Effects of cattle crazing on early postfire regeneration of matorral in northwest Patagonia, Argentina

In the National Reserve sector of Nahuel Huapi National Park, southwestern Argentina. livestock are potential threats to native plant biodiversity and may prevent postfire recovery of shrublands. Effects of cattle grating wer e examined in a recently burned shrubland (matorral) by installing livestoc k exclosures and permanent plots and remeasuring vegetation over a 3-year p eriod. Percentage cover of all vascular plant species, and maximum heights of all shrub species, were recorded in ten 25-m x 25-m plots from late summ er of 1995 to 1997. Five of the plots were fenced and five were left access ible to low-intensity browsing and grazing by cattle. A substantial decline in total species richness, especially shrub species, was attributed to gra zing. Under this relatively low level of cattle grazing pressure, frequency and cover of common shrubs and trees were significantly reduced. In contra st, height growth of shrubs and trees was not significantly affected. Facil itative interactions (e.g., nurse effects of shrubs on the vegetative repro duction of other plants) are important in these shrublands. Consequently, a n initially slight reduction in abundance of key shrub species creates the potential for more severe long-term reductions in biodiversity.