Soil Heterogeneity Changes During Forest Succession: Test of a Model Using Univariate and Geostatistics

Abstract

We sampled forest stands in upland forests of the Southeastern US along a chronosequence of a replicated successional forest sere (1, 6, 10, 25, and 80 years) to elucidate the temporal changes in soil spatial heterogeneity. Samples were collected from loblolly pine plantations representing reorganization through aggradation phases of succession, and from one set of oak-hickory stands to signify the steady-state phase of the model. These trends are characterized and compared to a conceptual model of pattern dynamics. Variability in soil properties (NO3, NH4, pH, Total N, Total C) and forest floor litter at scales relevant to individual plants was quantified using univariate and geostatistical procedures. Global variation (using both coefficient of variation and standard deviation), patch size and proportion of spatially structured variation were examined for individual variables at each successional stage. These patterns were also averaged to produce a generalized model of spatial heterogeneity change during succession. Individual variables often showed differing patterns. However, when patterns from individual variables were averaged, overall patterns emerged. Early in succession global variability was largest and patch sizes were smallest. As succession progressed, trends in the data showed that global variability decreased and patch sizes increased to the middle stage of succession. Both of these trends fit our conceptual model of pattern dynamics. However, the slopes in these trends were not significant at alpha=0.05.