Abstract
Considerable areas dominated by bracken Pteridium aquilinum (L.) Kuhn occur worldwide and are associated with arrested forest recovery. How forest recovery is impeded in these areas remains poorly understood, especially in the African highlands. The component processes that can lead to recruitment limitation—including low seed arrival, availability and persistence—are important determinants of plant communities and offer a potential explanation for bracken persistence. We investigated key processes that can contribute to recruitment limitation in bracken‐dominated clearings in the Bwindi Impenetrable National Park, Uganda. We examined if differences in seed rain (dispersal limitation), soil seed bank, or seed removal (seed viability and persistence) can, individually or in combination, explain the differences in tree regeneration found between bracken‐dominated areas and the neighboring forest. These processes were assessed along ten 50‐m transects crossing the forest–bracken boundary. When compared to the neighboring forest, bracken clearings had fewer seedlings (bracken 11,557 ± 5482 vs. forest 34,515 ± 6066 seedlings/ha), lower seed rain (949 ± 582 vs. 1605 ± 335 tree seeds m−2 year−1), comparable but sparse soil seed bank (304 ± 236 vs. 264 ± 99 viable tree seeds/m2), higher seed removal (70.1% ± 2.4% vs. 40.6% ± 2.4% over a 3‐day interval), and markedly higher rodent densities (25.7 ± 5.4 vs. 5.0 ± 1.6 rodents per 100 trapping sessions). Camera traps revealed that rodents were the dominant animals visiting the seeds in our seed removal study. Synthesis: Recruitment limitation contributes to both the slow recovery of forest in bracken‐dominated areas, and to the composition of the tree species that occur. Low seed arrival and low persistence of unburied seeds can both explain the reduced density of seedlings found in bracken versus neighboring forest. Seed removal, likely due to rodents, in particular appears sufficient to constrain forest recovery and impacts some species more severely than others.
Highlights
The role of clearings dominated by bracken fern Pteridium aquilinum (L.) Kuhn in retarding forest recovery is a worldwide concern
We focus on the early life-history stages where recruitment limitation can be manifested, that is, seed arrival, seed persistence, and seed removal
In this study, using a series of integrated field studies, we explored the role of recruitment limitation in explaining the difference in regeneration between bracken and neighboring forest environments by examining seedling densities, seed rain, soil seed bank, and seed removal rates
Summary
The role of clearings dominated by bracken fern Pteridium aquilinum (L.) Kuhn in retarding forest recovery is a worldwide concern. In this study, using a series of integrated field studies, we explored the role of recruitment limitation in explaining the difference in regeneration between bracken and neighboring forest environments by examining seedling densities, seed rain, soil seed bank, and seed removal rates (and rodent densities). Given that these limitations will favor or filter species in a manner that may shed light on the underlying processes, we are interested in both the implications for overall woody regeneration and the differences that arise among individual species
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