Fire management strategies to maintain species population processes in a fragmented landscape of fire‐interval extremes

Abstract

Changed fire regimes have led to declines of fire-regime-adapted species and loss of biodiversity globally. Fire affects population processes of growth, reproduction, and dispersal in different ways, but there is little guidance about the best fire regime(s) to maintain species population processes in fire-prone ecosystems. We use a process-based approach to determine the best range of fire intervals for keystone plant species in a highly modified Mediterranean ecosystem in southwestern Australia where current fire regimes vary. In highly fragmented areas, fires are few due to limited ignitions and active suppression of wildfire on private land, while in highly connected protected areas fires are frequent and extensive. Using matrix population models, we predict population growth of seven Banksia species under different environmental conditions and patch connectivity, and evaluate the sensitivity of species survival to different fire management strategies and burning intervals. We discover that contrasting, complementary patterns of species life-histories with time since fire result in no single best fire regime. All strategies result in the local patch extinction of at least one species. A small number of burning strategies secure complementary species sets depending on connectivity and post-fire growing conditions. A strategy of no fire always leads to fewer species persisting than prescribed fire or random wildfire, while too-frequent or too-rare burning regimes lead to the possible local extinction of all species. In low landscape connectivity, we find a smaller range of suitable fire intervals, and strategies of prescribed or random burning result in a lower number of species with positive growth rates after 100 years on average compared with burning high connectivity patches. Prescribed fire may reduce or increase extinction risk when applied in combination with wildfire depending on patch connectivity. Poor growing conditions result in a significantly reduced number of species exhibiting positive growth rates after 100 years of management. By exploring the consequences of managing fire, we are able to identify which species are likely to disappear under a given fire regime. Identifying the appropriate complementarity of fire intervals, and their species-specific as well as community-level consequences, is crucial to reduce local extinctions of species in fragmented fire-prone landscapes.

Using ideal distributions of the time since habitat was disturbed to build metrics for evaluating landscape condition

“…, Tulloch et al. ). Here we set the benchmark as the mean “tolerable” TSLD for the target community or species.…”

“…, Tulloch et al. ). Because it is unlikely that the system has a single optimal age‐class distribution (Gosper et al.…”

“…In relatively intact landscapes, predominantly public reserves, unplanned fires burn large tracts of native vegetation at high frequencies (e.g., every 8 yr; Tulloch et al. ), whereas in isolated remnants in the agricultural zone, fire is prevented or suppressed by farmers to protect crops (O'Donnell et al. , Parsons and Gosper , Gill et al.…”

“…, Tulloch et al. ). Using this knowledge, studies such as the U.S. interagency LANDFIRE program have quantified the dissimilarity between an ecological system's current condition and its natural range of variability with respect to a benchmark (Rollins ).…”

“…Our approach provides a simple way to evaluate the impact of disturbances that affect vegetation condition, such as degradation of vegetation structure and altered composition as vulnerable species are replaced by species tolerant to, or unaffected by, disturbance (Tulloch et al. ).…”