Ettema & Wardle 2002

Ettema CH, Wardle DA. 2002. Spatial soil ecology. Trends in Ecology & Evolution 17: 177-183.

These authors review the growing use of explicit geospatial analysis techniques in soil biology. As this is a TREE article, there are several helpful boxes that explain fundamentals of geospatial analysis such as the terminology and key case studies. This is also a review article, so there are descriptions of various previous studies that include evidence useful in answering the questions set out in this paper. These questions are 1) What are the scales, patterns and causes of spatial variability in soil organism distributions? 2) What are the implications of spatial variability for the structure and function of soil communities? 3) How do spatial properties of the soil biota influence plant communities?

Regarding question 1, the scales and patterns of spatial variability in soil organisms range from 10s and 100s of metres down to millimetres. Studies of soil microbes including methanogenic Archaea have included soil corers of 1mm diameter (based on a hollow needle) and aggregations of organisms separated by distances of 2 to 4mm.

Soil communities and their influence on plant communities were found to be highly non-uniform, and show predictable though complex spatial patterns. However, while much was made of the role of individual plants (especially trees) to structure the soils around them and create spatial patterns of microbes and invertebrates on the same scale as the trees themselves are distributed, very little was made of the role that small-scale aggregations play in structuring larger patterns. This is surprising, given the highly biased view of soil processes in this paper and more generally in the soil science literature: soil is viewed as something that exists primarily to support plants, rather than a system of its own independent importance. That is the impression I have gotten, at least.

This paper is a very useful overview of geospatial analysis, and the reference list includes a number of similarly useful papers. In particular, further exploration of the statistics of semivariance patterns seems useful.