Abstract
AbstractQuestionsDo composition and richness of woody plants differ between gaps and closed canopy in subtropical forests, and does this difference vary across life stages of tree species? Is tree species richness in gaps a function of regeneration density?LocationSubtropical Shorea robusta Gaertn (Sal) forest, central Nepal.MethodsWe collected vegetation data from two old‐growth S. robusta forest stands. We sampled 128 plots of 100 m2 equally spread between the two habitats: gap and closed canopy. In each plot, we recorded the total number of woody species, number of individuals of seedlings and saplings of tree species and measured the DBH of all saplings. We compared species richness and composition of total woody species, seedlings and saplings between the two habitats. We used ordination to analyse species composition, and an individual‐based species accumulation curves to illustrate the effect of density on species richness.ResultsThe species composition of total woody species and seedlings was similar in both habitats, but species composition of saplings differed between habitats. Total woody and seedling richness were similar between habitats at one site, but were richer under closed canopy at the other site. Sapling richness was higher in gaps at both sites and was a function of stem density at one site, but not at the other site.ConclusionsGaps are not always areas of higher woody species richness and therefore may be less important than expected for the overall species richness of woody plants. Instead, they are potentially important for enhancing local tree richness by increasing sapling richness. Gap disturbance is the primary driver of structural heterogeneity in forests where topographic and edaphic gradients are negligible.
Highlights
Forest canopy gaps differ from closed canopy or shaded understorey in terms of space, resources and, probably most importantly, light availability (Denslow 1987; Canham et al 1990)
The species composition of total woody species and seedlings was similar in both habitats, but species composition of saplings differed between habitats
Gap partitioning as a mechanism for species co-existence in the gaps is a rather weak explanation, considering total woody species and seedling richness in our study
Summary
Forest canopy gaps differ from closed canopy or shaded understorey in terms of space, resources and, probably most importantly, light availability (Denslow 1987; Canham et al 1990). Death and removal of dominant individuals change the competitive hierarchy among the species in a forest, and different species will be favoured for growth in open areas compared to areas under a closed canopy. Gaps and closed canopy areas are expected to support germination and growth of different suites of species, resulting in different composition and richness between them (Denslow 1987; Swaine & Whitmore 1988; Vilhar et al 2015). Gaps can create higher richness compared to closedcanopy forests at different scales. Gap partitioning sensu niche partitioning – a phenomenon by which species spatially partition space and resources in forest gaps from the gap centre to the edge
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