Grazing and Grazing Exclusion Effects on New Mexico Shortgrass Prairie

Vegetative differences and changes were evaluated over a 6-year period (1999-2004) on adjoining conservatively grazed and grazing-excluded (22 years) shortgrass rangelands in northwestern New Mexico. Autumn total perennial grass and blue grama (Bouteloua gracilis [Willd. ex Kunth] Lag. Griffiths) standing crop did not differ on grazed and grazing-excluded areas when data were averaged across years. There were no long-term differences in vegetation basal cover or composition between the grazed and grazing-excluded areas. Plant community similarity values between the grazed and grazing-excluded areas were 80% and 93% during the first 2 years (1999-2000) and last 2 years (2003-2004) of study, respectively. Climatic conditions had more impact on vegetation composition of the 2 areas than livestock grazing. Similarity values between 1999-2000 and 2003-2004 periods were 52% and 64% for the grazed and grazing-excluded plant communities, respectively. At the beginning of our study, blue grama productivity was depressed on the grazed area compared to the exclosure, but after 3 years of conservative winter grazing, it was similar on the 2 areas. Our study indicates there is no benefit to blue grama rangelands from long-term rest from the standpoint of vegetation composition.