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Measurement and Modelling of Mountain Pine Beetle Impacts on the Annual Forest Water Balance
Burles, K.A.
Aerial overview surveys indicated that in 2004 mountain pine beetle (MPB) infestations in the Southern Interior Region (SIR) of British Columbia covered approximately 4.2 million ha. A 1.5 fold expansion is expected in 2005. Stand characteristics of affected SIR watersheds have been or will be significantly altered due to the natural impact and extent of MPB incursion and the corresponding forest management operations. The post-beetle landscape of these watersheds will be an assemblage of cover types including, for example, clear-cut areas and stands of unaffected and affected juvenile lodgepole pine, selective cut mature mixed species, and mature lodgepole pine stands that have suffered varying degrees of MPB related mortality and defoliation. In addition, regeneration of harvested areas will result in a landscape comprised of a mosaic of juvenile stands of varying ages. Forests play a vital role in the terrestrial hydrologic cycle by partitioning water into different stores and fluxes such as canopy interception loss, snow melt, transpiration, and soil moisture storage. Thus, changes to the composition of forests as a result of MPB and associated harvest activities will have an impact on the magnitudes of hydrologic variables at different spatiotemporal scales. Although generalizations can be made regarding the impact insect infestations and harvesting practices may have on the hydrology of the SIR landscape, many such impacts are likely to be specific to the affected tree species, the management response, and the climatology, pedology and geology of the area. In addition to location specific variability, little is known about the hydrological effects of partial versus complete stand mortality or of the time to reach hydrologic recovery in these areas once regeneration begins. Thus, a detailed study that is specific to different MPB and related management scenarios is required if the impact on the hydrology of the SIR is to be determined. The proposed research will examine how different stands affected by MBP infestations, as well as management practices, such as clear-cutting, understory retention, and juvenile stand management affect the stand water balance. The proposed research addresses three of the research priorities outlined by Hélie et al. (2005): i) MPB impacts on soil moisture storage (Priority 1); ii) the impacts on precipitation/interception loss (Priority 4), and iii) the impacts on evapotranspiration loss (Priority 5). The proposed research will also support the calibration of forest hydrology models that predicatively link changes in hydrologic processes. The research site to be used during this study will be located at Mayson Lake on the Thompson Plateau north of Kamloops where widespread stand losses are anticipated over the next few years and salvage harvesting is underway. It is also the site of a long-term snow hydrology research program. Evaporation from forested environments is comprised of canopy interception loss, transpiration, litter layer interception loss, and direct evaporation from the soil matrix. Canopy interception loss, IC, the interception and subsequent sublimation and evaporation of precipitation by vegetation canopies, represents an important and sometimes the dominant component of the water balance of vegetated environments accounting for approximately 25 ? 30 % of gross precipitation input to mature, undisturbed coniferous forest communities (Dunne and Leopold, 1978; Thurow et al., 1987; Carlyle-Moses, 2004; Winkler et al., 2005). Rain and snow that is not intercepted and subsequently lost from the canopy is partitioned into one of two understory precipitation (PU) inputs: throughfall (TF) and stemflow (SF). Throughfall is the portion of PU that reaches the forest floor by passing directly through gaps in the canopy or as canopy drip, while SF represents the portion of PU that flows down the boles of trees. Although TF typically accounts for 90 % or more of PU in coniferous envir ...
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Abstract - Preliminary Investigation of ...
Abstract - Water Storage Capacities ...
Abstract - Magnitude and Variability ...

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