Divergent evolution and the spatial structure of soil landscape variability

The spatial structure of soil variability at the landscape scale was examin ed on adjacent geomorphic surfaces dating from 80 to 200 ka in eastern Nort h Carolina. The purpose was to determine whether there is evidence at broad er scales (distances of 10(2)-10(4) m) fur the divergent evolution observed in the field at very detailed scales (distances of 10(0)-10(2) m). The sta te probability function (SPF), which measures spatial dependence for catego rical environmental data along a transect, was applied to soil series mappe d at a 1:24,000 scale. The older Talbot Terrace and younger Pamlico Terrace surfaces showed distinctly different patterns of spatial variability. The range of spatial dependence was shorter on the older surface (about 200 vs. 300 m), and the SPF was higher at any given distance, indicating more vari ability. The SPF for the Pamlico surface also indicates a periodicity relat ed to fluvial dissection of the landscape, which is not readily detectable on the Talbot transect despite its greater degree of dissection. The result s confirm earlier field studies which suggest that pedogenesis is marked by divergence, whereby differences in initial conditions or local perturbatio ns persist and increase to produce a more variable soil cover. (C) 2001 Els evier Science B.V, All rights reserved.