When landscape corridors restore plant dispersal relative to unfragmented landsapes
Dispersal of seeds, especially over long distances, is important for mediating plant population, community, and evolutionary dynamics. Habitat fragmentation can create significant impediments to dispersal. Where habitats are fragmented, landscape corridors can increase dispersal, yet the degree to which corridors restore levels of dispersal to those observed in unfragmented landscapes remains unknown. To test the effects of corridors in restoring dispersal to levels found in unfragmented landscapes, we compared seed dispersal patterns of four species in twelve landscapes, four with unfragmented habitat and eight with experimentally fragmented habitat patches connected by corridors. We further considered whether species' responses varied with seed dispersal mode, a trait that correlates with dispersal capacity and responses to fragmentation, by testing the role of corridors in restoring dispersal of two wind and two bird-dispersed plants. We constructed dispersal kernels in unfragmented and corridor-connected landscapes for these species by using 15N isotopes to mark seeds in the center of each landscape and recovering marked seeds in seed traps at distances up to 200 m.
For the two wind-dispersed plants, seed dispersal kernels were similar in landscapes connected by corridors and in unfragmented landscapes. In contrast, dispersal kernels of bird-dispersed seeds differed between species: Morella cerifera experienced less and Rhus copallina more long-distance dispersal in corridor-connected than in unfragmented landscapes. Our findings highlight the feasibility and utility of using community-level marking techniques for simultaneous quantification of dispersal dynamics of multiple species. We further demonstrate that corridors can restore levels of connectivity to those of unfragmented landscapes, but also highlight that this effect varies among species in ways that may be related to dispersal traits.