Higher β‐diversity observed for herbs over woody plants is driven by stronger habitat filtering in a tropical understory

Abstract

Herbaceous plants are a key component of tropical forests. Previous work indicates that herbs contribute substantially to the species richness of tropical plant communities. However, the processes structuring tropical herb diversity, and how they contrast with woody communities, have been underexplored. Within the understory of a 50-ha forest dynamics plot in central Panama, we compared the diversity, distribution, and abundance of vascular herbaceous plants with woody seedlings (i.e., tree and lianas <1 cm DBH and ≥20 cm tall). Beta-diversity was calculated for each community using a null model approach. We then assessed the similarity in alpha and beta-diversity among herbs, tree seedlings, and liana seedlings. Strengths of habitat associations were measured using permutational ANOVA among topographic habitat-types. Variance partitioning was then used to quantify the amount of variation in species richness and composition explained by spatial and environmental variables (i.e., topography, soils, and shade) for each growth form. Species richness and diversity were highest for tree seedlings, followed by liana seedlings and then herbs. In contrast, beta-diversity was 16-127% higher for herbs compared to woody seedlings, indicating higher spatial variation in this stratum. We observed no correlation between local richness or compositional uniqueness of herbs and woody seedlings across sites, indicating that different processes control the spatial patterns of woody and herbaceous diversity and composition. Habitat associations were strongest for herbs, as indicated by greater compositional dissimilarity among habitat types. Likewise, environmental variables explained a larger proportion of the variation in species richness and composition for herbs than for woody seedlings (richness = 25%, 14%, 12%; composition = 25%, 9%, 6%, for herbs, trees, and lianas, respectively). These differences between strata did not appear to be due to differences in lifespan alone, based on data from adult trees. Our results point to contrasting assembly mechanisms for herbaceous and woody communities, with herbs showing stronger niche-derived structure. Future research on tropical herbaceous communities is likely to yield new insights into the many processes structuring diverse plant communities.

Forest community assembly is driven by different strata‐dependent mechanisms along an elevational gradient

“…It is expected that soil resources could be related to the composition and diversity of plant communities, and that this could be stronger for the understorey due to limiting soil resources (Gilbert & Lechowicz, ; Murphy et al, ). As expected, our results showed that soil properties were significant predictors for the phylogenetic diversity of shrubs and the functional diversity of herbs.…”

Edge effects reduce α‐diversity but not β‐diversity during community assembly in a human‐modified tropical forest

“…Indeed, seedling communities within 60‐m of edges were primarily structured by species turnover, suggesting strong species–environment relationships (Murphy et al. ). In addition, given that dispersal limitation is an inherent feature of many tropical forests (Wright et al.…”

“…, Murphy et al. ) can lead to high β‐diversity via increased spatial turnover in local assemblages. With fragmentation however, sites near edges may become compositionally similar because higher ambient temperatures, desiccation, and litter fall at edges create stresses that lead to similar tree species recruiting at different sites.…”

“…Higher b-diversity suggests community differentiation and lower b-diversity signals homogenization (Socolar et al 2016). In tropical forests, dispersal limitation, microhabitat variation, or predators and pathogens (Nathan and Muller-Landau 2000, Bagchi et al 2014, Murphy et al 2016 can lead to high b-diversity via increased spatial turnover in local assemblages. With fragmentation however, sites near edges may become compositionally similar because higher ambient temperatures, desiccation, and litter fall at edges create stresses that lead to similar tree species recruiting at different sites.…”

DNA barcoding herbaceous and woody plant species at a subalpine forest dynamics plot in Southwest China

“…Herbaceous plants contribute substantially to the diversity and abundance of forests ecosystems, particularly in temperate regions (Gilliam, 2007(Gilliam, , 2014Luo et al, 2016aLuo et al, , 2016bWang, Tang & Fang, 2007). However, interactions between herbaceous and woody plant layers in community assemblages have long been neglected in forest dynamics models, even though it is widely known that herbaceous species can impact the regeneration of tree species (Murphy, Salpeter & Comita, 2016;Thrippleton, Bugmann, Kramer-Priewasser & Snell, 2016). DNA barcoding has mainly been used for tree species in forest dynamic plots of tropical, subtropical, and temperate regions (Erickson et al, 2014;Kress et al, 2009;Pei et al, 2015).…”