Associations of annual plants and shrubs in the northern Chihuahuan Desert

Title	Associations of annual plants and shrubs in the northern Chihuahuan Desert
Publication Type	Thesis
Year of Publication	1991
Authors	Lightfoot KS
Number of Pages	75
Date Published	1991
University	New Mexico State University
City	Las Cruces, New Mexico
Thesis Type	M.S. Thesispp
Accession Number	JRN00135
Call Number	00649
Keywords	annual plant, distribution, annual plant, shrub association, dissertation, dissertations, shub, annual plant, theses, thesis
Abstract	The Chihuahuan Desert in North America consists of semi-arid grassland and shrubland communities. Dominant shrubs in the northern part of the Chihuahuan Desert include Prosopis glandulosa, Larrea tridentata, and Flourensia cernua. The objectives of this research were to examine associations of winter and summer annual plants with three dominant shrub species (Larrea tridentata, Prosopis glandulosa, and Flourensia cernua) and to examine differences between patterns of C₃ and C₄ annual plants. Do annuals tend to be associated with shrubs or are they found more frequently in intershrub spaces? Do winter annuals have stronger associations with shrubs than summer annuals? Is there a pattern of species-specific associations between annuals and the three dominant shrub species in areas where all three shrubs co-occur, controlling for soil differences? If so, do the same patterns of annual-shrub associations exist in areas where single shrub species dominate on potentially different soils? Does a pattern emerge on different soils, indicating that soils rather than properties of the shrubs more strongly determine associations? Is one shrub species "preferred" by any annual plant species over other shrubs, or is the microhabitat provided by any shrub equivalent in accounting for patterns? I sampled annual plants under and near shrubs, on plots codominated by the three shrub species and on plots dominated by single shrub species. I then used statistical methods to test for associations between annual plants and shrubs. There were significant differences in annual species composition among single shrub plots, and among quadrats differing in position relative to shrub canopy. There were no significant differences in annual plant species composition among the three shrub species on mixed shrub plots. Soil or other micro-environmental site differences, other than the species of shrub, must be responsible for differences in annual plant communities.