Pine savanna plant community disassembly after fire suppression

January 23, 2021

Biodiversity is being lost rapidly due to anthropogenic changes in land use, climate, and other environmental conditions. In fire-maintained ecosystems, altered fire regimes accelerate native species loss — community disassembly — and promote recruitment of fire-sensitive species. In this study, we ask whether fire suppression results in changes over time in functional trait composition of ground-layer species and whether these changes differ in longleaf pine savannas invaded by hardwoods from those invaded by sand pines. Location: Five Floridian locations on the southeastern coastal plain of the United States. At each location we selected a fire-maintained and fire-suppressed savanna and measured percent plant cover by ground-story species in 1,000 m2 plots. For 102 of these species, we measured 10 functional traits — height, growth form, specific leaf area, leaf dry matter content (LDMC), leaf water content, leaf ignition time, leaf mass consumed by fire, light compensation points (LCPs), non-structural carbohydrate concentrations in under-ground organs, and seed mass. Results: Fire exclusion was associated with reductions in both functional diversity and species richness. We identified 38 species exclusive to frequently burned sites: these species showed high LDMC values, high LCPs, high leaf mass consumed, and low leaf ignition time values. Lack of fire was associated with loss of 6 of the 12 C4 native grass species. Species and functional trait composition were affected by both time-since-fire and whether post-fire communities were invaded by broadleaved trees (Quercus spp. and Liquidambar styraciflua) or by sand pine (Pinus clausa). Conclusions: We demonstrated the effects of altered disturbance regimes on savanna plant species and functional trait composition. This trait-based approach advanced our understanding of how altered disturbance regimes can alter plant communities. Although 38 shade-intolerant and flammable native savanna species were absent by 10 years since fire, 12 such species persisted even 40 years after fire exclusion.