Changes in habitat structure and spider community composition in response to experimental woodland restoration in northern Mississippi

Background/Question/Methods

Decades of fire suppression have radically altered the uplands of northern Mississippi. Once blanketed by grassy open oak woodlands, this region is now experiencing mesophytic tree invasion, canopy closure, reduced oak regeneration, and herbaceous understory loss. In an attempt to reestablish historical conditions, experimental restoration has been initiated through thinning and prescribed burn treatments. Our research, part of a comprehensive monitoring program, strived to determine the impact of woodland restoration on both habitat structure and spider community. Spiders are excellent candidates for monitoring efforts due to the relative ease in which they can be sampled and identified, their links to many food chains, and their sensitivity to changes in habitat structure. We predicted that spider community composition of the treatment site would be markedly diverse, as well as intermediate between that of forest and field ecosystems, reflecting a transitional habitat structure. To test our predictions, habitat structure and spider community were sampled within four habitats located at the restoration site: fire-suppressed forest, moderately treated forest, intensely treated forest, and old field. Canopy openness, litter cover/depth, and vegetation cover/density were measured within each sample site. Spiders were collected by ground searches, aerial/beat searches, sweep-netting, night searches, and pitfall traps.

Results/Conclusions

The intense treatment was found to harbor the highest spider diversity, a value significantly greater than that of the fire-suppressed forest and old field, but not the moderate treatment. Although treatments resulted in architecture more typical of open habitats, such as increased density of herbaceous vegetation and reduced leaf litter cover, the predicted magnitude of transitional habitat structure failed to develop. Since herbaceous vegetation existed in patches that were primarily associated with natural tree falls, it is recommended that a higher intensity of thinning be administered. A distinct difference was observed between the old field and forested habitats in respect to vegetation structure, spider community composition, and spider guild proportions. Rather than generate an intermediate spider community, the treatments resulted in a unique assemblage that shared many species with the fire-suppressed forest. This assemblage diverged from the fire-suppressed forest through changes in the proportions of shared species, loss of species, addition of unique species, and inclusion of select old field species. This study indicates that subjecting landscapes to a mosaic of fire regimes will likely enhance spider diversity through the formation of varied structural environments.