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

Abstract

The purpose of this study was to determine the effects of land clearing and consequent management differences on soil genesis. 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 on 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. The principal anthropogenic effects resulting from land clearing on soil genesis in the horizons sampled are the following: (i) pH increases dramatically on the soils formed in all three parent materials from initial levels in woodland. (ii) The levels of cations are determined by the fertility of the soil at the time of clearing. Soils formed in outwash and glacial marine deposits have low fertility under woodland and cation levels increase 2 to 15 times after cultivation. Cation levels decrease from initially high levels on woodland soils formed in alluvium. (iii) Cultivation results in losses of OM of 20% after 35 yr on all soils. (iv) Nitrogen levels are inconsistent. (v) Carbon/N ratio narrows on all soils to an apparent steady state of about 12:1. (vi) Bulk density increases by 25 to 58%. Contribution from the Dep. of Soil Science, Univ. of British Columbia.