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Quantitative classification of soil nutrient regimes of some mesothermal Douglas-fir ecosystems Kabzems, Richard Darwin


Previous attempts to classify nutrient regimes of forest soil have been qualitative evaluations utilizing vegetation and/or physiographic site characteristics, morphological soil properties, and parent material. The major objective of this study was to describe and classify the soil nutrient regimes (SNR) of some Pseudotsuga menziesii ecosystems on southern Vancouver Island, British Columbia. The order of increasing variability for forest floor properties was pH(H₂0) <TC <TN <TS <TP <exMg <exCa <exK <exMn <minN. The order of increasing variability for mineral soil properties was pH(H₂0)=pH(CaC1₂) <TN <TC <exP = exMg <S0₄ <minN = exK <exCa <exMn. Consistent trends in soil property variability along gradients of soil moisture or nutrient availability or between parent material lithologies were not apparent. Multivariate analysis of understory vegetation and indicator plant analysis suggested a major trend in variation corresponding to a complex environmental gradient related to increased availability of soil moisture and nutrients. The arrangement of study plots along the gradient showed groupings which corresponded to both the calculated soil water deficit and inferred soil nutrient regime. One multivariate axis accounted for most of the variation of soil properties between study plots. The mineral soil and forest floor plus mineral soil quantities of minN, TN, exCa and exMg significantly increased along the nutrient gradient. Ordinations of mineral soil and forest floor plus mineral soil properties arranged most plots according to the moisture-nutrient gradient. Discriminant analysis of the soil properties selected linear combinations of properties which separated sites, parent material lithologies, soil moisture regime classes and SNR classes. Cluster analysis confirmed that minN and exMg of the forest floor plus mineral soil best separated SNR classes. Multivariate summaries of variation in understory vegetation and foliar nutrients were highly correlated to the soil properties which best separated SNR classes. The increasing quantities of these nutrients corresponded to increases in site index for the study sites. It was concluded that significant differences in N, Ca, and Mg availability existed between SNR classes for the study sites. These differences in nutrient availability corresponded to changes in understory vegetation, foliar nutrient status and site index for the study sites. Using forest floor plus mineral soil quantities of minN and exMg, a multivariate classification of the four SNR classes recognized in this study was proposed.

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