• Grazing and Grazing Exclusion Effects on New Mexico Shortgrass Prairie

      Holecheck, Jerry L.; Galt, Dee; Khumalo, Godfrey (Society for Range Management, 2006-11-01)
      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.
    • Long-Term Vegetation Trends on Grazed and Ungrazed Chihuahuan Desert Rangelands

      Molinar, Francisco; Navarro, Joe; Holechek, Jerry; Galt, Dee; Thomas, Milt (Society for Range Management, 2011-01-01)
      Long-term information on the effects of managed grazing versus excluded grazing effects on vegetation composition of desert rangelands is limited. Our study objectives were to evaluate changes in frequency of vegetation components and ecological condition scores under managed livestock grazing and excluded livestock grazing over a 38-yr period at various locations in the Chihuahuan Desert of southwestern New Mexico. Sampling occurred in 1962, 1981, 1992, 1998, 1999, and 2000. Range sites of loamy (1), gravelly (2), sandy (2), and shallow sandy (2) soils were used as replications. Black grama (Bouteloua eriopoda Torr.) was the primary vegetation component at the seven locations. Dyksterhuis quantitative climax procedures were used to determine trends in plant frequency based on a 1.91-cm loop and rangeland ecological condition scores. Frequency measures of total perennial grass, black grama, tobosa (Hilaria mutica Buckley), total shrubs, honey mesquite (Prosopis glandulosa Torr.), and other vegetation components were similar on both grazed and ungrazed treatments (P > 0.1) at the beginning and end of the study. The amount of change in rangeland ecological condition scores was the same positive increase (14%) for both grazed and ungrazed treatments. Major changes (P<0.1) occurred within this 38-yr study period in ecological condition scores and frequency of total perennial grasses and black grama in response to annual fluctuations in precipitation. Based on this research, managed livestock grazing and excluded livestock grazing had the same long-term effects on change in plant frequency and rangeland ecological condition; thus, it appears that managed livestock grazing is sustainable on Chihuahuan desert rangelands receiving over 25 cm annual precipitation. 
    • Moderate and light cattle grazing effects on Chihuahuan Desert rangelands

      Holecheck, Jerry; Galt, Dee; Joseph, Jamus; Navarro, Joseph; Kumalo, Godfrey; Molinar, Francisco; Thomas, Milt (Society for Range Management, 2003-03-01)
      Vegetation changes were evaluated over a 13 year period (1988-2000) on moderately grazed and lightly grazed rangelands in the Chihuahuan Desert of south central New Mexico. During the study period, grazing use of primary forage species averaged 49 and 26% on moderately and lightly grazed rangelands, respectiely. Autumn total grass and black grama (Bouteloua eriopoda Torr.) standing crop were consistently higher on the lightly than moderately grazed rangeland throughout the study. Total grass standing crop declined on the moderately grazed rangeland when the last 3 years of study were compared to the first 3 years (10 versus 124 kg ha-1), but showed no change on the lightly grazed rangeland (320 versus 357 kg ha-1). Black grama, the primary perennial grass in the Chihuahuan Desert, increased in autumn standing crop on the lightly grazed rangeland, but decreased on the moderately grazed rangeland (97% decline) than on the lightly grazed rangeland (67% decline). Perennial grass survival following a 3-year period of below average precipitation was higher on the lightly grazed (51%) than the moderately grazed rangeland (11%). Severe grazing intensities on the moderately grazed rangeland during the dry period (1994-1996) appear to explain differences in grass survival between these 2 rangelands. Our study and several others show that light to conservative grazing intensities involving about 25-35% use of key forage species can promote improvement in rangeland ecological condition in the Chihuahuan Desert, even when accompanied by drought.