Forest Investment Account (FIA) - Forest Science Program
FIA Project M086035

    Measurement and Modelling of Mountain Pine Beetle Impacts on the Annual Forest Water Balance
Project lead: Carlyle-Moses, Darryl (Thompson Rivers University)
Contributing Authors: Burles, K.A.; Carlyle-Moses, Darryl E.; McGivern, V.J.; Kono, G.; Winkler, Rita D.; Spittlehouse, David L.; Redding, Todd
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
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 environments, including lodgepole pine stands (see Brabender, 2005), SF may represent an important point input since many trees funnel water from their relatively large canopies where it is concentrated at their relatively small bases. Given the quantitative importance of IC and PU fluxes a number of models have been developed to estimate their magnitudes. Commonly reported regression models are limited in their spatiotemporal transferability since stand characteristics and meteorological variables controlling the rate of evaporation of intercepted rainfall are often ignored. The most commonly used conceptual models are the Rutter (1971, 1975) model and the analytical version of this model proposed by Gash (1979) and subsequently modified by Gash et al. (1995) and Valente et al. (1997). Although good agreement between observed and simulated IC and PU fluxes have been found at the plot-scale using the Rutter and Gash models in a variety of environments (e.g., Loustau et al., 1992; Carlyle-Moses and Price, 1999), these models, like their regression model counterparts, are limited in terms of their spatiotemporal transferability since they treat the canopy as a two-dimensional ‘big-leaf’. The modified versions of the Rutter and Gash models scale parameters such as the storage canopy (S) and the during-rainfall evaporation rate from a saturated canopy (E) to the fraction of canopy cover, but no other stand characteristic. Thus, under the current Rutter and Gash model structures spatiotemporal extrapolation would generate similar model parameters, and thus IC and PU estimates, in stands of comparable canopy cover fraction even though other stand characteristics such as leaf area index (LAI), stand volume, and tree density may differ appreciably. Preliminary results from the first field season (2006) suggest that interception loss from the bryophyte dominated floors of mature stands may be greater than that from the canopy. For example, canopy interception loss accounted for 29 and 26 % of the 61 mm of rainfall that fell during the period of early June to early August from a mature stand and a mature stand with MPB infested pines selectively cut, respectively, while interception loss from the bryophyte dominated floor accounted for 33 and 32 % of rainfall. As a result of this finding a more intensive sampling procedure to determine the magnitude and variability of forest floor water stores and fluxes will be established during the second year.


Final Report (0.4Mb)
Abstract (75Kb)
U of W Handout (0.1Mb)
Mayson Lake Presentation (1.8Mb)
Snow Processes on the Thompson Plateau (Presentation) (1.9Mb)
Hydrologic Implications of the MPB (Presentation) (2.2Mb)
Rainfall at Mayson Lake (Presentation) (3.0Mb)
Water Balance (Presentation) (5.6Mb)
CGU Conference Poster (0.3Mb)
Interception Loss (Presentation) (0.7Mb)
Mayson Lake Study ... (LINK Article, Volume 9 Issue 2)

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Updated August 16, 2010 

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