Controls over understory species richness within degraded remnants of longleaf pine woodland

Background/Question/Methods

Isolation and fragmentation of remnant habitats can influence the diversity of understory plant communities, and land-use history and forest management can contribute to among-patch variability of species composition in these degraded habitats.  Understanding the factors that drive understory diversity in remnant patches could inform management efforts focused on the restoration of longleaf pine habitat.  We evaluated both local and landscape-level factors potentially contributing to the variability of understory richness within remnant longleaf pine woodland in South Carolina.  We surveyed understory plant communities in 29 remnant patches of longleaf pine woodland and assessed variability of total species richness (R_T) and richness of only longleaf pine associates (R_A) among sites using patch area and shape, current management, and physical variables as predictors.

Results/Conclusions

Total species richness (51-133 species) and the richness of remnant associates (12-44 species) varied considerably across sites.  The amount of remnant habitat within 100-m, 200-m, and 300-m buffers surrounding the plots was not a significant predictor of this variability, nor was the amount of habitat edge: area.  Although the number of burns in the past four decades was positively associated with total richness within remnants, the best model included only duff layer depth(D) and percent pine basal area (P; R_T = 117-16.9D+31.2P, R²=0.41).  Similarly, richness of remnant associates was predictable only by the depth of the duff layer (R_A = 44-6.2D, R²=.34).  Although fire history was not retained in the best models, duff depth was highly correlated with fire history, suggesting that fire frequency promotes richness in these remnant patches of longleaf pine woodland by reducing barriers to establishment.  Further, the positive association of richness to pines in the canopy suggests that pine litter may limit seedling establishment less than hardwood litter. Ultimately, local rather than landscape level factors were the best predictor s of species richness in this study.  Frequent burns and the promotion of a pine overstory may increase diversity in remnant patches of longleaf pine woodlands.