Ecological restoration needs derived from reference conditions for a semi-arid landscape in Western Colorado, USA

Semi-arid ecosystems cover tens of millions of hectares in the Intermountain West of the United States, and most have altered plant communities due to land use, especially livestock grazing. Thus, relatively unaltered “reference” plant community information is needed to guide restoration. Plant communities were sampled over a large ( 600 000 ha) semi-arid landscape in western Colorado, within piñon–juniper woodlands, sagebrush shrublands, and grasslands, and over conditions ranging from relict areas without livestock grazing to heavily utilized areas. Ordination was used to group samples into ranked categories of ecological condition within 18 communities, and means–tests and other techniques were used to identify ecological differences among ranks across vegetation types. With few exceptions, grass and forb cover, biological soil crust cover, and species diversity declined concomitant with ranks representing increasingly degraded conditions, while non-native species cover was variable among ranks. Landscape-level species abundance patterns also differed significantly among ranks, with herbaceous species generally exhibiting less constancy and cover within degraded samples compared to samples of reference quality. These semi-arid ecosystems will require both active (e.g., reseeding) and passive (grazing management) restoration approaches, at local- and landscape-levels, respectively, if the goal is to restore native plant composition and abundance.