USING HISTORIC DATA TO ASSESS EFFECTIVENESS OF SHRUB REMOVAL IN SOUTHERN NEW MEXICO

Authors: Rango, Albert; HUENNEKE, LAURA - NEW MEXICO STATE UNIV; BUONOPANE, M - NEW MEXICO STATE UNIV; Herrick, Jeffrey - Jeff; Havstad, Kris

Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2004
Publication Date: 7/1/2005
Citation: Rango, A., Huenneke, L., Buonopane, M., Herrick, J.E., Havstad, K.M. 2005. Using historic data to assess effectiveness of shrub removal in southern New Mexico. Journal of Arid Environments. 62(1):75-91.

Interpretive Summary: The only effective way to assess long-term shrub treatments in grassland areas is to examine any treatments that were performed 50-60 years ago. The problem is that the original records have been lost and even the locations of the treatments are no longer known. We closely examined historic file records and acquired historic aerial photography from the 1930's for the Jornada Experimental Range and Chihuahuan Desert Rangeland Research Center and then, using both sources, found the location of treatments performed in 1936-1937 as well as transects and quadrats that had been lost. Once located, we made the same measurements as the original investigators and made some supplemental measurements as well. We were able to conclude that the effects of shrub removal had little effect on reestablishment of grass cover after 65 years. In fact, the shrubs seem to be continuing to invade the former grassland areas. These results should be useful to operational agencies such as NRCS and BLM, state agencies, and ranchers.

Technical Abstract: In the late 1930's, the presence of a highly organized labor force, the Civilian Conservation Corps (CCC), in the Jornada Basin of southern New Mexico provided the capability for rangeland scientists to conduct experiments to determine the effectiveness of various techniques for remediating or reversing the encroachment of shrubs into grasslands. Unfortunately, soon after the treatments were performed, the CCC disbanded and most records of the treatments were lost. Despite sketchy documentation, some rangeland treatments left legacies on the landscape, and effects on water retention, erosion, and vegetation dynamics remained long after the CCC work ended. The discovery of historical documents from long-closed files and aerial photography in widely scattered archives allowed some of the experiments to be located and reexamined. Two research areas established in the mid-1930s were of particular interest, namely a tarbush (Flourensia cernua) site where shrubs were grubbed and quadrats established and a creosote (Larrea tridentata) site where both creosote and tarbush shrubs were grubbed. Here we outline how these sites were rediscovered, how historical measurements were repeated for the first time since the late l930s, and conclusions drawn regarding specific rangeland remediation strategies and vegetation dynamics. Our results show that shrub populations recovered from a radical removal treatment in less than 65 years. Remediation of these sites so that grass will recover to pre-shrub-dominated amounts will require measures additional to just removal of shrubs in order to restore hydrologic function. The fact that we were able to relocate, revisit, and resample these treatment areas provided unique opportunities to understand the long-term vegetation dynamics of these arid ecosystems. It is evident that woody plant populations have a high degree of resilience, that density dependence or interference appears to limit plant size in arid shrub communities, and that shrub populations had not reached any stable equilibrium state at the time of treatment in the 1930s. These insights would have been impossible to gain from short-term studies and without long-term studies initiated in the 1930s combined with recent discoveries of original documentation and historical aerial photography.