Influence of deferred grazing on vegetation dynamics and livestock productivity in an Andean pastoral system.
Abstract
Management recommendations intended to reduce rangeland degradation and increase livestock productivity often assume equilibrium conditions wherein vegetation and herbivore dynamics are tightly coupled. Recent research in Africa, Asia and North America, however, suggests that the dynamics of some arid systems are driven more by precipitation, a non-equilibrium factor. We examined the applicability of equilibrium and non-equilibrium theory for key grazing resources within an Andean pastoral ecosystem. Residents of Cosapa, Bolivia, recently fenced off portions of critical communal grazing areas called bofedal (wet meadow) and gramadal (dry meadow) as part of a livestock development project. Fenced exclosures were used to implement seasonally deferred grazing practices. We evaluated the effects of deferred grazing on peak standing crop (SC), above-ground net primary production (ANPP) and plant species composition and diversity over a 4-month growing season across 10 locations. Effects of exclosure access on the productivity of alpaca Llama pacos, llama L. glama and sheep Ovis aries were assessed through interviews with 32 herd owners. One to three years of deferred grazing had no effect on SC or ANPP from bofedal or gramadal, but it did reduce plant species diversity for bofedal. Access to exclosures improved survival rates of young alpaca and birth rates for sheep. Llamas were typically denied access to exclosures, which negatively affected their productivity. Our results suggest that both non-equilibrium and equilibrium forces operate on bofedal. Stable and low rates of ANPP are largely shaped by the cold climate, a non-equilibrium factor. Changes in plant species composition and livestock productivity, however, support equilibrium theory. Synthesis and applications. Ecological models of rangeland dynamics often play a critical role in determining the direction of range management and pastoral development. On bofedal, we found that vegetation and herbivore dynamics are coupled to a large extent, consistent with predictions that equilibrium behaviour can occur for critical, mesic subsystems nested within arid landscapes. Seasonal grazing deferral on bofedal can thus yield benefits to livestock productivity. However, these benefits must be weighed against negative social consequences that can occur when communal resources are privatized.