Historical Land Clearing in the Fraser Lowland of British Columbia and Washington State: II. Effects on Soil Variability

Abstract

The purpose of this study was to determine the effects of land clearing and consequent management differences on soil variability. The study is unique in its examination of temporal changes in soil properties based on the interpretation of historical land use changes in an international boundary region. Ten samples were collected from the top 0.2 m of the surface horizon on each of 60 plots by stratified random sampling using a 900-m2 grid. Plots were chosen in duplicate and represent the two countries (Canada and the USA), the three parent materials (alluvium, glacial outwash, and glacial marine drift), and the five land clearing age groups (cleared between 1943 and 1955, 1955 and 1966, 1966 and 1976, 1976 and 1983, and not cleared, i.e., woodland). The samples were analyzed for pH in H2O and CaCl2, Ca, Mg, K, P, organic matter (OM), and N. Variability of the soils formed in their respective parent materials is in the order alluvium ≤ outwash ≤ glacial marine. In comparison to coefficients of variation reported in the literature, those in this study are lower for OM and N, and comparable for bulk density, pH, Ca, Mg, K, and P. No pattern with time occurs among the four cultivated land clearing groups, nor is there a time trend by land use for any of the parent materials. The variability of woodland soils ≥ variability of cultivated soils. Variability differences due to country are also mixed in spite of management differences. Commonly 50 to 80% of the variation within all cultivated soils combined is within any individual 0.09-ha cultivated plot.