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Functional relationships between salal understory and forest overstory Vales, David Joseph


Abundance of salal (Gaultheria shall on Pursh) and its relationship to forest overstory were studied in immature forest stands on Vancouver Island having some topographical characteristics of deer winter ranges. Plots sampled over a range of stocking levels indicated that salal density was strongly related to single forest stand characteristics (r²= 0.92-0.94) but predictive equations differed between plant associations. Most equations predicting salal biomass or cover did not differ between plant associations. Equations calculated from data from single stands accounted for more o the variation in salal abundance (r² = 0.73-0.97) than equations developed from data from several stands (r² = 0.39-0.92). Mean salal shoot height was greatest under overstory cover of 65 to 80%. Transmission of global, direct, diffuse, and diffuse photosynthetically active solar radiation through forest canopies was studied on 12 plots during sunny days in summer The proportions of radiation transmitted were a function of forest stand characteristics and differed among radiation components. The relationship between the proportion of diffuse radiation transmitted and stand characteristics differed among stand structures. When direct beam radiation was scattered by open crowns of short trees and crowns extended below the height of radiation sensors, diffuse radiation below the canopy was higher than outside. The extent to which different forest stand characteristics predict transmission and follow Beer's law were explored. Sum of tree diameters and Reineke's stand density index predict transmission of global (i² = 0.80-0.95) and direct radiation (i² = 0.70-0.98) best. Overstory cover predicts transmission of diffuse radiation best (i² = 0.74) when there is extensive inter-plot variation and bases of tree crowns are above sensors. Forest stand characteristics obtained by different sampling methods gave different predictabilities of the components transmitted. Differences were found between hemispherical photograph estimates of diffuse radiation transmitted and measured transmission of diffuse and diffuse photosynthetically active radiation. Photographic estimates of direct radiation transmitted differed from measured transmission of direct radiation. The relationships of salal characteristics to transmission of solar radiation components were examined. Salal density, basal area, foliar productivity, biomass, and cover all increased asymptotically with increasing transmission. The growth of-salal was more closely related to transmission of direct radiation (i² = 0.65-0.99) than to global, diffuse, or diffuse photosynthetically active radiation. The rate at which salal abundance plateaued was fastest for transmission of direct radiation. Salal shoot height and basal diameter were largest for low to moderate proportions of radiation transmitted. The lowest and greatest proportions transmitted seemed to adversely affect salal shoot height and diameter. Shoot productivity increased asymptotically with increased transmission. Salal maximum abundance and shoot size are regulated by the amount of direct solar radiation received at a site and probably by an interaction with a site's moisture regime.

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