N and P addition experiment colonization data for Niwot Ridge from 2015 to 2019, yearly

In 2014 we established 20 experimental plots (25 x 25 cm) at four Snowbed Experiment sites (Arikaree, D1, Martinelli, and Soddie) in order to investigate the effect of nitrogen (N) and phosphorous (P) nutrient additions on plant colonization in snowbed areas with a recently diminishing persistence of summer snow cover. Plots were established in areas of persistent snow cover where there was only bare soil and no plants growing. Treatments included (1) control (no nutrient additions), (2) N addition, (3) P addition, and (4) N + P addition. At each site, plots were grouped into five blocks, with one of each of the four treatment plots present in each block (4 sites x 5 blocks x 4 treatments = 80 plots). Treatments were assigned randomly (without replacement) within blocks.