Date of Award:

5-1-1974

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Biology

Committee Chair(s)

James A. MacMahon

Committee

James A. MacMahon

Committee

Keith L. Dixon

Committee

Neil West

Abstract

An enumeration of a 0.99 ha plot of Southwestern Desertscrub, Lower Sonoran, paloverde-sahuaro perennial vegetation in Arizona contained 1690 individuals in 13 species providing a coverage of 21 percent of the area. Analysis of the enumeration plot by Importance Values (relative frequency + relative density + relative cover dominance) shows that Larrea divaricata and Ambrosia dumosa are the co-dominants in the community, constituting 60 percent of all individuals present. The area was sampled in the field by three methods: point-quarter, line-intercept and quadrats. Point-quarter (90 points) estimates dominance more accurately (10-15 percent error) than density (21 percent). The line-intercept method using twenty-one 90 m transects estimates cover within 17 percent of the actual but does not adequately estimate relative density. Random or stratified random sampling regimes of forty 10 x 10 m quadrats give accurate estimates of density and dominance within 15 percent of the actual. The point-quarter and line-intercept methods were duplicated by sampling a laboratory map of the enumerated area; field samples resulted in more accurate estimates. Aerial photography (scale = 1:1000) yielded an average 30 percent underestimate of density and dominance which can be attributed in part to the dispersion of smaller shrubs under large species. Pattern analysis by plotless methods of six species suggests a significant overall contagion with regularity within clumps.

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