Do domestic herbivores retard Polylepis australis Bitt. woodland recovery in the mountains of Córdoba, Argentina?

Herbivores are often an important factor hindering the recovery of woodlands. Browsing generally retards seedling and juvenile tree growth, but the exact impact of herbivores is still controversial. The high mountain areas of central Argentina consist of a mosaic of Polylepis australis Bitt. woodlands and different grassland types which are grazed by large domestic herbivores. To contribute to the management of these ecosystems, we performed an observational and an experimental study. In the first, we measured P. australis browsing intensity and size structure in areas with sparse woodland cover under two treatments. One treatment consisted of seven areas with high stocking rates, and the other consisted of five areas where livestock were reduced to low or moderate stocking rates 6-7 years prior to our measurements. In the experiment, we planted P. australis seedlings in a heavy grazed and an ungrazed area and measured growth and survival during 6 years. Our observational study showed that livestock browse heavily on P. australis, but a reduction of livestock densities reduced browsing rates and changed population size structure. The experimental results confirmed the high browsing rates, and showed that browsing negatively influences survival and height-growth. Our data suggests that heavy grazing by domestic herbivores retard P. australis woodland recovery, but a reduction in stocking rates promote changes that can lead to an increase in P. australis density. An adequate livestock management is therefore very important in the mountains of Córdoba.