Invasive Lehmann lovegrass (Eragrostis lehmanniana) in Chihuahua, Mexico: Consequences of invasion

Plant community dynamics, including vegetation changes in cover (%), species richness, diversity, evenness and similarity indices were assessed in a bunchgrass type rangeland in central Chihuahua, Mexico over a 20 year period (1985-2005). The goal of this study was to quantify the progressive invasion of Lehmann lovegrass (Eragrostis lehmanniana) from its original source of introduction in the mid-1960's. Vegetation was recorded along 46 permanent transects located and evenly distributed from 3 000 to 6 000 m distance from the original Lehmann lovegrass seed source. Vegetation changes were evaluated by using a pair t-test (P < 0.05) comparison among years. From all species; 15% disappeared, 30% declined, 49% remained unchanged and 6% increased in cover. Most grasses reduced cover over 50%, Bouteloua gracilis appeared in site, and invasive Lehmann lovegrass expanded cover for over 200 times. Six forbs species disappeared and five declined in cover by more than 80%. Two semi-shrubs: Gutierrezia microcephala and Viguiera decurrens disappeared. Seventy percent of shrubs remained unchanged, where Prosopis glandulosa appeared and Nolina texana expanded by 5 times. Species richness (species per transect) decreased from 15 species in 1985 to 6 species in 2005 from 3 000 to 4 500 m from the original seed source. Similarly, plant diversity (Shannon's index) declined from 1985 (from 2 - 3.5 to 1 - 2.5 index value) in 2005. Vegetation changes in the 20 year period affected the abundance of many plant species and community diversity, Lehmann lovegrass exhibited a significant and progressive invasion of this central rangeland of Chihuahua.;Key Words: diversity, evenness, invasive, plant cover, richness, similarity index.