Community assembly explains invasion differences between two contrasting forest types

Plant communities within a metacommunity can vary widely in their degree of invasion by introduced species. Disturbance, propagule pressure, and biotic resistance are common explanations for this variation, but empirical evidence for these hypotheses is mixed.
Alternatively, the community assembly framework predicts that local assembly filters determine both native and exotic composition, but lower trait variation in the introduced species pool may exclude them from certain sites.
We examined evidence for this framework using observational data from forests and woodlands of Long Island, NY, USA. These forests vary in vegetation composition and invasion along a soil gradient. They are also highly disturbed and fragmented, yet some stands have almost no introduced plants.
Using data collected in 1998 and 2021-22, we quantified relationships between community composition, soil characteristics, and functional traits for native and exotic assemblages, as indicators of environmental filtering..., Study sites ­­
Community composition data used in this study was collected at two time points: 1998 and 2021-22. The 1998 data was gathered by Howard et al. (2004), who measured the vegetation composition and soil characteristics of 38 sites in Suffolk County, New York State, USA. The authors of the present study resampled 16 of these sites between 2021 and 2022.
Suffolk County is located on Long Island, east of New York City, and spans a land area of ~2300 km2. It has a hot-summer humid continental climate (Dfa) (Beck et al., 2018). The soils of the study area are generally acidic and well-drained to excessively well-drained (USDA-SSA & CAES, 1975). All study sites were located in protected forest preserves, except for a few that were on the campus of Brookhaven National Laboratory. These stands are open to the public and consist of fragmented secondary forests with various land-use histories.
Pine barrens communities had partially-open canopies of Pinus rigida and Quercus tree spe..., , # Community assembly explains invasion differences between two contrasting forest types

## Description of the data and file structure

#### Vegetation Composition Data

**1998_AboveDat.csv** - Vegetation composition data from the canopy of each field site, from the 1998 field surveys. This data was collected along a 30m transect in each site, with canopy cover of each species being estimated visually every 10 cm (see methods for details).  Column names: Site - name of site (see **sites.csv** for details), all other columns are abbreviated species names (see **Species_list.csv**), with the data in these columns representing the cover of each species in each site (max possible value = 3000).

**1998_belowDat.csv** - Vegetation composition data from the ground layer of each field site, from the 1998 field surveys. This data was collected along a 30m transect in each site, with the cover of each species being estimated in 10 cm segments using the line-intercept method (see methods for deta..., ,