Title: Seedling recruitment factors in low-diversity Hawaiian wet forest: towards global comparisons among tropical forests
Author: Inman-Narahari, Faith; Ostertag, Rebecca; Cordell, Susan; Giardian, Christian P.; Kehauwealani, Nelson-Kaula; Sack, Lawren.
Source: Ecosphere 4(2):24. http://dx.doi.org/10.1890/ES12-00164.1.
Description: Seed arrival and habitat conditions (i.e., seed limitation and establishment limitation) are the primary drivers of community assembly in tropical forests. Several hypotheses make contradictory predictions for how the relative importance of these two drivers should vary with diversity. Particularly little is known of recruitment limitations in the regeneration of low diversity tropical forest. We quantified seed limitation, establishment limitation, seedling limitation, source limitation, dispersal limitation, and habitat associations using 2.5 years of seed rain and seedling distribution data collected within a 4-ha forest dynamics plot in extremely low diversity native-dominated Hawaiian wet forest. As a first approximation, we compared seedling recruitment limitations and the frequency of habitat associations across forests using the few available published data from high-diversity tropical forests employing similar methods and analyses. In Hawaiian wet forest, the relative importance of limitations varied greatly among species. Seed dispersal more strongly determined seedling recruitment than did establishment limitation across species, with 11 of 18 species completely seed limited (i.e., no seeds found). However, the most abundant species, Metrosideros polymorpha, was not seed limited, and regeneration of the three species with the highest seed production and dispersal was more strongly limited by habitat than seed arrival. Notably, although habitat associations may indicate niche specialization, Hawaiian species showed both significant habitat associations and niche overlap. On average across communities, seed and establishment limitations were strikingly similar across the three tropical forests compared, despite wide variations in diversity. Within all forests, species differed strongly in recruitment limitations, due to differences in species life history characteristics. Notably, while seed limitation in Hawaiian forests may be comparable to high-diversity tropical forests, the mechanisms driving this limitation may be different; i.e., loss of pollinators and dispersers and/or high seed predation, instead of the higher proportion of rare species that leads to high seed limitation in forests with greater diversity. Our first comparisons across forests indicated that the extent of habitat associations may be greater in lower-diversity forest, consistent with theory that proposes that lower species diversity increases the importance of habitat associations for community assembly.
Keywords: Center for Tropical Forest Science, dispersal limitation, establishment limitation, habitat association, Hawaii, USA, Metrosideros poly
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Inman-Narahari, Faith; Ostertag, Rebecca; Cordell, Susan; Giardian, Christian P.; Kehauwealani, Nelson-Kaula; Sack, Lawren. 2013. Seedling recruitment factors in low-diversity Hawaiian wet forest: towards global comparisons among tropical forests. Ecosphere 4(2):24. http://dx.doi.org/10.1890/ES12-00164.1.
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