Plant community data from Rocky Mountain Biological Laboratory (CO, USA) transplant experiment 2017-2023

Description

Methods

We conducted this experiment at three sites in Washington Gulch near the Rocky Mountain Biological Laboratory (RMBL, Gothic, Colorado, USA) from June to September 2017-2023. We do not have data from 2020, as the Covid-19 pandemic prohibited travel and fieldwork. RMBL is located in the East River valley of the West Elk mountains, approximately 10 kilometers from Crested Butte, Colorado. Study sites were located at 2900 m (Low, 38.93248°N, -107.01018°W), 3150 m (Mid, 38.96046°N, -107.03262°W), and 3300 m (High, 38.97274°N, -107.04908°W) in elevation. The Low and Mid sites are in the montane vegetation zone, while the High is subalpine (Ackerfield, 2015). From the High to Low site, there is an increase in the growing season length, a mean growing season daytime air temperature difference of 1.9°C (2019 data from TOMST TMS-4 loggers placed at each site, Wild et al., 2019), and a mean growing season gravimetric water content difference of 0.17 g H2O per g dry soil. Fences were built around the sites to exclude cattle grazing. 

In the fall of 2017, we transplanted turfs within and between each of the three sites. We focused on grassland (grass/forb) vegetation and excluded shrubs when selecting turf locations. Each plot was 0.5 m x 0.5 m square and was moved intact to contain the entire plant community and an average of 20 cm of intact soil. To ensure replication, we divided sites into five blocks of five turfs each, arranged perpendicularly to the hillslope. In each block, we randomly assigned one of each treatment to each plot position (5 replicate turfs per treatment, 25 turfs total per site; Fig. 1). Treatments included: two ‘untouched controls’, a disturbance control that was locally transplanted, a one- or two-step warmer transplant (W1 and W2), and a one- or two-step cooler transplant (C1 and C2). “One-step” indicates that the turf was transplanted one site higher or lower, whereas “two-step” indicates the turf was transplanted two sites higher or lower. When transplanting, we maintained the orientation of each plot relative to the hillslope. Immediately after transplantation, we watered turfs from local streams and covered them with shade-cloth canopy for one month. In anticipation of natural disturbance from gophers, we added a sixth block of transplanted turfs (5 at the High site, 4 at the Mid site, and 6 at the Low site) in 2018, bringing the total to 90 turfs.

We installed nets around each turf (1 m x 1 m) in the growing season months to prevent gene flow from the transplanted plants to the surrounding plant communities. To preserve species interactions despite the nets, we centered each 0.25-square meter plot in a 1 m2 net, providing a buffer of destination site vegetation under the net. One untouched control was left un-netted in each block to test for the effect of nets. 

In 2017 only, before transplantation, we collected baseline plant species abundance data by counting individuals of each species in one turf (out of five) in each of the five blocks per site at time of peak plant biomass. From 2018-2023 (excluding 2020), we collected species percent cover data on all turfs for all species at the time of peak biomass in mid-late summer. We estimated the percent cover of each species in the plot to the nearest 1% using a 50 cm x 50 cm frame with a grid of 10 cm x 10 cm subturfs. We also recorded species presence/absence in each subplot.