Environmental history and forest regeneration dynamics in a degraded valley of NW Argentina

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

Hawaii

Congreso; Mountains in the mist; 2004

University of Hawaii

Extensive areas of cloud forests have been transformed into degraded grasslands due to intense 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.We combined theorical analysis of land use and dendrochronological estimates of climate, fire and tree establishment to explore the interactions between climate, socioeconomic changes and vegetation dynamics in a degraded valley in the cloud forest life zone of NW Argentina. 20th century population increased and became concentrated in the local capital townships.State and services employment increased while density of domestic grazers decreased in the second half of the 20th century. Rainfall increased; the period post 1970 was the moister of the past 250 years. Despite these trends, the most abundant secondary species are not colonizing degraded grasslands.The increase in rainfall and decrease in grazing intensity is negatively associated to tree recruitment, particularly in the case of Podocarpus parlatorei, the dominant tree species in secondary forests. We interpret that decreasing grazing and increasing rainfall favored grasslands over shrublands. Grasslands are maintained with frequent fires, which eliminate Podocarpus seedlings and unpalatable shrubs that facilitate Podocarpus dispersal. Only in particular years following periods of intense fire activity, Alnus acuminata, a very light-demanding tree species, recruits. Our study suggests that feedbacks between fire, land use, climate, and vegetation may promote resilient degraded states that will not recover even when land use intensity decrease and climatic conditions become favorable for tree establishment.