摘要：Native grasslands worldwide have been degraded by grazing, but the processes involved have been studied insufficiently.Grasslands were a major habitat on the southern section of the Mexican Plateau when the Spaniards arrived 500 years ago.Since then, they have been impacted heavily through grazing, but the details and history of such impacts have not been established.We aimed at untangling almost 500 years of grazing of these grasslands, based on extensive searches of published information and of documents in historical archives.We identified three periods of ranching: Cattle, from the mid-16th to the mid-17th Centuries; sheep, reflecting a change from tall to short grasses; and, finally, goats and horses, along with sheep, asses and some cattle, after serious grassland degradation by the mid-20th Century.Overgrazing has impacted grassland composition in the region and its capacity to support livestock, but also, strongly affect some 20 species of native vertebrates and an unknown number of plant and invertebrate species.The current condition of some ranges and a livestock exclosure indicate that grassland improvement is possible, but realistic objectives based on biodiversity conservation and livestock production should be targeted, rather than utopic pre-livestock frameworks.Grasslands in the region at the time of Spanish arrival possibly had a mixture of grasses and herbs, but buffalo grass and the central Mexico tobosa grass are potential initial range management targets for grassland recovery of the ranges in worst condition, while blue gramma and the Mexican plateau gramma are good targets for ranges that still have some grass cover.
关键词：Landscape history;Overgrazing;Grazing;Environmental degradation;Conservation;Llanos de Ojuelos;
