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Predicting tree growth and beetle susceptibility after fire

We are creating tools to inform post-fire decisions that predict post-fire growth rates and mortality levels due to fire alone or fire+beetle for ponderosa pine (PP) and Douglas-fir (DF). The models in the tools will account for tree size, fire injury, site productivity, changes in competition, and beetle pressure. The project will also validate and update current FVS post-fire growth predictions.

This project determines (1) whether fire-injured PP and DF trees ever truly recover and (2) to what degree this influences forest susceptibility to beetle attacks compared to unburned areas. Previous studies show that trees with low pre-fire growth rates are more likely to die, both from fire and from other causes such as drought, beetles, and competition. However, post-fire growth has not been examined nor related to fire injury and competition. Thus, this project will create a tool to forecast mortality and growth with and without beetles over longer post-fire windows (i.e., 8-15 years) than are currently accounted for and will validate Forest Vegetation Simulator (FVS) predictions. The growth and beetle susceptibility tools developed could be used for informing salvage logging operations, non-salvage silviculture prescriptions, and wildlife habitat modeling (e.g., snag recruitment).

In order to develop a tool that will address (1) whether fire-injured PP and DF recover, and (2) to what degree this influences forest susceptibility to beetle attacks compared to unburned areas, we are using a two-pronged approach: a fine-scale assessment of tree growth and beetle susceptibility paired with a coarse-scale assessment of beetle activity between burned and unburned areas. Fine-scale Assessment: We have identified previous post-fire studies that include permanent, fixed area plots where trees were individually tagged immediately post-fire, tree-level fire injury was assessed, and where time since fire has been at least 8 years. Fixed area plots allow calculation of a competition index. We are revisiting these plots and collecting tree cores to quantify pre- and post-fire growth response and resin duct defenses. At each plot we re-measure vegetation (trees ≥ 4 in DBH) to relate growth patterns to competition (e.g., density, basal area, SDI), DBH, site potential productivity (e.g., site index, plant association, AET), and fire injury (e.g., crown scorch, cambium killed). We also establish fixed-area plots in nearby unburned areas and core trees to function as a control. Coarse-scale Assessment: Using the same fires from our fine-scale assessment, we are comparing beetle activity inside fire perimeters to adjacent unburned areas to determine whether attack severity varies, and relate those patterns to fire injury, growth rate, and resin duct defenses using ADS data. FVS Validation: The last phase of the project will validate the FVS growth predictions.

Photo: Approximately 10 years after a wildfire in western Montana.

Approximately 10 years after a wildfire in western Montana.

Modified: Oct 10, 2019

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