Perennial grass production on the Chihuahuan Desert Rangeland Research Center in south-central New Mexico was correlated with precipitation characteristics over a 34-year period. Total December through September precipitation was highly correlated (r ¼ þ0.77, n ¼ 34) with perennial grass production. Practical generalized indices were developed that could be broadly applied by managers for predicting perennial grass production from precipitation characteristics. Perennial grass production and precipitation data on 3 separate pastures were collected over a 6-year period to evaluate the reliability of models to predict perennial grass production. Simple linear, 2-variable, quadratic, and polynomial regression models gave perennial grass production estimates that were well correlated with actual values (r ¼ þ0.85 to þ0.91, n ¼ 17) across the 3 pastures. The quadratic regression model (Y ¼ 4.04 À 0.24X þ 0.012 X 2 , X ¼ December through September precipitation, Y ¼ forage production, n ¼ 34, r ¼ 0.85) gave the most accurate predicted values. Our quadratic regression model should be of practical use to ranchers and range managers on Chihuahuan Desert upland rangelands receiving 200-300 mm annual precipitation, with loamy to sandy loam soils and in mid-to late-seral ecological condition. These conditions match those generally found on Chihuahuan Desert Uplands. We consider our quadratic regression model to be highly useful over large areas to ranchers in southern New Mexico, southeastern Arizona, southwestern Texas, and north-central Mexico. Resumen La producció n de zacates perennes en el Centro de Investigació n de Pastizales del Desierto Chihuahuense en la regió n sur-central de New Mexico se correlacionó con las características de precipitació n de un periodo de 34 añ os. La precipitació n total de Septiembre a Diciembre estuvo altamente correlacionada (r ¼ þ0.77, n ¼ 34) con la producció n de zacates perennes. Se desarrollaron índices prá cticos generalizados que pudieran ser aplicados ampliamente por los manejadores para predecir la producció n de zacates perennes a partir de las características de precipitació n. Los datos de precipitació n y producció n delos zacates perennes de tres potreros separados se colectaron en un periodo de 6 añ os para evaluar la confiabilidad delos modelos para predecir la producció n de zacates perennes. Modelos de regresió n lineal simple, de dos variables cuadrá ticos y polinomiales dieron estimaciones de la producció n de zacates perennes que estuvieron bien correlacionados con los valores actuales (r ¼ þ0.85 a þ0.91, n ¼ 17) a través de los 3 potreros. El modelo cuadrático de regresió n (Y ¼ 4.04 À 0.24X þ 0.012 X 2 , X ¼ precipitació n de Septiembre a Diciembre, Y ¼ producció n de forraje, n ¼ 34, r ¼ 0.85) dio los valores de predicció n má s certeros. Nuestro modelo de regresió n cuadrá tica debe ser de uso practico para los rancheros y manejadores de pastizales de la parte alta del Desierto Chihuahuense que reciben una precipitació n anual de 200-300 mm y con suelos de textura...
Vegetation changes were evaluated over an 11-year period (1995-2005) on 2 light-and 2 conservative-stocked Chihuahuan Desert pastures in south central New Mexico. Grazing treatments were applied to the pastures over a 5-year period from 1997 through 2001. Pastures were not grazed in the 1995-1996 and 2002-2005 periods due to drought. During the 1997-2001 grazing period, grazing use of primary forage species averaged 29% and 40% on light-and conservative-stocked rangelands, respectively. Grazing intensity was consistently higher on conservative-stocked than light-stocked pastures. During our study heavy grazing occurred only in 1 year on pastures with conservative stocking. There were no differences in species or species categories (grasses, forbs, shrubs) of autumn standing crop and basal cover between light-and conservative-stocked pastures. Standing crop of total vegetation and perennial grasses showed large fluctuations among the years due to variable rainfall. Under both treatments, total herbaceous standing crop was unchanged, but perennial grass standing crop declined by over 50% when the last 3 years of study were compared with the first 3 years of study. Broom snakeweed (Gutierrezia sarothrae Pursh), a poisonous half shrub, increased in standing crop and cover during the study. Basal cover of total perennial grasses declined less under light than conservative stocking during the study period. However, climatic conditions exerted the overriding influence on vegetation standing crop and basal cover. Our study indicates that light stocking in the Chihuahuan Desert does not increase perennial grass production compared to conservative grazing but it could have a small benefit in maintaining perennial grass cover during drought. We believe our findings have broad application in the Chihauhuan Desert, but caution they might not apply well to other arid rangeland types. Resumen Se evaluaron los cambios de vegetació n por un periodo de 11 añ os (1995-2005) en dos poteros del Desierto Chihuahuense de la regió n sur-central de New Mexico con carga animal ligera y dos con una carga animal conservadora. Los tratamientos de apacentamiento fueron aplicados a los potreros por un periodo de cinco añ os de 1997 al 2001. Los poteros no se apacentaron en los periodos de 1995-1996 y 2002-2005 debido a la sequía. Durante el periodo de apacentamiento 1997-2001, la utilizació n de las principales especies forrajeras promedio 29% y 40% en los pastizales con cargas ligera y conservadora respectivamente. La intensidad de apacentamiento fue consistentemente mayor en los potreros con carga conservadora que en los de carga ligera. Durante nuestro estudio, solo en un añ o ocurrió apacentamiento fuerte en los potreros con carga conservadora. Entre cargas animal no hubo diferencias en la biomasa de otoñ o y la cobertura basal de las especies o categorías de especies (zacates, hierbas, y arbustos). La biomasa de la vegetació n total y de los zacates perennes presentó grandes fluctuaciones entre añ os, debido a la variabilidad de la precip...
Soil depth effects on honey mesquite (Prosopis glandulosa Torr) cover and density and perennial grass standing crop were evaluated over an 11-yr period (1995-2005) on two lightly stocked and two conservatively stocked pastures on the Chihuahuan Desert Rangeland Research Center in south-central New Mexico. These four adjoining pastures have similar size, vegetation, and soils. Soils in these study pastures are primarily light sandy loams varying from a few centimeters to 1 m or more in depth underlain by a calcium carbonate layer. Deep soils had lower perennial grass standing crop and higher honey mesquite cover and density than did shallow soils at both the beginning (1995-1997) and ending (2003-2005) periods of study. Average perennial grass standing crop across the four study pastures dropped 82% between 1995-1997 and 2003-2005 because of drought during the last 5 yr of study. Honey mesquite canopy cover and perennial grass standing crop did not differ between light and conservative grazing treatments at the beginning or end of our study. Honey mesquite canopy cover did not change
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. Resumen Las diferencias vegetativas y sus cambios se evaluaron por un periodo de seis añ os (1999-2004) en dos pastizales de zacates cortos adjuntos y ubicados en el noroeste de New Mexico, uno de ellos apacentado conservativamente y el otro excluido al apacentamiento (22 añ os). La biomasa total de zacates perennes y de ''Blue grama'' (Bouteloua gracilis [Willd. ex Kunth] Lag. Griffiths) en otoñ o, promediada a través de los añ os, no difirió entre las á reas apacentada y excluida. No hubo diferencias a largo plazo en términos de cobertura basal de la vegetació n o su composició n entre las dos á reas evaluadas. Los valores de similaridad de la comunidad vegetal entre las á reas apacentada y excluida fueron 80% y 93% durante los primeros dos añ os (1999-2000) y los dos ú ltimos (2003-2004) del estudio respectivamente. Las condiciones climá ticas tuvieron má s impacto sobre la composició n de la vegetació n de las dos áreas que el apacentamiento. Los valores de similaridad entre los periodos de 1999-2000 y 2003-2004 fueron 52% y 64% para las comunidades vegetales apacentada y excluida, respectivamente. Al inicio de nuestro estudio la productividad del ''Blue grama'' disminuyó en el á rea apacentada en comparació n con la excluida, pero después de tres añ os de apacentamiento conservativo en invierno fue similar en las dos á reas. Nuestro estudio indica que, desde el punto de vista de la composició n de la vegetació n, no hay beneficio para el ''Blue grama'' por el descanso de largo plazo.
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