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Globally, the most bioavailable elements (Ca, Mg, and K) are amongst the most abundant in the crust, but N is more abundant than predicted • Bioavailability was controlled by soil pH, organic matter content, texture, plant cover, and climate, and altered by global change • Elements were highly spatially correlated (coupled), and coupling was predictable by the atomic properties of elements, particularly mass

The author has granted a non exclusive license allowing Library and Archives Canada to reproduce, publish, archive, preserve, conserve, communicate to the public by telecommunication or on the Internet, loan, distrbute and sell theses worldwide, for commercial or non commercial purposes, in microform, paper, electronic and/or any other formats. AVIS: L'auteur a accorde une licence non exclusive permettant a la Bibliotheque et Archives Canada de reproduire, publier, archiver, sauvegarder, conserver, transmettre au public par telecommunication ou par I'lnternet, preter, distribuer et vendre des theses partout dans le monde, a des fins commerciales ou autres, sur support microforme, papier, electronique et/ou autres formats. Bien que ces formulaires aient inclus dans la pagination, il n'y aura aucun contenu manquant. Canada Dendroctonus ponderosae (Hopkins) or mountain pine beetle is a native bark beetle (Coleoptera: Curculionidae: Scolytinae) that feeds on more than 20 species of pine in western North America. In British Columbia, its principal host is lodgepole pine (Pinus contorta var. latifolia Engelmann). As a "primary" bark beetle, D. ponderosae kills its host at epidemic stages, exerting profound landscape-level mortality. As of 2012, D. ponderosae has caused the loss of 726 million cubic meters of timber, covering an area of 17.5 million hectares of mature pine forest in British Columbia and Alberta. Small diameter hosts are not suitable for D. ponderosae, however, creating a niche for the "secondary" bark beetles, including Ips pini (Say), Pseudips mexicanus (Hopkins), and Orthotomicus latidens (LeConte). At the post-epidemic stage of D. ponderosae, we found the rate of new mortality was approximately 4%, which 1% of the mortality was associated with a complex of secondary bark beetles, and not D. ponderosae, as the principal mortality agent in those stands. This finding suggests that at high population densities, secondary bark beetles are potential mortality agents of residual pines, sustaining the apparent outbreak of D. ponderosae by killing smaller diameter trees, with the highest rate of mortality among younger stands.

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Soils contain microbial inhabitants that differ in sensitivity to anthropogenic modification. Soil reclamation relies on monitoring these communities to evaluate ecosystem functions recovery post-disturbance. DNA metabarcoding and soil enzyme assays provide information about microbial functional guilds and organic matter decomposition activities respectively. However bacterial communities, fungal communities, and enzyme activities may not be equally informative for monitoring reclaimed soils. We compared effects of disturbance regimes applied to forest soils on fungal community composition, bacterial community composition, and potential hydrolase activities (N-acetyl-β-D-glucosaminidase, acid phosphatase, and cellobiohydrolase) at two times (14 days and 5 months post-disturbance) and depths (LFH versus mineral soil). Using disturbance versus control comparisons allowed us to identify genus-level disturbance-indicators and shifts in hydrolase activity levels. We observed declines in disturbed LFH fungal biomass (ergosterol) and declines in ectomycorrhizal fungi abundance across all disturbed samples, which prompted us to consider necromass-induced (fungal, root) saprotroph increases as disturbance indicators. Fungal community composition strongly shifted away from ecotmycorrhizal dominance to saprotroph dominance (i.e. increased Mortierella, and Umbelopsis) in disturbed plots at 5 months, while bacterial community composition did not shift to distinguish control plots from disturbed ones at either sampling time. Soil potential hydrolase data mainly indicated that mixing LFH material into mineral soil increases the measured activity levels compared to control and replaced mineral soil. Bacterial saprotrophs previously associated with mycelial necromass were detected across multiple regimes as disturbance indicators at 14 days post-disturbance. Our results confirm that ectomycorrhizal fungal genera are sensitive and persistently impacted by soil physical disturbances. Increases in saprotrophic bacterial genera are detectable 14 days pot-disturbance but only a few persist as disturbance indicators after several months. Potential hydrolase activities appear to be most useful for detecting the transfer of decomposition hotspots into mineral soils.