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Species Abundance Distributions (SADs) for local tree communities in 1-ha forest plots on 20 tropical islands in the Indo-Pacific region

Citation

Ibanez, Thomas (2020), Species Abundance Distributions (SADs) for local tree communities in 1-ha forest plots on 20 tropical islands in the Indo-Pacific region, Dryad, Dataset, https://doi.org/10.5061/dryad.brv15dv7h

Abstract

Species abundance distributions (SADs) characterise the distribution of individuals among species. This dataset was used to investigate the relative importance of disturbance regime (tropical cyclone regime) and island geography (the area and isolation of islands) on the shape of SADs.

Methods

Tree species abundance data (i.e., the number of individuals for each tree species within a community), was obtained for 51 1-ha plots in humid tropical forests on 20 islands (13 archipelagos) in the Indo-Pacific region. Only plots without any evidence of recent natural or anthropogenic disturbances were conisidred (e.g., secondary forest plots, as defined by the author of source data, were removed). In each plot, all trees with a stem diameter 10 cm at c. 1.3 m above the base (DBH, diameter at breast height) were identified. All plots were located in lowland forests on islands larger than 1 km2. For each plot the number of trees (N), the number of tree species (R), and the shape parameter α of the gambin model (which characterize the shape of species abundance distributions, SADs) were computed. Standaridized R (Rstand)  and α (αstand) were also computed by randomly subsampling 400 trees per plot before counting the number of species and fitting gambin models. This process was repeated 100 times for each plot before estimating Rstand and αstand as the mean value of Ri and αi from all iterations. Island area (Area) and isolation (Dist) were extracted from the Island Directory (http://islands.unep.ch), mean annual temperature (MAT) and mean annual precipitation (MAP) were extracted for each plot location from CHELSA (http://chelsa-climate.org/) and a power dissipation index (PDI), a proxy of the energy released by cyclones, was computed using  the IBTrACs database (https://www.ncdc.noaa.gov/ibtracs/, see Knapp, Kruk, Levinson).

Funding

Hermon Slade Foundation, Award: HSF 19105

National Park Service, Award: P17AC00835