Grazing distribution of wild guanacos and livestock in Patagonian rangelands: an ecological approach to assess mixed carrying capacity and overgrazing risk in extensive pastoral systems

Abstract

Context: Along with forage availability, rangeland’s carrying capacity (CC) is determined by other landscape features limiting the spatial distribution of the animals, such as water sources or topography. However, livestock management is often based on the stock adjustment to an estimated CC, assuming that the animals use the entire paddocks and wild herbivores are absent. Objectives: Our objectives were to address how the CC estimation deviates from the classic outcome when the effective space use by livestock is considered, and when the forage consumption by co-occurring wild herbivore is accounted for. Finally, we evaluated large herbivores densities regarding this mixed CC. Methods: Based on herbivore counts and geo-referenced explanatory variables within a ranch of Chubut, Argentina, we predicted sheep and guanaco distribution at a scale of 0.25 km2 cells. Addressing the relationship between the predicted sheep stock and the CC in each cell, we then re-calculated the CC adjusted by spatial use. We also estimated a mixed CC by computing the forage consumption by sheep and guanacos. Results: Sheep distribution was shaped mainly by drinking water location, promoting over and under-grazed areas. Guanaco distribution pattern opposed livestock density. Accounting for the restrictions in sheep spatial use resulted in a reduction of the estimated CC compared to the classic approach, whereas the mixed approach resulted in higher CC estimates. Conclusions: Accounting for herbivore presence and distribution modifies the CC estimation and therefore the diagnosis of overstock situations. The proposed adjustments to CC assessment methods can contribute to the sustainable management of livestock and wildlife in rangelands.