This project was designed to examine the long-term response of semi-arid vegetation communities to the removal of dominant species. One dominant species representing each of the three major biomes occurring at the Sevilleta National Wildlife Refuge was selected for removal from the sampled plots. These species included: Bouteloua gracilis (blue grama), the characteristic dominant grass of shortgrass steppe, Bouteloua eriopoda (black grama), a dominant grass of Chihuahuan Desert grassland, and Larrea tridentata (creosotebush), a dominant shrub of Chihuahuan Desert shrubland.
The study began in 1995, when all plants of the dominant species were removed from five 3 m x 4 m plots within patches dominated by B. gracilis, B. eriopoda, or L. tridentata. Further, plots in which dominant species were removed were established in transition communities dominated by either B. gracilis and B. eriopoda or B. eriopoda and L. tridentata. Five control plots without removals were also established. An additional set of plots was added in 1998 near the foothills of the Los Pinos Mountains. These plots burned during the lightning-ignited Bootleg Fire of June 1999.
Plots are maintained by periodic removal of regenerating dominant species. All plots are sampled in September, near the end of the growing season, for vegetative cover by species. Erosion bridges are being used in a subset of plots to monitor soil redistribution. Vegetation data is also being related to data collected on seed production and seed presence within the patches and is being utilized for the validation of simulation models.
Key findings after the first five years of data collection are that removal of B. gracilis or L. tridentata results in an increase in perennial forbs whereas removal of B. eriopoda results in an increase in perennial grasses. Patterns in the cover of annuals are similar for all plot types and are largely related to weather in the year of sampling.