Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/1995
Publication Date: N/A
Interpretive Summary: From our previous studies we saw that the spatial interaction of nutrients, plants and microorganisms were important in describing ecosystem functioning in the shrub-steppe. From this we developed a geostatistical procedure which combined the effects of all measured variables on the ecosystem. Thus we could determine the importance of a resource and it's spatial relationship to other resources. This new technique will be of value in assessing landscape level processes.
Technical Abstract: Geostatistics are often calculated for a single variable at a time, even though many natural phenomena are a function of several parameters. The objective of this work was to demonstrate a nonparametric approach for assessing the spatial characteristics of multiple-parameter phenomena. Specifically, we analyzed the spatial characteristics of resource islands in the soil under Artemisia tridentata (Nutt), a dominant shrub in the intermountain western United States. For our example, we defined resource islands as a function of six soil variables representing pools of soil resources, populations of microorganisms, and soil microbial physiological parameters. By collectively evaluating the indicator transformations of these individual variables, we created a new data set, termed a multiple-variable indicator transform or MVIT. Alternate MVITs were obtained by varying the selection criteria. Each MVIT was analyzed with variography, to characterize spatial continuity, and with indicator kriging, to predict the combined probability of their occurrence at unsampled locations in the landscape. Simple graphical analysis and variography demonstrated spatial dependence for all individual soil variables. Analysis also showed that ensembles of variables were not randomly distributed, but rather were correlated systematically within the landscape. Maps derived from ordinary kriging of MVITs suggested that the combined probabilities for encountering zones of above-median resources were greatest near A. tridentata. As the selection criteria for defining a resource island became more stringent, the area of the resource island decreased.