Long-Term Vegetation Productivity and Trend Under Two Stocking Levels on Chihuahuan Desert Rangeland

Abstract

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...

Effects of Different Improvement Treatments on Botanical Composition and Sediment Movement on Grazed and Enclosed Range Sites

“…Legume ratio and sediment yield were the highest in the year 2008, the lowest in the year 2006. The highest other families ratio was in the year 2008 and there was no significant difference between the years 2006, 2007).…”

Growth characteristics, reproductive performance, and evaluation of their associative relationships in Brangus cattle managed in a Chihuahuan Desert production system1

“…Excessive rainfall or drought in the Chihuahuan Desert can influence forage production for several consecutive years; thus, decreased animal growth rates in drought years were expected and observed in association with reduced forage quantity and quality. These years were identified, and the reports of Winder et al (2000), Beck et al (2007), (Khumalo et al (2007), and Thomas et al (2007a) describe the relationships between rainfall dynamics, forage production, and cattle performance in the Chihuahuan Desert. Trends across years in growth traits in these Brangus cattle were minimal relative to a multibreed producermanaged bull test facility in Tucumcari, NM (Garcia et al, 2004;Decker et al, 2008); however, data used in the current study were collected each year from all animals within this Chihuahuan Desert experiment station herd, whereas data collected from this public bull test facility were compiled each year from a few selected bull calves from numerous seed stock herds in New Mexico and surrounding states.…”

“…A noteworthy observation was the somewhat cyclic nature of the pregnancy percentage data underlying the quadratic response curve. This was most likely due to the influence of rainfall on forage production and subsequent animal performance in the Chihuahuan Desert, where an extremely high or low amount of precipitation in a specific year can influence range conditions for several subsequent years (Winder et al, 2000;Beck et al, 2007;Khumalo et al, 2007;Thomas et al, 2007a).…”

“…These supplements and feeding strategies were initially described by Obeidat et al (2002), and the supplements were purchased each year from local companies willing to provide competitive price bids for the feeds. Annual precipitation from 1972 to 2006 was 265 ± 13 mm, and stocking rate was 0.03 ± 0.01 animal unit/ha, which was a target forage use amount of ≤30% unless grazing experimentation required heavier use (Winder et al, 1992(Winder et al, , 2000Beck et al, 2007;Khumalo et al, 2007;Thomas et al, 2007a). Forage composition and fecal nutrient composition for these native rangelands were described by De Alba Becerra et al (1998), Obeidat et al (2002), and Bailey et al (2010).…”

“…After this procedure, they were again returned to the CDRRC for grazing and naturalservice mating. Cows were used in various grazing studies throughout their lives (Winder et al, 1992(Winder et al, , 2000Beck et al, 2007;Khumalo et al, 2007;Thomas et al, 2007a). Body weight and BCS data (range: 1 = emaci-ated, and 9 = obese) were collected each autumn at weaning and the weaning percentage was determined.…”