Grassland–shrubland transformation and grazing: A century-scale view of a northern Chihuahuan Desert grassland

Abstract

We assessed vegetation change from the 1800s to late 1900s in a Chihuahuan Desert grassland and examined grazing effects. The study area was grazed until 1943 when livestock were removed from a portion. This enabled us to examine shrubland invasion in a historical grassland, relative to continuous grazing and exclusion. Shrublands invaded most of (87%) the sample units, 66% became at least half shrubland, and mean grassland patch size fell 90%. Shrublands invaded more sample units in the grazed site than exclosure (94% vs. 80%), and 22% more grazed site units were very highly invaded (at least 95% shrubland). Grazed site patch size decline was higher, on average, than exclosure patch decline. Results corroborate regional grassland loss and forewarn remaining study area grasslands may be at risk. The increase in shrublands following historical grazing and higher invasion in the grazed site suggests grazing effects. However, widespread shrublands across the study area tempered conclusions. Study limitations included information gaps, challenges detecting multiple variables and impediments to statistical analysis, given inherited historical conditions. We delimited areas with restoration potential based on spatial analysis, and discussed management response when grazing effects are obscured by a lack of details about the past.