Effects of disturbance on tree level resistance in ponderosa pine trees along the Colorado Front Range
Date
2024
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Abstract
Forest restoration treatments are being implemented across ponderosa pine systems along the Colorado Front Range with goals of reducing risk of catastrophic wildfire, returning forest structure to historical conditions, and increasing ecosystem resilience and resistance in the face of climate change. While there are studies monitoring effects of thinning and wildfires on forest structure across the Front Range, few studies assess the effects of disturbances from wildfires and thinning treatments on tree-level resistance. Here we examined forest stand structure, growth, and defense characteristics in response to treatments and wildfires through the collection of plot level data, tree-level characteristics, and tree cores. We sampled 160 plots in areas that experienced thinning treatments between 2007-2012, were burned by low-severity wildfires (2012 Hewlett Gulch and High Park Fire, 2010 Fourmile Canyon Fire and Dome Fire, 2012 Flagstaff Fire, 2012 Waldo Canyon Fire), or that were untreated and unburned (hereafter "control"). Our findings reveal that tree growth and resin duct size significantly increased following thinning treatments. Relative resin duct area and duct density were significantly higher in trees following wildfire compared to trees that experienced thinning or to those trees within control plots. Control plots exhibited the highest mean basal area and stand density index, coupled with the lowest quadratic mean diameter, indicating high inter-tree competition, which both thinning and low-severity wildfire helped alleviate. Overall, our results highlight the beneficial impacts of both thinning and low-severity wildfire on mature ponderosa pine trees by enhancing their resistance to future disturbance, such as bark beetle outbreaks and drought.