Prescribed fire is a powerful management tool in ecosystems that are dependent on regular disturbance. Where to burn, and especially how often to burn, are major decisions that can have long-term impacts on landscape structure and composition.
Recent research on prescribed fire at a commercial timber estate in South Africa gives new insight for where and how often burns should occur. Like other examples of managed lands with corridors, the Good Hope Estate in the Maputaland-Pondoland-Albany biodiversity hotspot includes patches of planted timber surrounded by a network of grasslands and indigenous forest. The native grassland ecosystem is fire-driven, so these corridors are burned regularly. However, not all corridors are burned at the same intervals, leading to a mosaic of successional stages with uncertain conservation value.
Biodiversity was assessed with butterfly surveys across five types of corridors that varied in size (small or large) and burn history (<1 yr ago, 1-2 yrs ago, 5+ yrs ago, and unburned indigenous forest). Over 2,000 individuals in 48 species were recorded, with species richness similar to that seen in native Afromontane grassland.
The results showed that butterfly species richness and assemblage differed significantly between seral stages. Overall, the best sites were those at the extreme stages along the successional gradient. The corridors with the highest biodiversity included recently burned grasslands (burned <1 yr ago) and unburned grasslands (burned 1-2 yrs ago), as well as corridors with indigenous mixed forest. The lowest biodiversity was found in mid-successional corridors that hadn’t been burned in 5-10 years, where thickets of tall grasses and significant woody encroachment had grown up to create a denser canopy.
In this type of ecosystem, prescribed fire may be most effective when used frequently or not at all, at least for managing biodiversity of invertebrates such as butterflies. The least effective management technique seems to be interrupting natural succession after grasslands have disappeared but before plant communities reach a climax stage. Conservation management can be a major challenge when it takes place in a highly dynamic system where regular fires are expected to occur. Each fire-dependent landscape has its own management goals, but knowing how other landscapes are best served by fire can help managers maximize conservation value in their own.
Gaigher, R., Pryke, J. S., and Samways, M. J. 2019. Divergent fire management leads to multiple beneficial outcomes for butterfly conservation in a production mosaic. Journal of Applied Ecology 56(6): 1322-1332.