Polylepis mountain woodland of central Argentina: Livestock rearing, fires and woodland distribution.

DANIEL RENISON; ANA M. CINGOLANI; ISABELL HENSEN; ROMINA C. TORRES; JULIETA ALINARI

San Carlos de Bariloche. Río Negro.

Taller; Workshop on forest fragmentation in South America.; 2006

Red Latinoamericana de Restauración Ecológica

Mountain forests are often inaccessible, sparsely populated and are often believed to be relatively pristine environments where human influence is negligible and good opportunities exist to study natural processes. However, this concept is being challenged and the issue of whether humans have, or have not, had a considerable influence remains controversial (Kessler, 2002; Sarmiento, 2002). Because livestock rearing is the main economic activity in most of South American mountains and almost always associated to burning to promote grass re-growth, since 1997 we have been studying the long and short term effects of livestock and fires on the development of Polylepis australis (Rosaceae) woodlands in Central Argentina. Here the human-natural influence on Polylepis woodlands is yet controversial to a certain extent, as livestock breeders, scientist and managers have differing opinions. P. australis is the dominant species of the woodland canopy, harbors a high richness of endemic species and is usually associated to deep ravines and rocky areas. Our main results suggest that the present distribution, degree of fragmentation and woodland structure is mainly due to human influence and natural features have a secondary role through their influence on human caused disturbances (Renison et al. 2006). Fires are less prone to affect deep ravines and rocky areas (Renison et al. 2002, 2006). Fire scars were present in 70 % of our 146 study plots. When trees are burnt around 70% survive by re-sprouting forming multi-stemmed shrubs, however the high incidence of human caused fires does not allow the development of mature forests, which are almost absent. Uneven browsing by free ranging livestock results in the retreat of woodlands in accessible areas and microsites. When accessible, P. australis is so heavily browsed that it cannot regenerate (Teich et al. 2005). Livestock is also the main triggering factor of soil erosion (Renison et al. submitted) which in turn reduces P. australis reproductive output (Renison et al. 2004). Because both fires and livestock affect woodlands differentially according to topographic features, an association between topographic features and woodland distribution cannot be taken as evidence for a purely natural process with no human intervention, an error which has caused confusion in the general public, livestock breeders, scientist and managers. Implications: (1) livestock must be carefully managed to permit woodland regeneration and avoid soil erosion; (2) forestation with P. australis can be considered as a restoration objective even when done out of deep ravines and rocky areas.