Dee Galt

Grazing Impacts on Rangeland Vegetation: What We Have Learned

Livestock grazing at light-to-moderate intensities can have positive impacts on rangeland vegetation in arid-to-semiarid areas. DOI:10.2458/azu_rangelands_v28i1_holechek

Long-term impacts of livestock grazing on Chihuahuan Desert rangelands.

Rangeland ecological condition was monitored over a 48 year period on 41 sites on Bureau of Land Management rangelands scattered across 6 counties in southwestern New Mexico. All sites were grazed by livestock during the study period. Sampling occurred in 1952, 1962, 1982, 1992, 1997, 1998, and 1999. A modified Parker 3 step method in conjunction with Dyksterhuis quantitative climax procedures were used to determine rangeland ecological condition. At the end of the 48 year study period (1952-1999), the average rangeland ecological condition score across study sites was the same (P > 0.05) as the beginning of the study (39% versus 41 % remaining climax vegetation, respectively). Major changes (P > 0.05) in rangeland condition occurred within the study period due to annual fluctuations in precipitation. Ecological condition scores increased in the 1980s and early 1990s due to above average precipitation. However, drought in the early to mid 1950s and again in the mid to late 1990s caused rangeland condition scores to decline. At the end of the study (1997-1999), 38% of the sites were in late seral ecological condition, compared to an average of 25% in the 1952 to 1982 period. The amount of rangeland in late seral ecological condition increased while the amount of rangeland in mid seral and early seral condition decreased in the 1990s compared to the 1952-1962 period. The average percent cover of black grama (Bouteloua eriopoda Torr.) and tobosa (Hilaria mutica Buckley), the primary forage grasses in the Chihuahuan Desert, were the same (P > 0.05) in 1952 and 1999. Over the 48 year study period, the average cover of shrubs including honey mesquite (Prosopis glandulosa Torr.) showed no change (P > 0.05). However major increases in honey mesquite basal cover occurred on 1 site and creosotebush (Larria tridentata [Pursh] Nutt.) increased on another. Grazing intensity was evaluated during the last 3 years of study (1997, 1998, 1999). Overall grazing use of forage across sites and years averaged 34% or conservative. Our research shows controlled livestock grazing is sustainable on Chihuahuan Desert rangelands receiving from 26-35 cm annual precipitation.

Grazing and Grazing Exclusion Effects on New Mexico Shortgrass Prairie

Abstract 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

Abstract 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.

A New Approach to Grazing Management: Using Multi-Herd/Variable Stocking

uring the past five years we have had the opportunity to develop and evaluate a new system of grazing management on two different ranches in New Mexico. We have named this grazing system multi-herd/variable stocking. The system we developed incorporates the knowledge gained from stocking rate and grazing system studies in the southwestern United States over the past 50 years. Variable grazing intensity levels, multiple herds of livestock, and deferment or rest of pastures with low forage production were integrated into a unified system. At any point in time the goal is to have cattle on 75% of the land while the remaining 25% of the area receives deferment or rest. Vegetation type was also considered in developing the plan. Upland pastures with a high component of palatable shrubs are targeted for winter use, while lowland pastures dominated by forbs or cool season grasses are reserved for spring use. After forage production has been determined in November, cattle are shifted away from pastures with the heaviest use and/or lowest forage production to grazing units with the opposite conditions. The goal is to lightly or conservatively graze weak pastures with low forage production while strong pastures with high forage production are targeted for moderate use. We will provide background information on how our multi-herd/variable stocking grazing plan was derived. Then we will discuss our approach to monitoring, drought planning, and preliminary results from the application of multi-herd/variable stocking on two ranches.

More On Stubble Height Guidelines

Factors to consider for shortgrasses and when making the decision if destocking is necessary. DOI:10.2458/azu_rangelands_v26i4_holechek