Seasonal and yearlong Grazing in the Northern Chihuahuan Desert: Impacts on Forage and Cow?Calf Production
three-pasture seasonal suitability grazing system was studied from 1967 to 2002 ... Chihuahuan Desert Rangeland Research Center (CDRRC)
One herd of cows was rotated through three pastures each year. Another herd of cows grazed continuously yearlong in a fourth pasture.
varied from grassland dominated by black grama (Bouteloua eriopoda[Torr.] Torr.) and mesa dropseed (Sporobolous fleuosus [Thurb. Ex Vasey] Rydb.) to dense mesquite (Prosopis glandulosa Torr.). Total annual production of the common perennial grasses averaged 150 lb./acre across the pastures, ranging from 3 lb./acre in the driest year (2002) to nearly 420 lb./acre in the wettest year (1986). Annual plants produced an average of 71 lb./acre during the study. Annual plant produc-tion was greater than 490 lb./acre at the start of the study but declined to zero production in drought years
Average perennial grass utilization ranged from 16% to 26% with an average near 21% on both grazing systems.
In drought years, utiliza-tion sometimes exceeded 50% on some perennial grass species
Calf weaning weights at an average of 7 months of age averaged 477 lb. on the sea-sonal pastures and 494 lb. on the yearlong pasture.
Both herds of cattle were removed from the pastures from late 1994 to early 1997 because of drought conditions
No long-term differ-ences were detected for calf production or changes in vegetative composition between the two grazing management systems.
Amount of rain, frequency of rain events, and the season in which it fell appeared to be most critical in determining plant composition changes across the pastures.
The number of forage plants is declining because of increasing populations of mesquite, broom snake-weed (Gutierrezia sarothrae[Pursh] Skinners) and other invasive plants.
any livestock grazing will need to be flexible by adjusting stocking rates and season of grazing
deteriorated stage because of overgrazing and drought (Valentine 1970)
Grasses once dominated most of these lands, ac-cording to reports written in the 1800s by explor-ers and settlers (Gibbens et al. 2005). Black grama (Bouteloua eriopoda[Torr.] Torr.) was recognized as the most important forage grass on the up-lands (fig. 1; Gardner 1951, Nelson 1934).
Black grama has moderate palatability and only becomes important forage when other grasses and forbs are dry. Droughts in the 1930s and the 1950s caused serious reduction of black grama stands (Paulsen and Ares 1962). Black grama was also seriously af-fected by drought in the early 1970s again by drought that started in the 1990s
Herbel and Gibbens (1996) reported that black grama recovered very little from the drought of the 1950s on deeper sandy soils on the USDA Jornada Experimental Range, which is located just east of the Chihuahuan Desert Range-land Research Center. The greatest recovery from drought was on shallow soils. Two characteristics of black grama make restoration a difficult, slow process: (1) very low production of viable seed; and (2) dependence upon vegetative reproduction by stolons and rooting buds that are susceptible to damage by grazing, trampling, and drought (Valen-tine 1970).
Dropseeds (Sporobolusspp.) and threeawns (Aristida spp.) are often considered to be secondary forage and provide less soil protection (Paulsen and Ares 1962)
However, deteriorated rangelands may never recover their former productivity because of overgrazing and drought, especially on deep soils (Herbel et al. 1974).
Seeding of grass and forb species is a pos-sibility on many ranges, but is not practical on arid rangelands found in southern New Mexico because of cost and possible erosion hazard from disturb-ing the soil for seedbed preparation (Holechek et al. 1998). [yeoman's/swaling is an erosion hazard?]
On rangelands not dominated by mesquite that are in poor-to-fair range condition, it is recom-mended that either stocking be reduced or some type of grazing system be developed that will op-timize either the maintenance or establishment of new perennial forage plants (Beck 1980)
drought that started in 1994 provided the opportunity to observe the impact of drought on desert rangelands with and without cattle grazing.
study pastures were located at the Chihuahuan Desert Rangeland Research Center (CDRRC), 24 miles north of Las Cruces, New Mexico The terrain of the pastures is nearly level, with slopes less than 2%. Average elevation of the pastures is near 4,350 ft. above sea level
average annual precipitation for the area is 9.3 in. (1931-2002). Because of several years of above-average rainfall from the late 1970s to the early 1990s, average long-term annual rainfall increased from 8.5 in. to 9.3 in. by 1992
sum-mer growing season precipitation, May through September, changed from 5.6 in. to 5.8 in. (62% of the annual total) in the same period. Another small peak of precipitation occurs from December through January with some precipitation falling as snow.
Average daily maximum temperatures vary from a high of 97º F in June to 55º F in January
Figure 5. Summer (May through September) and annual (January through December, total bar height) precipitation for 1967 to 2002 [pdf 4]
temperature fluctuations of 35º F or more between morning lows and afternoon highs occur frequently throughout the year except in the summer rainy season, when daily fluctuations of 15º F to 20º F are more common
most common perennial grasses are black grama, dropseeds, and threeawns. In most years, threeawns are the first grasses to start growth in the spring and early summer, followed by drop-seeds, with black grama starting growth in warmer temperatures.
Mesa dropseed (Sporobolus flexuosus[Thurb. Ex Vassey] Rydb) was the most common, spike dropseed (S. contractusA. S. Hithchc.) was the second most common, and some sand dropseed (S. cryptan-drus[Torrey] Gray) was also present.
most common species were purple threeawn (Aristida purpurea Nutt.), Wooton?s threeawn (A. pansaWoot. & Standl.) and Havard threeawn (A. havardiiVasey). The most common shrub is mesquite. Broom snakeweed (Gutierrezia sarothrae[Pursh] Skinners) is also common in some areas. Many other plant species including forbs such as leatherweed croton (Croton potsii[Klotzsch] Muell.-Arg.), spectacle-pod (Dimorphocarpa wislizenii[Engelm.] Rollins), and paperflower (Psilostrophe tagetina[Nutt.] Rydb.) can occur in abundance in years of average to above average rainfall.
Soils on the pastures are mainly Petroargids and vary from loamy fine sands to sandy fine loams and generally have depths of 20 in. or less to a caliche layer (Teaschner 2001).
yucca (Yucca elataEngelm.) and longleaf ephedra (Ephedra trifurcaTorrey)
When annual grasses and forbs produced abun-dant growth due to local rain-showers in the pas-tures not being grazed, the cattle were sometimes moved into these pastures for a few days to utilize the green forage, and then were moved back to the original pasture to complete the grazing sea-son.
For the first few years of the study, water was pumped by windmills (fig. 10) into storage tanks and then gravity fed through pipelines to drinking tanks (fig. 11). Often during the sum-mers there was inadequate wind to pump enough water
Figure 12. The cows frequently grazed in the low areas or depres-sions that characterize the landscape across the study pastures. During extended dry periods, these depressions often grew the only green forage available in the pastures. Many of the depres-sions also had dense stands of mesquite compared with the more open savannah on the surrounding uplands. [low areas, like swales?]
Figure 13. Total perennial grass production on the yearlong pasture and seasonal pastures from 1967 to 2002 [pdf 8][lbs/acre, use this data]
Summer growing season precipitation varied from over 11.1 in. in 1986 to less than 2.4 in. in 1994
Annual precipitation varied from nearly 5.2 in. in 1970 to about 18.4 in. in 1986.
In most years the majority of the perennial grass growth occurs from July through September when about 50% of the annual rainfall occurs.
Many annual grasses and forbs grew during the summer rainy season, but year-to-year abundance of these annuals was not predictable as they depend on amount of precipitation and frequency of events
In some years winter-spring annual forbs grow in the pastures, but they generally have low palatability and provide little to the total diets (Mofarreh et al. 1997).
The presence of cool season annuals varies widely from year-to-year. Their pres-ence and abundance is dependent upon fall and ear-ly-winter precipitation [and temp]
The reasons for the high annual plant production in 1968 and 1974 are not clear. Both years had very low precipitation during the preceding dormant months followed by average to above-average sum-mer rains. During the early years of the study, large populations of Russian thistle (Salasola tragus L.) grew on the pastures and may have accounted for part of the high annual production for those years.
these three perennial grass-es compose more than 80% of the forage
The amount of forage produced during the summer depended on how quickly the grasses responded to any rain
In dry years with limited forage, such as 1994, utiliza-tion averaged more than 37%. In high rainfall years such as 1978, with large amounts of forage avail-able, utilization was near 10% on the pastures. In years of higher rainfall, the cows were not limited to perennial grasses but ate a large variety of plants (Mofareh et al. 1997)
Overall average grazing use of perennial grasses was higher (P=0.10) on the winter-spring pasture than on the other two pastures because there were fewer forage choices in that season
threeawns were eaten more (P=0.10) in the winter-spring pasture [only things available w/ leaf]
Dropseeds were important forage plants during the growing season but were not important in cattle diets in the dormant season (Mofareh et al. 1997).
Black grama was grazed year-round but was utilized more (P=0.10) in the fall pasture when other plants began to senese and become dormant.
In the yearlong pasture the cows grazed the dif-ferent vegetation types in different seasons.
pe-rennial forbs such as leatherweed croton and pale scarlet globemallow (Sphaeralcea angustifolia[Cav.] D. Don).
Changes in perennial grass basal cover were similar across all four pastures. Season of grazing appeared to have little influence on any changes measured; rather changes were in response to years of either abundant rain or drought
Production of major plant species, weaning weights and weaning percentages were generally similar between the seasonal-suitability and yearlong graz-ing systems for the 36 years that data were col-lected.
[light stocking, heavier could give different responses.light to contend with dry seasons w/o having to take all the cows off the land]
Stocking below carrying capacity has been recognized since the early 1900s as an important management op-tion in the arid Southwest (Sampson 1923)
grazing generally had only a minor impact on any herbaceous vegeta-tion changes. The amount of rainfall and the season in which it fell were more critical factors causing plant composition changes. Gibbens and Beck (1988) made similar conclusions after evaluating 64 years of quadrat data from the Jornada Experimen-tal Range. They reported that compared to fluc-tuations in annual precipitation grazing had little impact on perennial grass cover
2. The surface of the soil actually covered by a plant, as compared to the full spread of the herbage, which in grassland ecology often measures at one inch above the ground.
Teaschner (2001) reported on changes in mes-quite density from 1982 to 2000 in relation to soil depth across the study pastures. Average mesquite density increased from 55 to 138 plants/acre on soils less than 20 in. deep, from 60 to 192 plants/acre on soils 20 to 40 in. deep, and from 79 to 217 plants/acre on soils greater than 40 in. deep. Even from 1993 to 2000, which included many dry years, mesquite density increased 11% or more on all soils.
In 1982, some of the grasslands had no mesquite present, but by the year 2000, no area in the pastures was completely free of mesquite
By 2000, average mesquite canopy cover was 5% or greater across the pastures with some areas having 25% or more mesquite canopy cover [Teaschner (2001)]
Opportunities to improve or restore these for-mer grasslands are limited by the low amount of precipitation. Improvement practices used in more mesic rangelands such as seeding are generally not practical in a desert environment because of low returns on investment and potential soil loss from any mechanical disturbance. Use of herbicides to control shrubs is an important alternative because herbicides are selective against woody vegetation and do not affect herbaceous plants or disturb the soil.
livestock grazing needs to be flexible, including periodic adjustment of stocking rates and season of grazing.