Productivity, management and development problems in the arid rangelands of the central Mendoza plains (Argentina)

The central Mendoza plains (56,000 km(2)), located in the eastern foothills of the Andes, belong to the vast phytogeographic province of 'Monte' (c. 500,000 km(2)) in Argentina. This area is a typical warm arid zone and vegetation is typically a shrubland. Perennial grasses are predominantly C-4 species. Land-use is for livestock grazing; the average stocking rate is 28 ha per large stock unit (LSU), year-long. Ecological and range research have been actively pursued in the region by IADIZA over the past 25 years. Two experiment stations were established 25 and 10 years ago, respectively: The Nacunan Biosphere Reserve and the El Divisadero Cattle and Range Station. Primary production and its relationship to climatic and edaphic parameters were analysed and compared in the two stations. Rain-use efficiency (RUE, kg DM ha(-1) year(-1) mm(-1)) and useful rains efficiency (URE, P-0.1 PETp) were similar in both cases (RUE 1.7 and 2.0; URE = 3.0 and 2.9, respectively), when herbs are concerned. However, the variability of annual production was much higher on the silty soils of Nacunan than on the coarse sands of El Divisadero; PRVR (Production to Rain Variability Ratio) was 2.5 and 0.53, respectively. Utilization of such experimental figures allows for the prediction of primary production and carrying capacity for a given year, based on rainfall probabilities and, therefore, to determine stocking rates in a rational manner. Basing stocking rates on annual dependable rains (f 0.8) and on useful rains probability (P-0.1 PETp) proved to be a sound and realistic assessment, validated by long-term experiments and experience. The results of the studies on brush control, cattle diet composition, animal productivity and feed value of forage species were analysed. Current and future research programmes in IADIZA for the Mendoza plains are mentioned. Although research on resource inventory and basic ecological processes in the Mendoza plains should carry on, the emphasis and therefore the resources should henceforth be devoted to the consequences of resource management alternatives on overall arid land productivity, i.e. research for development. A better integration of applied ecology for management and investigations on basic arid land ecological processes should appear in IADIZA programmes. (C) 1997 Academic Press Limited.