Graduate Thesis Or Dissertation
 

Green-tree retention and ectomycorrhiza legacies : the spatial influences of retention trees on mycorrhiza community structure and diversity

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  • These studies are part of the Demonstration of Ecosystem Management Options (DEMO) study, a program researching the effects of different levels and patterns of green-tree retention on ecological, economic, and social phenomena. We restricted our studies to the 15% basal area, evenly dispersed retention treatment. Our objectives were, first, to quantify the change in ectomycorrhiza (EM) type richness after treatment. Second, to determine if changes in EM type richness depended on proximity to retention trees by quantifying EM type richness and root density at four distance classes from retention trees. Third, to determine the relationship between photosynthetic potential of retention trees (measured by cross-sectional sapwood area), root density, and EM type richness. Finally, to determine the effects of retention-tree productivity, root density, and distance from host tree on EM community structure. Three sites (blocks) of the DEMO study were used: Hamilton Buttes, Dog Prairie, and Watson Falls. Pretreatment samples were taken between one and three years before thinning. Post-treatment samples were collected within two years of the thinning. Ectomycorrhizae were sampled using 5.5 cm diameter by 15 cm deep soil cores and identified by morphotyping techniques. We found a significant reduction in EM type richness as a result of the thinning treatment. Within the dripline of retention trees, however, there was no significant decline in the number of EM types. In areas removed from trees, there was up to a 50% decline in the mean number of EM types per soil core. Samples within the dripline and at the edge of the dripline (host-tree samples) had no significant differences in EM type richness or community structure when compared to each other. When host-tree samples were compared to soil cores taken just outside the dripline and in open areas, significantly lower EM type richness was detected, as was a shift in overall community structure. Ectomycorrhiza type richness was found to be significantly and positively correlated with fine-root tip density. Sapwood area of retention trees had no significant correlations with root density, EM type richness, or community structure. The community structure of EM, in terms of relative abundance, most closely followed the log-normal distribution. In the outside dripline soil cores, there were very few rare types observed, suggesting that the probability of an EM type being lost was linked with its pre-disturbance abundance and the loss of the host tree. Cenococcum geophilum was the most abundant EM type, accounting for 18.7% of EM tips, and occurring in nearly all samples. Retention trees serve as important refugia for EM. This biological legacy from the pre-disturbance stand may be important for recolonization of EM onto new seedlings. For those EM that are lost from these treatment units, early recolonization may occur from the spore bank or wind dispersal. Over time, hypogeous fruiting species and those adapted to conditions in a mature forest may re-colonize from neighboring forest stands, provided the distance to the edge of reserve areas is not too great for effective spore dispersal.
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