Here, we propose to use almost entirely existing stand spatial data and snow-melt data to model early season water availability in mountain pine beetle (MPB) affected stands. As a result of the current MPB infestation the majority of mature lodgepole pine (Pinus contorta Dougl) in MS zone stands has been or will be killed by the beetle. The resultant canopy loss and changes in the spatial characteristics of these forests is likely to have an influence on the volume and timing of snow melt and, consequently, on water availability within these stands (Helie et al 2005). Previous snow melt studies have found that a decrease in canopy closure often results in an increase in snow accumulation and in ablation rates (Davis et al. 1997; Emmanuel Sicart et al. 2003; Winkler et al, 2005 Winkler and Moore, 2006). We plan to model changes in stand attributes post-MPB and the consequent changes in early growing season water availability contributed by snow melt in 3 MS zone stands. Through previous research funding, these stands aged 20, 80 and 140 yrs, were stem mapped and have up to 7 yrs of snow measurements. If funded, the information gathered from this project will improve our understanding of the impact of the MPB on early growing season site hydrology, water availability, and site productivity.
To model snow ablation in the three stands we intend to use a model that is a combination of: wind speed, temperature, incident radiation, canopy view factor, and a spatial component (proximity index) that relates snow melt volume and snow pack disappearance rates to the size, species, and distance of adjacent trees. Incident radiation has been measured using hemispherical photographs and where these are unavailable estimates of incident radiation on the snow surface will be predicted using the spatially explicit light model described in Canham et al.(2004). This light model predicts incident radiation at a given location in a stand and is analogous to the methods used to estimate incident radiation from hemispherical photographs. Hardy et al.(2004) found that hemispherical photos can be used to specify the distribution of solar flux under a canopy. The proximity index will be parameterized using the existing snow melt and tree spatial data. The index is an adaptation of a competition index developed by Canham et al. (2004).
It is also our intention to use the snow ablation model in conjunction with simulation output from SORTIE-ND to forecast the ongoing affects of MPB on ablation rates to determine the effects of infilling and re-growth for these stands. SORTIE-ND is a resource-mediated, spatially explicit, mixed-species forest model that makes population dynamic forecasts for juvenile and adult trees. It has a flexible user-interface that allows the user to incorporate a wide range of silvicultural strategies or even episodic events such as the current MPB infestation. To better understand the impacts of changes in site hydrology on productivity we also plan to test for correlations between snow melt volume and duration and tree radial increment.
Blenner-Hassett, Trevor. 2009. Predicting changes in early growing season water availability contributed as snowmelt following mountain pine beetle attack. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2009MR310
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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