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The relationship between foliar and soil chemistry, growth parameters, and variable height growth in advance regeneration of amabilis fir Husted, Lynn Diane

Abstract

Many stands of advance amabilis fir regeneration near Courtenay, B.C. exhibit declining height growth after an initially good release response following logging of the overstory. The objectives of this thesis were to investigate the relationship of nutrition, particularly nitrogen, to this height growth pattern on one site. Foliage from trees representing the range of height growth on the site was collected twice monthly from May to September for chemical analysis. In September, samples from the major rooting zone (H horizon) of well and poorly grown tree microsites were also collected for chemical analysis. Measurements of non-nutritional factors (age and height at release, aboveground competition, diameter growth) were taken to assess the contribution of these variables to height growth. Microsite differences in site moisture were not measured due to lack of time and equipment. However, the foliar chemistry of trees growing on well-drained (mesic) and rapidly-drained (xeric) sites was compared to estimate the effect of microsite differences. Height growth was significantly related to foliar chemistry, particularly nitrogen in multiple regression equations. This relationship was better in most cases with summer rather than fall foliar chemistry measurements. There were significant differences in nitrogen, carbon: nitrogen ratios, magnesium and calcium between the humus of well and poorly grown tree microsites. A proposed scenario for the decline in height growth following initially good relase growth was proposed. None of the non-nutritional factors measured related significantly to height growth after release. Differences in crown size at release and microsite water availability are the most likely factors accounting for differences in the rate of height growth decline other than nutrition.

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