Patterns and controls over biodiversity spillover around remnant longleaf pine woodland patches

Background/Question/Methods

Biodiversity conservation largely focuses on protected areas; however, recent work has suggested that the benefits of reserves may extend beyond their borders due to biodiversity spillover – the promotion of diversity in the non-target, matrix habitats surrounding reserves.  Spillover may represent a valuable conservation tool, yet little is known about the extent to which biodiversity spillover occurs around protected areas across landscapes, nor what factors might underlie site-to-site variation in levels of spillover.  We addressed these questions using a set of 29 remnant longleaf pine woodland patches in South Carolina.  We sampled understory plant communities to assess spillover within the post-agricultural pine plantation forest matrix around each remnant patch.  We then assessed the extent to which various site-level attributes predicted the overall level of spillover and the decay of spillover with distance from remnants into the matrix.

Results/Conclusions

Across all sites, we found evidence for a spillover effect.  Both understory species richness and similarity to remnant understory community composition were greatest in the matrix immediately adjacent to remnants.  Spillover levels declined with distance from remnants into the matrix (richness by 19-27%; compositional similarity by 12-26%) and rates of decay were greater for richness than compositional similarity.  Levels and rates of decay of spillover were predictable based on remnant and matrix attributes.  Levels of spillover richness were greatest at sites experiencing high frequency of prescribed fire management, whereas compositional similarity declined with remnant richness.  Decay of spillover richness was greatest at sites with high matrix canopy cover and at sites with high remnant richness, whereas declines in similarity with distance into matrix were greatest at sites with high levels of remnant richness.  These results suggest that plant biodiversity spillover may be a general pattern around remnant woodland patches, across a large managed plantation forest landscape.  The degree to which remnant longleaf pine woodland patches act as sources of spillover depends on both source diversity and permeability of the matrix.  Prescribed fire and overstory thinning – two common forest management tools in longleaf pine woodlands and plantations – may promote spillover around longleaf pine remnant patches both by increasing source diversity and by promoting matrix permeability.