Increase in Number of Dominant Plants and Dominance-Classes on a Grassland in the Northern Chihuahuan Desert

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Abstract
Between 1915 and 1932, 104 permanent 1 .times. 1-m quadrats were established on grasslands of the Jornada Experimental Range in southern New Mexico. Primary- and secondary-dominant species were determined from the first quadrat records and each quadrat was reevaluated in 1981 to determine current dominants. The first records showed that 13 species of perennial grasses occupied all primary- and secondary-dominant positions on all quadrats. In 1981, there were 12 perennial grass species as primary- or secondary-dominants. Six shrub species occurred as primary- or secondary-dominants on 47% of the quadrat sites in 1981. Dominance-classes, i.e., single-species dominance or two-species dominant combinations, increased from 24 to 43. Thus, vegetation on this range has become more diverse and this diversity must be considered in grazing management.