Combined effects of fire and cattle in shrublands and forests of northwest Patagonia

Abstract

Ecología Austral, 25:1-10 (2015)

In northwest Patagonia, the two most pervasive disturbances at the landscape and community levels are fire and herbivory by introduced ungulates. There is a long history of fire in the region, but repeated fires followed by heavy browsing constitute a new type of disturbance regime in these landscapes. Our objective was to analyze different micro-environmental variables and plant community parameters at sites affected by the combination of both disturbances. We studied 17 sites within Nahuel Huapi National Park, classified according to fire and herbivore history: not burned (>50 years) or recently burned (<15 years); and free of livestock or alternatively under heavy browsing. We found a strong effect of time since fire and a slighter effect of cattle. The combination of both disturbances only had a synergistic effect on humidity (during hours of higher temperature occurrence) and on solar radiation, and consequently an increase in adverse environmental conditions was observed at recently burned sites and with cattle present. Additionally, total cover of woody and semi-woody species decreased at sites affected by both disturbances. Maytenus chubutensis and Rosa rubiginosa characterized unburned sites; and indicator species at sites without cattle and with cattle were Ribes magellanicum and Berberis darwinii,respectively. Through different mechanisms, fire and cattle modify community characteristics, and when both disturbances co-occur, in some cases they can synergistically affect the plant communities, exacerbating xeric conditions which may accelerate land degradation. By increasing knowledge of indicator species and their associated site conditions, we can provide basic information for restoration guidelines, conservation, and sustainable management of Patagonian forests and shrublands.