Environmental history and forest regeneration in a degraded valley in the subtropical Argentina cloud forest life zone

GRAU, H.R.; CARILLA, J.; GIL MONTERO, R.; VILLALBA, R.; ARAOZ, E.; MASSE, G.; MEMBIELA, M.

Tropical Montane Cloud Forests: Science for Conservation and Management

Cambridge University Press

Lugar: Cambridge; Año: 2010; p. 597 - 604

Extensive areas of montane cloud forests have been transformed into degraded grasslands due to intensive land use in the past. As a consequence of economic modernization and rural-to-urban migration, land-use intensity is decreasing in many of these areas. This chapter combines analysis of historic land use with dendrochronologic estimates of climate, fire, and tree establishment to explore the interactions between climate, socio-economic changes, and vegetation dynamics in a degraded valley in the cloud forest life zone of NW Argentina. During the twentieth century,population increased and became concentrated in the local capital township. State and services employment increased while density of domestic grazers decreased in the second half of the century. Rainfall increased; the period post 1970 was moister than the previous 250 years. Despite these trends, secondary tree species are not colonizing degraded grasslands in this area.The increase in rainfall and decrease in grazing intensity is negatively associated with tree recruitment, particularly with respect to Podocarpus parlatorei, the dominant tree species in secondary forests adjacent to pasture. The interpretation offered here is that decreased grazing and increased rainfall has favored grassland over shrubland. Grasslands are maintained by frequent fire, which eliminates Podocarpus seedlings and unpalatable shrubs that, in turn, facilitate Podocarpus recruitment by providing perches for seed dispersal and generate a less stressful micro-environment. Only in particular years following periods of intense fire activity, Alnus acuminata, a highly light-demanding tree species, recruits. This study suggests that feedbacks betweenfire, land use, climate, and vegetation may promote resistant degraded grasslands that do not become invaded by forest species even when land-use intensity decreases and climatic conditions become favorable for tree establishment.