Changes of Vegetation and Diversity in Grasslands along 28 Years of Continuous Grazing in the Semi-Arid Durango Region, North Mexico

Researchers analyzed the effects in floristic composition and vegetation structure in grassland of the Semi-arid region of Durango, Mexico under continuous grazing for 28 years. Researchers carried out quantitative sampling of the vegetation in two cycles, Autumn, 1979 and repeated in Autumn, 2007. Data set obtained for relative density, dominance and frequency of species were analyzed in terms of cycles and sampling sites. Researchers analyzed changes in diversity through Shannon-Wiener's index while for spatial distribution Ward's algorithm and principal component analysis were used. An increase in soil vegetation cover (25.46%) resulted as well as an increase inbiomass (161%) mainly due to the greater precipitation that occurred in 2007 (550 mm) compared to that of 1979 (293.4 mm). However, a decrease of native grass diversity occurred while the African introduced species (Melinis repens) Zizka rose Natal grass increased in dominance from 4-30%. That gave us a major change in the vegetation structure going from Bouteloua bothriochloa association to Melinis heteropogon.