Seed rain along a gradient of degradation in Caribbean dry forest: Effects of dispersal limitation on the trajectory of forest recovery.

Questions: Tropical dry forests that experience severe disturbances (e.g., fires) often remain degraded for long time periods, during which non‐native grasses and trees dominate. One barrier to native tree regeneration in degraded areas may be seed dispersal limitation. To better understand how dispersal limitation influences recovery from degradation, we tested whether the mode and rates of seed dispersal differed in degraded sites dominated either by the exotic tree Leucaena leucocephala or open areas dominated by introduced pasture grasses. We also tested whether L. leucocephala stands facilitate the recruitment of native trees by increasing their seed input compared to open grass areas. Location: Guánica Commonwealth Forest, Puerto Rico. Methods: Seed rain was measured for one year in traps located within five vegetation types that ranged in degree of forest degradation from open grass to intact native forest. Results: In open grass areas, seed rain density was similarly low for L. leucocephala and abiotically dispersed native trees (mean [95% CI] = 50.9 [15.1–171.0] vs. 34.2 [10.3–113.5] seeds m−2 year−1), whereas it was even lower for animal‐dispersed native trees (0.14 [0.03–0.67] seeds m−2 year−1). Compared to open grass areas, L. leucocephala‐dominated stands, even those with grass understories, had higher seed rain density of animal‐dispersed trees (43.0 [12.9–143.6] seeds m−2 year−1), but not abiotically dispersed trees (20.8 [6.3–68.5] seeds m−2 year−1). Conclusions: The dominance of L. leucocephala in disturbed Caribbean dry forests does not appear to be mediated by disproportionate seed arrival in open areas compared to native tree seeds. Rather, subsequent factors such as seed and seedling survival likely favor L. leucocephala in highly degraded areas. Since L. leucocephala stands increase the seed rain of animal‐dispersed native trees, retaining them in highly disturbed Caribbean dry forests may facilitate the regeneration of native forests. [ABSTRACT FROM AUTHOR]