UBC Theses and Dissertations
Aspects of needle morphology, biomass allocation and foliar nutrient composition in a young fertilized stand of repressed lodgepole pine Keane, Michael Gerard
The dramatic decline in stand productivity associated with very high stand densities in naturally regenerated post-fire interior lodgepole pine (Pinus contorta var. latifolia) stands is called "repression". The reasons for it are unknown. Biomass allocation, needle morphology and foliar nutrition associated with repression were studied in a 20-year-old stand on plots at five densities ranging from 3,500 to 109,000 sph and fertilized at 0, 100 and 200 kg N ha⁻¹ with ammonium nitrate. At higher stand densities, specific leaf area increased while leaf area index declined and light intensities increased below the canopy. As stand density increased from 5000 sph to 90,000 sph, the above-ground biomass decreased from 61 t ha⁻¹ to 16 t ha⁻¹, the proportion allocated to the stem increased from 58% to 78% and the leaf area/sapwood area decreased from 0.3 to 0.13 m² cm⁻². Mean earlywood percentage decreased from 62% to 8% in codominants at 6,500 and 109,000 sph respectively. Although nitrogen deficiency was evident in all stand densities, there were no significant differences between vigorous and repressed stands for the various macro- (N, P, K, S) or micro-nutrients (Cu, Fe, 'active' Fe) examined. It is hypothesized that the decreased proportion of earlywood in repressed trees causes a reduction in stem conductivity leading to the reported drop in the leaf area/sapwood area ratio. The resulting decrease in the photosynthetic/respiratory surface area ratio in repressed stands may lead to their reduced productivity.
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