Consistent patterns of elevational change in tree taxonomic and phylogenetic diversity across Malesian mountain forests

Abstract

Aim In order to investigate the relative importance of ecological (habitat specialization) and biogeographical (speciation, geographical dispersal limitation) processes as causes of non‐random spatial distribution of tree species in the mountain forests of Malesia, we analysed the elevational change in the taxonomic and phylogenetic diversity of tree assemblages in different biogeographical subregions. Location Malesia (Borneo, Java, Sulawesi and the Philippines). Methods Tree inventory data of 12 old‐growth forests from a wide elevational range (650–3080 m a.s.l.) were taxonomically harmonized and standardized (50 random draws of 245 individuals each per plot), and the phylogeny of 204 genera was resolved and scaled to its evolutionary origin. The taxonomic and phylogenetic diversities were calculated using effective generic measures, and the diversity patterns analysed by regression, ordination and classification. Results The primary factor determining the diversity patterns of the tree assemblages was elevation, whereas the influence of region was surprisingly low. This results in common elevational patterns in taxonomic and phylogenetic community structure across western and central Malesia. The major clades of the contemporary mountain forest trees must therefore have evolved before the formation of the Malay Archipelago in its present form (sympatric speciation). Taxonomic richness and phylogenetic diversity exhibited opposite trends with elevation. Generic richness decreased linearly with elevation; the phylogenetic structure of high‐elevation forests revealed overdispersion, indicating convergent trait evolution towards higher elevations, whereas the submontane and colline assemblages showed clustering with a considerable number of confamilials. The upper montane forests of Borneo and Sulawesi were characterized by the dominance of Southern Hemisphere conifers, which differentiated them from lower‐elevation communities. Main conclusions Our results indicate that ecological, evolutionary and biogeographical processes (environmental filtering, sympatry and long‐distance dispersal) have shaped the contemporary community structure of Malesian mountain forests. Wallace's Line may represent a significant barrier between the lowland tree floras of Borneo and Sulawesi, but this is not true for those at higher elevations. The uniqueness of high‐elevation forests in terms of their high phylogenetic diversity and of their unusual structure calls for a high priority in conservation programmes.

Compound-specific carbon isotope records of vegetation and hydrologic change in central Sulawesi, Indonesia, since 53,000 yr BP

“…While Poaceae indicates increasing aridity, which in itself might have driven the enrichment of δ 13 C wax during the glacial period, Castanopsis and Lithocarpus might indicate that colder, higher-altitude tree taxa migrated to lower elevation areas closer to Lake Matano, presumably due to cooler LGM temperatures. Fagaceae, including Lithocarpus and Castanopsis, is highly abundant in the high mountains around Lake Matano, as has been observed in other mountain forests across Sulawesi (Culmsee et al, 2010;Culmsee and Leuschner, 2013). Interestingly, Fagaceae plants from settings comparable to our study site (i.e.…”

The Role of Environmental Filtering in Structuring Appalachian Tree Communities: Topographic Influences on Functional Diversity Are Mediated through Soil Characteristics

“…In particular, the development of phylogenetic and functional diversity indices has provided greater insight than traditional taxonomic-based measures, allowing quantification of community-level convergence (clustering) and divergence (overdispersion) of traits described by PTH and SDH. Using these newer diversity metrics, many studies of tropical forest communities have shown that trait convergence is more prevalent in stressful environments and that topography and soil fertility can act as strong selective forces during community assembly [12][13][14][15][16][17][18][19]. Similar studies have been conducted in temperate forests, but they are fewer and the results seem to show less consistent support for SDH and PTH [10,[20][21][22][23][24].…”

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

“…For example, it has been shown that patterns of community assembly along elevational gradients are non‐random (Cadotte et al, ; Qian & Ricklefs, ), and in particular, environmental filtering has been shown to play a key role in community assembly at high elevations where harsher environments occur (Qian, Hao, & Zhang, ; Xu et al, ). However, plants tend to be phylogenetically overdispersed at high elevations (Bryant et al, ; Culmsee & Leuschner, ), which could result from a number of mechanisms, such as the selection of convergent traits or facilitation among distantly related lineages, or ecological mechanisms like competition or disease sharing that can limit the coexistence of close relatives. As a result, community assembly rules along elevational gradients are complex and are not often represented by a shift in singular processes (e.g.…”