Hydrological and ecological assessments of a discrete range site on the Southern High Plain

Plant community types within a range site classification (loamy blue grama (Bouteloua gracilis)/buffalograss (Buchloe dactyloides)) and their attributes (richness, diversity, and evenness) were investigated so that species abundance relationships and hydrological assessments (infiltrability, runoff, and sediment production) could be evaluated. This study consists of 2 parts: (1) model infiltrability and sediment production with a set of predictor variables on 5 plant community types within a discrete loamy range site, and (2) identify possible relationships between successional stages, plant species diversity, evenness, and environmental variables for the 5 plant community types.;From a thermodynamic perspective: a plant community associated with instability is characteristic of increasing or high levels of entropy--climax plant communities can be viewed as having less entropy. My hypothesis considered that since plant succession is a time-dependent integration of all ecological processes at a particular site, the subsequent plant community and compositional changes within it would also reflect certain hydrological patterns.;A portable single nozzle rainfall simulator was used to determine infiltrability, runoff, and sediment production from blue grama, blue grama/buffalograss, buffalograss, broom snakeweed (Gutierrezia sarothrae), and annual threeawn (Aristida oligantha)/Texas tumblegrass (Schedonnardus paniculatus) plant community types in 1988 and 1989.;The results indicated that there were no significant differences along an infiltration curve (5 to 50 minutes) for the blue grama and broom snakeweed community types. Blue grama/buffalograss stands occurred midway on the curve with buffalograss and annual threeawn/Texas tumblegrass stands exhibiting significantly lower infiltrability. Important predictor variables of infiltrability and sediment production were biomass, phytomass, plant community type, successional stage, canopy cover, root biomass, and soil texture. Plant community type was important in modelling infiltrability; whereas, successional stages were not. Plant community types and successional stages were both important in predicting total sediment yield.;Detrended Correspondence Analysis and Two-way Indicator Analysis identified seral relationships, and patterns of plant species diversity and evenness among the 5 plant community types. Ordinations based on diversity and evenness values were more interpretable from a successional viewpoint than ordinations based on cover data. Diversity and evenness was highest in the annual threeawn/Texas tumblegrass stands and lowest in the climax blue grama stands. Environmental variables were correlated with the ordination axes.