Habitat fragmentation and loss can alter population dynamics, but understanding of how this plays out demographically remains incomplete for many taxa, and particularly for plants. A more mechanistic understanding of how fragmentation affects plant populations will require consideration of how particular landscape changes that accompany habitat loss and fragmentation influence key demographic rates, such as rates of recruitment. Here, we focus on how three factors associated with fragmentation (edge effects, patch isolation, patch edge:area) impact patterns of recruitment in two perennial forbs and two perennial grasses. Our work occurred within seven replicated, experimentally-fragmented landscapes. All habitat patches within each landscape have equal area and differ only in isolation (one is connected to a core area) and edge:area (high edge vs. low). We outplanted individuals of each study species at four distances from the edge, enabling examination of edge effects. We counted the number of recruits around 251 founder individuals of each of our species eight years post-introduction, to examine how our fragmentation factors impact long-term recruitment patterns. Our questions were: How is recruitment affected by: (1) edge proximity? (2) patch connectivity? (3) patch edge:area? We predicted less population growth under more fragmented conditions (near edges, in isolated patches, in high edge:area patches).
Results/Conclusions
(1) For one species, there were significantly more recruits at the edge of patches. For two species, there was a non-significant trend towards more recruits at the edge, while for the remaining species, there was a trend of more recruits far from edges. (2) Interestingly, three species had significantly or marginally significantly more recruits in isolated patches, while the fourth species had the opposite trend. (3) There was a trend in all four species towards fewer recruits in low edge:area ratio patches; this trend was statistically significant for two of the four. Overall, our findings generally differed from our predictions that the more fragmented conditions should have fewer recruits, though it is clear from our results that there are landscape-scale impacts of fragmentation on plant recruitment. Our results emphasize the need for additional research in understanding how and why population dynamics are altered in ecological systems with varying levels of fragmentation.