Factors Determining Forest Diversity and Biomass on a Tropical Volcano, Mt. Rinjani, Lombok, Indonesia

Gbadamassi G O Dossa,Rhett D Harrison,Junichi Fujinuma,Sherryl Paz,Ekananda Paudel,Wanlop Chutipong,Yuan Zhang,Haiying Yu,Nathan G Swenson

doi:10.1371/journal.pone.0067720

Abstract

Tropical volcanoes are an important but understudied ecosystem, and the relationships between plant species diversity and compositional change and elevation may differ from mountains created by uplift, because of their younger and more homogeneous soils. We sampled vegetation over an altitudinal gradient on Mt. Rinjani, Lombok, Indonesia. We modeled alpha- (plot) and beta- (among plot) diversity (Fisher's alpha), compositional change, and biomass against elevation and selected covariates. We also examined community phylogenetic structure across the elevational gradient. We recorded 902 trees and shrubs among 92 species, and 67 species of ground-cover plants. For understorey, subcanopy and canopy plants, an increase in elevation was associated with a decline in alpha-diversity, whereas data for ground-cover plants suggested a hump-shaped pattern. Elevation was consistently the most important factor in determining alpha-diversity for all components. The alpha-diversity of ground-cover vegetation was also negatively correlated with leaf area index, which suggests low light conditions in the understorey may limit diversity at lower elevations. Beta-diversity increased with elevation for ground-cover plants and declined at higher elevations for other components of the vegetation. However, statistical power was low and we could not resolve the relative importance to beta-diversity of different factors. Multivariate GLMs of variation in community composition among plots explained 67.05%, 27.63%, 18.24%, and 19.80% of the variation (deviance) for ground-cover, understorey, subcanopy and canopy plants, respectively, and demonstrated that elevation was a consistently important factor in determining community composition. Above-ground biomass showed no significant pattern with elevation and was also not significantly associated with alpha-diversity. At lower elevations communities had a random phylogenetic structure, but from 1600 m communities were phylogenetically clustered. This suggests a greater role of environmental filtering at higher elevations, and thus provides a possible explanation for the observed decline in diversity with elevation.

Highlights

Biotic communities are differentiated in space and time, and understanding this feature of biodiversity is fundamental to ecology [1]
Canopy height and subcanopy tree density were linearly correlated with elevation, while for canopy tree density (R2 = 0.33, F2, 15 = 5.23, P = 0.02), tree basal area (R2 = 0.42, F2, 15 = 7.07, P = 0.006), and leaf area index (LAI: R2 = 0.56, F2, 15 = 11.95, P,0.001) the data suggested a humped-shaped relationships and for canopy openness (R2 = 0.69, F2, 15 = 20.22, P,0.001) the data suggested a U-shaped relationship with elevation (Fig. 2)
Model averaging indicated that elevation was the only important factor in determining species diversity for understorey, subcanopy, and canopy plants, while elevation and LAI were both important for ground-cover vegetation (Table 1)

Summary

Introduction

Biotic communities are differentiated in space and time, and understanding this feature of biodiversity is fundamental to ecology [1]. The patterns and mechanisms of changes in species diversity and composition with altitude and latitude remain controversial [2]. It is widely accepted that patterns of change in species diversity with elevation are based on parallel changes in climate with elevation, and that altitudinal gradients of species diversity in humid regions often mirror the latitudinal pattern [3,4]. Biologists have studied patterns of species diversity and compositional change along altitudinal gradients for over a century [2,3,5–. Climatic variation, edaphic factors, and biotic factors might explain this changing pattern, but none of these is unambiguous. To what degree floristic composition is determined by environmental factors depends on other key ecosystem processes, such as dispersal limitation and biotic interactions, and is hotly debated [16,17,18]

Methods

Results

Conclusion