|Gibbens, R - USDA-ARS RETIRED|
|Mcneely, R - NEW MEXICO STATE UNIV|
|Beck, R - NEW MEXICO STATE UNIV|
|Nolen, B - NEW MEXICO STATE UNIV|
Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 21, 2004
Publication Date: June 1, 2005
Citation: Gibbens, R.P., McNeely, R.P., Havstad, K.M., Beck, R.F., Nolen, B. 2005. Vegetation changes in the Jornada basin from 1858 to 1998. Journal of Arid Environments. 61(4):651-668. Interpretive Summary: Vegetation changes over a 140-year period (1858 to 1998) have been documented on two large rangeland research stations in the northern Chihuahuan Desert. The USDA Agricultural Research Service's Jornada Experimental Range and the New Mexico State University, Department of Animal and Range Science, Chihuahuan Desert Rangeland Research Center are adjacent facilities in the Jornada Basin of southern New Mexico. Vegetation maps were constructed from records of land surveyor notes in the mid-1800's. These maps were compared to a modern map over 84,270 ha (21,0675 ac) constructed from modern aerial photography and ground surveys in 1998. Prior to widespread, heavy livestock grazing in region during the late 19th century, much of this area was desert grassland. By the latter part of the 20th century, most of the region was then dominated by three native, woody shrub species, especially honey mesquite. Though mesquite was widespread in the region in the 1800's, it was dominant on about 6 percent of this landscape. However, because of earlier heavy livestock use and period droughts, especially the megadrought of the 1950s, mesquite now dominates on about 53 percent of the total area surveyed. Vegetation change of this nature and extent, especially from grassland to shrubland, is characteristic of arid regions throughout North America and the world. Much of this change has been driven by excessive use during prior centuries. However, some change of this nature would be expected in response to climatic variation and extreme episodes, such as prolonged drought. Shrubs such as mesquite would likely be dominant on more areas today than during the 19th century even without livestock grazing, but the extent and density would not have been nearly as great as what is seen in current times. Without management and specific efforts to control further shrub encroachment remaining desert grasslands will be further lost throughout this region.
Technical Abstract: Notes made by land surveyors in 1858 were utilized to estimate cover of grasses and shrubs on the Jornada Experimental Range (JER) and the Chihuahuan Desert Range Research Center (CDRRC) in the northern Chihuahuan Desert, southern New Mexico, USA. Portions of these areas have previously been assessed for historical vegetation dynamics, but the entire 84,271 ha assessed in the 19th century has not been examined in total. In 1858, fair to very good grass cover occurred on 98 and 67 percent of the JER and CDRRC, respectively. Shrubs were present throughout both properties, but 45 percent of the JER and 18 percent of the CDRRC were shrub free. Reconnaissance surveys to determine carrying capacity for livestock, made in 1915-16 and 1928-29 on the JER and in 1938 on the CDRRC, show that shrubs had made large increases in area occupied at the time of the surveys. Vegetation-type maps were made of both properties in 1998. Mesquite (Prosopis glandulosa Torrey) was the primary dominant on 59 percent of the JER in 1998, and creosotebush [Larrea tridentate (Sess. & Moc. Ex DC.) Cov.] was the primary dominant on 27 percent of the area. On the CDRRC, mesquite and creosotebush were primary dominants on 37 and 46 percent of the area, respectively. Grass cover has decreased greatly with the increase in shrubs, and only shrub control efforts have maintained the once abundant black grama [Bouteloua eriopoda (Torrey) Torrey] as a primary dominant on 1 percent or less of the area on both properties. Sustainable use as grazing land will require low levels of use because grasses cannot increase unless shrubs are eradicated and shrub control is likely to remain economically unfeasible for the foreseeable future.