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The thermal niche and phylogenetic assembly of evergreen tree metacommunities in a mid-to-upper tropical montane zone

Citation

Das, Arundhati; Ratnam, Jayashree (2022), The thermal niche and phylogenetic assembly of evergreen tree metacommunities in a mid-to-upper tropical montane zone, Dryad, Dataset, https://doi.org/10.5061/dryad.70rxwdc14

Abstract

Frost and freezing temperatures have posed an obstacle to tropical woody evergreen plants over evolutionary timescales. Thus, along tropical elevation gradients, frost may influence woody plant community structure by filtering out lowland tropical clades, and allowing extra-tropical lineages to establish at higher elevations.

Here we assess the extent to which frost influences the taxonomic and phylogenetic structure of naturally-patchy evergreen forests (locally known as shola) along a mid-upper montane elevation gradient in the Western Ghats, India. Specifically, we examine the role of large-scale macroclimate and factors affecting local microclimates, including shola patch size and distance from shola edge, in driving shola metacommunity structure. We find that the shola metacommunity shows phylogenetic overdispersion with elevation, with greater representation of extra-tropical lineages above 2000m, and marked turnover in taxonomic composition of shola woody communities near the frost-affected forest edge above 2000m, from those below 2000m. Both minimum winter temperature and patch size were equally important in determining metacommunity structure, with plots inside very large sholas dominated by older tropical lineages, with many endemics. Phylogenetic overdispersion in the upper montane shola metacommunity thus resulted from tropical lineages persisting in the interiors of large closed frost-free sholas, where their regeneration niche has been preserved over time.

Methods

A stratified random sampling design was used to collect shola woody vegetation data from 20 x 20 m plots, based on slope, aspect, and landscape context. A minimum of four plots were placed within each combination of landscape context and topographic class, with the exact location of plots determined by accessibility and steepness of terrain. In large shola patches (> 60 ha), three transects of plots were placed at a minimum of 250 m apart, with a distance of at least 50 m between each plot along the transect. All non-climbing woody individuals > 1cm diameter were censused within the plots. In addition, the distance to the nearest edge of the shola fragment was noted as well as plot elevation. A total area of 3.48 ha (87 plots) was censused across 60km2 study area loacted in the southern and western part of the Upper Nilgiris plateau in south India (11.17oN, 76.77oE and 11.50oN and 76.43oE), between 1750-2400 m ASL.

The presence and abundance of each species in each plot was derived from this field dataset, as was distance to edge measurements and elevation. Size of the shola patch was calculated in QGIS software after digitizing each sampled shola patch using 2.5 m resolution QuickBird imagery in Google Earth (www.googleearth.com; Digital Globe Imagery from 2008-2011, accessed Aug 2011).

Usage Notes

The data files are in .csv format and can be opened in MS Excel and in the R statistical software.

Funding

Department of Biotechnology, Government of India