Jornada Basin LTER

Desertification: Local Research Fosters Global Problem Solving

Desertification, the degradation of terrestrial ecosystems to the point where structure and function of an ecosystem resemble those of arid lands, is a problem of global significance. Currently one third of the earth's land surface is classified as semiarid or arid, and a substantial portion of the human population relies on those lands for subsistence.

Both the long time scale of land degradation processes, and the large spatial scale necessary for studying the variable and sparse ecosystem elements of semiarid systems will require long-term research efforts such as the Jornada Basin LTER, which are essential for understanding ecosystem problems.

In the southwestern U.S. and northern Mexico, desertification has resulted in the loss of extensive perennial grasslands and their replacement by desert shrublands dominated by mesquite and creosotebush. The Jornada Basin of southern New Mexico has long been a major site for research relevant to desertification processes and their consequences. Given the long response time of many elements of the system, the existence of this long-term site has been crucial to documenting changes in ecosystem structure and responses to human activities in the landscape.

Temporal Changes in plant communities on the Jornada Experimental Range
Reconnaissance surveys were made by the Forest Service to determine the number of forage acres on the plains portion of the Jornada Experimental Range in 1915-16 and 1928-29. Vegetation type maps were prepared from the surveys and these maps have been digitized so that they may be compared to a vegetation type map made utilizing aerial photographs and field reconnaissance in 1998. More area was fenced in 1915-16 than at present, but only area show by dotted lines and conforming to present boundaries was used in computing the areas for the various vegetation types shown in table. Only the primary dominants given in the 1915-16 survey are shown. The areas dominated by mesquite in 1998 were categorized as mesquite (soil accumulations at base of plants 20 cm or less), mesquite dunes (20 cm to about 3 m in height), or mesquite sandhills (greater than 3 m in height, sometimes 6 m or more).

The resource redistribution/increasing heterogeneity model of desertification has served as a key conceptual model for researchers in semi-arid ecosystems around the world. The model has focused attention on the concentration of soil resources beneath shrubs, and the formation of open or bare inter-plant spaces, as the crucial step increasing the impact of abiotic factors (e.g., agents of erosion). Productivity in semi-arid systems is so patchy and variable in time that it is impossible to assess the degree to which desertified systems actually have decreased in primary production without long-term data. Intensive sampling in the Jornada Basin over 10 years demonstrated that in fact relict grasslands tend to have significantly higher aboveground NPP than do desertified shrublands.

The resource redistribution model has found a number of applications to management, monitoring, and remediation in semi-arid rangelands. Long-term ecological and management records from the Jornada Experimental Range and LTER created the unique opportunity to test the use of higher-resolution remote sensing data in the challenging environment of dryland systems. The same long-term history of manipulations and archival of methods and data from the Jornada Basin is proving essential to efforts ranging from evaluating potential for soil carbon sequestration in rangelands to modeling potential response of semi-arid systems to climate change.