Almost one third of Argentina is included in the Chaco region of South America. Climate features shift from humid in the East to arid toward the West, with rainfall mainly during the summer months. Winter is dry and cold, with frosts sometimes reaching -15° C. The topography is gentle: only some ‘sierras’ break the landscape in the southwestern Chaco. In the center of the region, where the Santiago del Estero Experiment Station is located, soils belong to the Aridisol and Mollisol orders.
Vegetation of the Chaco region is a mixture of savannas, thorn shrublands and hardwood forests alternating in belts and patches. Species present belong to the following genera: Schinopsis, Aspidosperma, Prosopis (trees); Celtis, Atamisquea, Larrea (shrubs); Elionorus, Setaria, Trichloris, Heteropogon, Botriochloa, Digitaria (grasses); Wissadulla and Justicia (broadleaves). Evidence suggests that fire has been a natural component of the Chaco ecosystem for thousands of years. Indians used fire for warfare and hunting; in fact, “Chaco” means “a site for hunting” in the Quichua language. Fire swept across the savannas and shrublands and on some occasions hit the hardwood forest that burned with high intensity. Tolerance of species to fire is mixed. The fire cycle is estimated to be around 3-5 years in savannas.
Although ranches existed in the region since the very beginning of the Spanish settlement (XVI Century), extensive cow-calf and timber operations began in the mid XIX century largely due to European immigration. The practice of setting fires — without too much concern about the consequences, as everywhere in the world — is traditionally used by rangers to promote new growth in early spring, or to ‘clean’ native ranges. Coupled with overstocking, it led to savanna encroachment by Acacia, Celtis, Schinus and other shrubby/spiny species. Severely logged hardwood forest sites have been also invaded by early succession species and kept at this stage by overgrazing.
Nowadays, fires in this region are originated mainly by rangers’ and farmers’ activities. The 1993 winter (June to September) was a specially remarkable fire season: almost 100,000 ha were burned in the southwestern Chaco region. In the southern tip, almost 50,000 ha of mid-altitudinal palm savannas also burned. An extremely dry and cold winter was the main cause of these large fires.
In 1991, the Santiago del Estero Experiment Station, belonging to the INTA (National Institute for Agriculture and Livestock Technology) network, started research in fire ecology and prescribed fire. Due to the fact that the regional ecosystem has envolved with fire, the main working hypothesis is that prescribed fire in savannas, together with other range management practices, may benefit the livestock industry.
Field research is conducted at two levels or ‘scales’: basic work is conducted at the 7,000 ha Experimental Ranch; and adaptive research at private ranches. Objectives of the first approach are to develop prescriptions to control Acacia aroma and other shrubs with fire, and also to understand some basic facts about fire effects on grasses and broadleaf species, and on the nitrogen cycle through the study of the soil microbiology. A year of research (1993) is already completed, and data about fire intensity, fire spread, etc. are being processed. Three more seasons of work are already planned ahead. On the other hand, adaptive prescribed burning has been conducted since 1991 in several private ranches in cooperation with Extension Agencies depending on the Research Station. Almost 2,000 ha of native and exotic pastures have been burned, using Wright and Bailey’s (1982) prescriptions as reference.
Results so far suggest that prescribed burning could be an effective management tool for native rangers. However, more research should be conducted in order to integrate some features of prescribed burning into the ranching operations on a yearly basis.
From: Carlos Kunst Address: INTA EEA Sgo del Estero CC 268 – Jujuy 850 ARG – 4200 Santiago del Estero