Graduate Thesis Or Dissertation


Restoring Ponderosa Pine: Understanding Individual Tree Defenses, Disturbance Responses, and Resilience Public Deposited

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  • The aim of this research was to provide forest managers and researchers with a better understanding of individual tree defenses and tree responses to disturbances, within a Collaborative Forest Landscape Restoration Program area. Forest restoration often aims to increase stand-level resistance to uncharacteristic changes, and stand-level resistance begins with tree-level defenses. Little research exists on individual tree defenses and growth responses in a landscape undergoing restoration treatments. I begin by exploring models and frameworks for understanding resin production, which is the main defense mechanism of ponderosa pine trees (Pinus ponderosa Dougl. ex Laws.). Past studies have suggested that resin flow increases with tree growth, resin duct size, and total duct area, but my research suggests that there are thresholds to these relationships that vary by situation. Forest managers should not expect a linear increase in resin flow as tree growth increases; instead, increasing the growth of small and slow-growing trees may have the greatest impact on resin flow. After fire, trees burned at higher severities show greater increases in total duct area per unit of growth. However, high-severity fire also decreases tree growth, especially in larger trees. Use of higher severity prescribed fire, or use of wildfire for resource objectives, may come with trade-offs between tree growth and tree defenses. Resin ducts are highly resistant and resilient to impacts from fire, while tree growth tends to decrease after fire. Tree growth responses to fire are influenced by past investments in defenses relative to growth. Short-term decreases in growth after fire may be balanced out by potentially higher defenses against future disturbances. Forests face many potential threats from changes in climate and disturbance regimes. Designing restoration treatments to increase tree defenses may be beneficial to forest health and resistance to transformations, even if increases in defenses sometimes come at the expense of short-term tree growth. 
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