Updating models for restoration and management of fiery ecosystems

Abstract

Scientific models that guide restoration/management protocols should be reviewed periodically as new data become available. We examine ecological concepts used to guide restoration of pine savannas and woodlands, historically prominent but now rare habitats in the southern North American Coastal Plain. For many decades, pine savanna management has been guided predominantly by a biome-centric succession model. Pine savannas have been considered earlysuccessional communities that, in the absence of fire, transition rapidly toward closed-canopy hardwood forests. Recurrent fires have been viewed as exogenous disturbances that maintain savanna ecosystems as a sub-climax, blocking succession to an equilibrium steady state (closedcanopy forests). Over recent decades, a vegetation-fire feedback model has emerged in which pine savannas are conceptualized as persistent, non-equilibrium communities maintained by endogenous, co-evolutionary vegetation-fire feedbacks. Endemic plant species are resistant to fires and specialized for post-fire conditions generated by frequent lightning fires, primarily within a distinct fire season. These species produce pyrogenic fine fuels that are easily ignited.The resulting fire regimes, entrained by these vegetation-fire feedbacks, are predicted to result in persistent pine savannas. Local variation over space and time in evolutionary feedback mechanisms between pyrogenic vegetation and fire regimes produces heterogeneous landscapes.Disturbances of these feedbacks, such as human fire suppression, are postulated to result in rapid transition to communities lacking feedback elements, such as closed-canopy forest and those without pyrogenic species. Succession-based management focuses on reversing the transition to forest, primarily by removing hardwoods and reintroducing fire as a disturbance. However, we advocate restoration and management approaches that target reinstitution of functional vegetation-fire feedbacks. Such approaches should favor native pyrogenic plant species and 3 reinstitute fire regimes that mimic historical, evolutionarily derived fire regimes. Vegetation-fire feedback concepts should be useful in addressing resistance and resilience of fiery ecosystems worldwide to inherent changes in feedback mechanisms, constituting a framework useful in addressing global management challenges.

Pyrogenic fuels produced by savanna trees can engineer humid savannas

“…, Fill et al. , Bond ). In these savannas, lightning ignited fires characteristically burn ground‐layer vegetation during annually predictable fire seasons.…”

“…, ), and so increases in densities might result in “woodlands” as one extreme of a continuum in savanna tree density (Fill et al. ). In such cases, fuels shed beneath and around savanna trees could replace those fuels normally provided by grasses.…”

The effects of vegetative type, edges, fire history, rainfall, and management in fire‐maintained habitat

“…Burning during the best season to stimulate grasses and promote fire spread might be advantageous (Fill et al. ), but fire managers in our study sites had extreme limitations regarding meteorological and operational constraints that made burning only during the dry‐to‐wet transitional season (e.g., May) difficult. Cutting was an expensive tool, and it may be unreasonable to remove most forest edges and edges associated with human landscape features so that prioritization of management efforts becomes necessary.…”

Clarifying the confusion: old-growth savannahs and tropical ecosystem degradation

“…Recognition of the drivers of tropical savannah degradation is important to improve their conservation. Most savannahs are dependent on frequent fires and/or megafaunal herbivory, forces that are part of the internal ecological dynamics of savannahs, rather than externally imposed disturbances [9,50]. Although in pre-human history, savannah fires were ignited by lightning strikes, in most of the world's savannahs, humans are now the primary sources of ignitions [2,51,52].…”

“…For the forest portions of these models, ecological states, associated terminology and causes of degradation are well established [42]. For savannahs, degradation terminology is less clearly established, in part because fire-dependent savannahs have only recently begun to be conceptualized as non-successional systems [1,9,50]. To facilitate communication among forest and savannah ecologists, the terminology I use for savannah ecosystem states (figure 1) reflects analogous forest degradation terms and the savannah conservation literature.…”