Disentangling Fragmentation Effects on Herbivory in Understory Plants of Longleaf Pine Savanna

Habitat fragmentation affects species and their interactions through intertwined

mechanisms that include changes to fragment area, shape, connectivity and distance to edge.

Disentangling these pathways is a fundamental challenge of landscape ecology and will help

identify ecological processes important for management of rare species or restoration of frag-

mented habitats. In a landscape experiment that manipulated connectivity, fragment shape, and

distance to edge while holding fragment area constant, we examined how fragmentation impacts

herbivory and growth of nine plant species in longleaf pine savanna. Probability of herbivory in

open habitat was strongly dependent on proximity to forest edge for every species, increasing

with distance to edge in six species (primarily grasses and annual forbs) and decreasing in three

species (perennial forbs and a shrub). In the two species of perennial forbs, these edge effects

were dependent on fragment shape; herbivory strongly decreased with distance to edge in frag-

ments of two shapes, but not in a third shape. For most species, however, probability of herbi-

vory was unrelated to connectivity or fragment shape. Growth was generally determined more

strongly by leaf herbivory than by distance to edge, fragment shape, or connectivity. Taken

together, these results demonstrate consistently strong edge effects on herbivory, one of the

most important biotic factors determining plant growth and demography. Our results contrast

with the generally inconsistent results of observational studies, likely because our experimental

approach enabled us to tease apart landscape processes that are typically confounded.