If Long-Term Resistance to a Spruce Beetle Epidemic is Futile, Can Silvicultural Treatments Increase Resilience in Spruce-Fir Forests in the Central Rocky Mountains?

Abstract

Abstract:Within the Central Rocky Mountains, spruce beetle populations have the potential to rapidly transition from endemic to epidemic levels in the spruce-fir (Engelmann spruce and subalpine fir) forest type. Conventional management has focused on creating resistance to spruce beetle outbreaks by manipulating the overstory density and composition. Three silvicultural treatments, single tree selection, group selection, and shelterwood with reserves, were established in a spruce-fir forest in northern Utah with the goals of increasing both resistance and resilience to outbreaks. Resistance and resilience metrics were explicitly defined. Pre-harvest and two post-harvest measurements were used to assess how the different silvicultural treatments influenced the metrics. The shelterwood with reserves was the only treatment to meet both the resistance and resilience criteria. This treatment, while not traditionally used, created a stand structure and composition that will be most resilient to climate induced increases in spruce beetle caused tree mortality. However, there will be a trade-off in composition and structure, especially Engelmann spruce, after a spruce beetle epidemic because the created structure is more uniform with fewer groups and gaps than commonly observed in spruce-fir forests. With changing climatic conditions, proactive forest management, such as the shelterwood with reserves in the spruce-fir forest type, is the best method for increasing short-term resistance and long-term resilience to spruce beetle outbreaks. OPEN ACCESSForests 2015, 6 1158

Does the Practice of Silviculture Build Resilience to the Spruce Beetle? A Case Study of Treated and Untreated Spruce-Fir Stands in Northern Utah

“…Resistance metrics were based on Schmid and Frye's (1977) spruce beetle risk categories and focused on overstory structure and composition. However, Windmuller-Campione and Long (2015) as well as others Long 2012, Hart et al 2014b. ) observed that management, at best, provides only short-term resistance to the spruce beetle.…”

“…Because Engelmann spruce regeneration is key to maintaining spruce-fir stands after a spruce beetle epidemic, we define resilience based on a minimum amount of Engelmann spruce regeneration (Windmuller-Campione and Long 2015). Spruce regeneration, trees Ͻ1 in.…”

Adaptation of Forest Management Regimes in Southern Sweden to Increased Risks Associated with Climate Change

“…The annual increase of 0.4% per year corresponds to levels recorded during the peak bark beetles attack year of 2006, following the major storm Gudrun in 2005. Only trees with a diameter at breast height (dBH) larger than 20 cm were exposed to bark beetles damage [47]. The percentage of spruce bark beetle damage in the stand was calculated once every five years.…”

Applying Resilience Concepts in Forest Management: A Retrospective Simulation Approach

“…One framework to manage under this uncertainty is to increase forests resilience to disturbance [9][10][11][12][13]. In this study we use the resilience definition: "the capacity of a system to absorb disturbance and reorganize while undergoing change so as to still retain essentially the same function, structure, identity, and feedbacks" [14].…”

“…A second aspect of resilience is the degree of impact on forest ecosystems due to expected pests, disease, and drought. Changing the species, structural, and age class composition through management is another way to potentially lower the severity of disturbances thereby increasing resilience (e.g., [12,13,24,25]). Dymond et al [20] identified the potential benefits of greater tree species diversity in increasing socio-ecological resilience through proactive management of an extensive insect outbreak.…”