Honey Mesquite Influences Chihuahuan Notes

• Our data show that under proper std&ing both mesquite and perennial forages grasses can increase concurrently on desert grassland ranges.


• Our data indicate mesquite den-sity and cover increase rapidly after herbicidal mesquite control even under conservative stocking.


• Research has shown mesquite control can increase forage production for 5 to 10 years post treatment (Herbel et al. 1983, Gibbens et al. 1986)


• Low and moder- ate honey mesquite areas are defined as having 9% and 16% canopy cover


• data collected in 1968, 1972, 19S2, and 1992


• New Mexico State University College Ranch located 40 km north of Las Cruces, Doiia Ana County, College Ranch lies in the southern portion of the Jomada de1 Muerto Plain between the San Andres Mountains and the Rio Grande River. The elevation of 1,340 m. Topography is generally level with all slopes less than 5%. The area is arid, with no permanent water except for the river and stock watering points supplied by wells and temporary earth- en tanks. Annual precipitation during the study period varied from 190 to 296 mm, with a 30-year (1961 to 1990) average of 248 mm.


• Half rainfall between July and September


• -23? to 42°C and extreme daily fluctuations of 30°C. June is the warmest month and January the coldest


• n stocked for an average uti-lization level of about 30% on the key forage species. During the 1986-1990 period the actual stocking range has averaged 48 ha per animal unit.


• atment between 1957 and 1964 with either 2,4,5-T, Fenuron or Monuron (McNeely 19S3, Tembo 1990). Percent actual kill of mesquite (tops and roots) ranged from 65 to 93%. These treat-ments are discussed in detail by McNeely (1983


• Correlation coefficients for mesquite density, height, maximum diameter, minimum diameter, and volume with standing crop and canopy cover show mesquite had little infhtence on individual perennial grasses, total perennial grasses, non-poisonous forbs, broom snakeweed or other shrubs on either treated or non-treated areas


• Total grass standing crop means for data pooled across periods were 1,593 and 1,494 kg/ha for moderate and low mesquite levels, respectively. These forage estimates are substantially higher than those from other Chihuahuan desert studies (Paulsen and Ares 1962, Herbel et al. (1983). We explain our high forage levels by well above average growing season precipitation for the 1984-1992 period, above average winter rainfall in 1991 and 1992, favorable soil, and low stocking rate.


• we compared our 1992 mesquite density and canopy cover data with that collected on the same areas in 1952 by McNeely (1983). These data show mesquite densities and canopy cover increased more on low than on moderate mesquite areas


• These observations tend to further confirm that mesquite has small impact on forage production at cover levels below 17%.


• Many range researchers in the southwestern United States have considered mesquite invasion a major threat to livestock grazing Gibbens et al 1992). Our research is somewhat inconsistent with these observations.


• Mesquite dominated ranges to improve without woody plant con-trol (Glendening 1952, Paulsen 1953, Herbel et al 1983, Gibbens et al. 19S6). Although research is limited, experimental evidence does indicate that grazing management and climatic trends may have more influence on the status of perennial grasses than increases in mesquite.


• mesquite) increases may be at least partially due to their very from the intense drought in the 1950?s (Betancourt et al. 1993). On Arizona desert range over a 28 year period (1941- 1969)


• Eight years after spraying with 2,4,5-T moderate-ly stocked, deferred-rotation grazed pastures had 4 times the mesquite canopy cover of heavily stocked continuously grazed pastures. However, perennial grass production across three sites was 47% higher under moderate, deferred rotation compared to heavy, continuous grazing (1,413 vs 959 kg/ha).


• Method of grazing had more influence than woody plant con-trol on forage productivity in McNeely?s (1983) study


• Black grama, dropseeds, and threeawn all showed major increases in production between 1968 and 19S2 on moderately stocked con- tinuously grazed areas both with and without herbicide control. However, perennial grass production generally decreased on sea-sonally grazed areas.


• In recent years there has been a widely held view that grazing management alone has minimal potential to increase forage pro- duction on arid rangelands dominated by brush (Westoby et al. 1989, Laycock 1991). Although we acknowledge such situations, we believe they are more the exception than the rule. We support this conclusion with broad long-term studies from the Chihuahuan desert (McCormick and Galt 1993). and Salt desert (Yorks et al. 1992) as well the present study. These studies all show major increases in forage plants and improvement in range condition over 30-40 year periods if grazing intensities were moderate and precipitation was average or above average follow- ing drought.


• Our study tends to provide support for the basic successional model of Clements (1916) and Dyksterhuis (1949) in which cli-mate and grazing push the system either towards or away from climax. However, we do not reject that state-and transition model of Westoby et al. (1989). We believe if mesquite canopy cover levels were greater and if the seed source of perennial grasses was severely depleted meaningful range improvement would be unlikely.


• However, mesquite has some positive effects on forage plants. It provides grasses and forbs with enhanced soil nutrients (especially nitrogen because mesquite is a legume) and grazing protection (Wooten 1916, Buffington and Herbel 1965, Martin and Cable 1974).


• The simultaneous increases of mesquite and perennial grasses in our study are consistent with long term studies by Potter and Krenetzky (1967), Smith and Schmutz (1975), and McNeely (1983).


• Mesquite canopy cover ranged from 0 to 37% on our sample plots. Scifres and Polk (1974) found it difticult to mea- sure significant forage increase on mesquite control areas where mesquite canopy cover was less than 15-20%. However, honey mesquite canopy cover above 15-20% appears to negatively impact perennial forage cover based on studies from Texas (McDaniel et al. 1982) and Arizona (Glendening 1952). However this will very likely be site dependent


• Mesquite control at the levels we studied in the Chihuahuan desert does not appear to cause enough increase in forage production to offset treatments costs and risk at current cattle prices (Holechek 1992, Holechek and Hess 1994).