Controls of Carrying Capacity: Degradation, Primary Production, and Forage Quality Effects in a Patagonian Steppe

GOLLUSCIO RA; BOTTARO,H.; OESTERHELD M

Rangeland Ecology and Management (ex JRM)

SOC RANGE MANAGEMENT

Lugar: Boulder, Colorado; Año: 2015 vol. 68 p. 266 - 275

1550-7424

Rangeland carrying capacity depends on aboveground net primaryproduction (ANPP) and on the sustainable harvest index (HIsust), the portion ofANPP that livestock can consume without undermining the production capacity ofthe system. At a regional scale, the observed harvest index (HIreal) increaseswith ANPP, but at a landscape scale the pattern is less clear, and controls ofHIreal and HIsust are unknown. We analyzed the landscape patterns of variationof HIreal and HIsust across gradients of ANPP, pastoral value of vegetation(PV), and degradation. In 15 plots of a 2 753-ha paddock in a westernPatagonian grass?shrub steppe, we estimated ANPP, consumption, forage pastoralvalue, and degradation. To estímate degradation we used PV weighed by foragecover because it was negatively correlated with a combination of ecosystemtraits formerly linked to grazing-induced degradation. We calculated HIreal(consumption/ ANPP) and HIsust (consumption removing 40% of aerial biomass ofthe key species/ANPP). We choose Festuca pallescens as the key species becauseof its high abundance and moderate preference. As the paddock was grazed withlow stocking rate to maximize among-plots selection, HIreal was lower thanHIsust. As in regional models, HIsust and HIreal increased with ANPP within thepaddock (R2 = 0.33 and 0.30, respectively). Multiple regressions showed thatHIreal increased with ANPP and degradation, while HIsust increased with ANPPbut decreased with degradation (R2 = 0.64 and 0.77, respectively). Thissuggests that at stocking rates lower than carrying capacity, sheep choose highlyproductive stands and, at a given level of ANPP, they prefer degraded stands.In contrast, carrying capacity increases with productivity and decreases withdegradation. Management systems based on HIsust may result in severe biomassremoval of species more preferred than the key species (Poa ligularis), and itis necessary to include strategies to preserve their individuals andpopulations.