Effect of the reintroduced guanaco vs. domestic livestock herbivory over the lawns of the Quebrada del Condorito National Park

Abstract

The Quebrada del Condorito National Park was created to protect a high-elevation ecosystem that experienced severe degradation due to centuries of overgrazing. For this reason, domestic livestock was partially excluded from the area since 1999. However, the absence of largescale herbivory led to the encroachment of Poa stuckertii thick grasslands over grazing-lawn patches, risking their high biological diversity. To reverse this situation, in 2007 the guanaco (Lama guanicoe) was reintroduced. This is a low-impact wild herbivore that was locally extinct at the beginning of the 20th century. In this study, we compared interannual changes (2016-2017) in different types of cover present in the study area (thick tussock grasses, thin tussock grasses, short vegetation, and surface without vascular vegetation) between four paddocks with different grazing conditions: 1) grazing by domestic livestock and guanacos; 2) grazing by domestic livestock; 3) grazing only by guanacos; and 4) complete exclusion of large herbivores. We observed that grazing by reintroduced guanacos, at their current densities, does not alone limit the spread of thick grasses, promoting the persistence of grazing-lawn patches, whereas, in contrast, grazing by domestic livestock produces a slight reduction in thick tussock grasses. Therefore, to conserve grass patches, it will be necessary to combine moderate densities of domestic livestock, avoiding to provoke erosion, with grazing by reintroduced guanacos. Additionally, it is necessary to reinforce the guanaco population until it reaches a size large enough to asses whether they can prevent thick tussock grasses from invading the grazing-lawns and permanently exclude domestic livestock.