Each row in the "Simkin_et_al_2016_data_from_PNAS_Div_and_N_dep.csv" dataset represents one of 15,136 sites, and each of the 16 columns is a separate variable. The "README.csv" file contains descriptions corresponding to the 16 column header names, including the site coordinates (latitude and longitude), the response variable (species richness), the environmental variables (niitrogen deposition, precipitation, temperature, and pH), the output variables (critical loads of nitrogen with 95% confidence interval, as well as corresponding exceedance values), and assorted vegetation classification and data source variables. The "README.csv" also has further details about the multiple vegetation data sources corresponding to the abbreviated values in the "proj_orig" variable. The description of vegetation data sources is a text file adaptation of Table S1 in the Supplemental Material of Simkin et al. 2016 in the PNAS paper.