas with low overstory density increase the risk that hardwoods will grow out of the understory. These results indicate a need for focused research into the effects of groundcover composition on hardwood stem dynamics and emphasize that adequate overstory density is important in longleaf ecosystem management.

A critique of the historical-fire-regime concept in conservation

Prescribed fire is widely accepted as a conservation tool because fire is essential to the maintenance of native biodiversity in many terrestrial communities. Approaches to this land-management technique vary greatly among continents, and sharing knowledge internationally can inform application of prescribed fire worldwide. In North America, decisions about how and when to apply prescribed fire are typically based on the historical-fire-regime concept (HFRC), which holds that replicating the pattern of fires ignited by lightning or preindustrial humans best promotes native species in fire-prone regions. The HFRC rests on 3 assumptions: it is possible to infer historical fire regimes accurately; fire-suppressed communities are ecologically degraded; and reinstating historical fire regimes is the best course of action despite the global shift toward novel abiotic and biotic conditions. We examined the underpinnings of these assumptions by conducting a literature review on the use of historical fire regimes to inform the application of prescribed fire. We found that the practice of inferring historical fire regimes for entire regions or ecosystems often entails substantial uncertainty and can yield equivocal results; ecological outcomes of fire suppression are complex and may not equate to degradation, depending on the ecosystem and context; and habitat fragmentation, invasive species, and other modern factors can interact with fire to produce novel and in some cases negative ecological outcomes. It is therefore unlikely that all 3 assumptions will be fully upheld for any landscape in which prescribed fire is being applied. Although the HFRC is a valuable starting point, it should not be viewed as the sole basis for developing prescribed fire programs. Rather, fire prescriptions should also account for other specific, measurable ecological parameters on a case-by-case basis. To best achieve conservation goals, researchers should seek to understand contemporary fire-biota interactions across trophic levels, functional groups, spatial and temporal scales, and management contexts.