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

GRAU, HECTOR RICARDO; CARILLA, JULIETA; GIL-MONTERO, RAQUEL; VILLALBA, RICARDO; ARAOZ, EZEQUIEL; MASSE, GLADYS; MEMBIELA, MONICA DE

Mountains in the Mist

Cambridge University Press

Lugar: Cambridge, UK ; Año: 2010; p. 1377 - 1399

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.  This paper combined historic analysis of land use and 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 20th 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 20th 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.  The increase in rainfall and decrease in grazing intensity is negatively associated with tree recruitment, particularly in the case of Podocarpus parlatorei, the dominant tree species in adjacent secondary forests.  The interpretation offered here is that decreased grazing and increased rainfall has favored grassland over shrubland.  Grasslands are maintained with frequent fires, which eliminate 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 very light-demanding tree species, recruits.  This study suggests that feedbacks between fire, land use, climate, and vegetation may promote resistant degraded grasslands that are not invaded by forest species even when land use intensity decreases and climatic conditions become favorable for tree establishment.