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

Abstract

Silviculturists are under increased pressure to develop treatments that increase resistance and resilience to the spruce beetle (Dendroctonus rufipennis Kirby). Multiple silvicultural systems (i.e., group selection, shelterwood with reserves, and others) have resulted in some short-term increases in resistance. However, less is known about how silvicultural systems, especially ones used over many decades, impact resilience; resilience is defined as a minimum amount of Engelmann spruce (Picea engelmannii Parry ex Engelm.) regeneration to ensure continuity of a spruce component in the future stand. To further explore these concepts, silviculturally treated and untreated stands were sampled after a recent landscape-scale spruce beetle epidemic in northern Utah on the Uinta-Wasatch-Cache National Forest. Both treated and untreated stands had no resistance to the spruce beetle but differed in their resilience. Treated stands had increased resilience due to greater and more consistent stocking of Engelmann spruce regeneration than the untreated stands. When silvicultural systems are developed, special attention should be paid to ensure that conditions created after harvests are conducive for regeneration of the desired species (spruce).

Monitoring resistance and resilience using carbon trajectories: Analysis of forest management–disturbance interactions

“…Shelterwood cuts have been recommended by others to increase stand resilience (e.g., Temperli et al, 2014;Windmuller-Campione et al, 2017), but our data indicate that shelterwood treatments were not different from non-treated control stands in terms of short-term resilience. However, over a longer time-since-outbreak time series, this result could potentially change as Engelmann spruce recruitment continues to increase.…”

Building Resistance and Resilience: Regeneration Should Not be Left to Chance

“…There is ample evidence for successfully building stand and landscape resistance to different types of disturbances, for example wind and fire (e.g., [32,33]). While manipulating stand structure and composition so as to build resistance to bark beetle attack is certainly feasible [31], there is considerable evidence that it will ultimately fail in the face of overwhelming beetle numbers [19,31,[34][35][36]. Indeed, building stand resistance to bark beetle attacks may not be a good use of management effort and limited resources unless explicitly used to further a resilience goal.…”

“…Indeed, building stand resistance to bark beetle attacks may not be a good use of management effort and limited resources unless explicitly used to further a resilience goal. Short-term resistance can, however, buy time in which desirable regeneration can be established, and this may be critical to building post-outbreak resilience [19,34]. Table 3.…”

“…This system has been favored because it is thought to mimic gap-phase dynamics and typically results in successful natural regeneration of spruce. After several cutting cycles, the resulting structural and compositional diversity offers considerable resilience to a spruce beetle outbreak, represented by multiple age-classes and tree species diversity [34]. However, for stands in which it is currently lacking, the timely building of resilience with the small group selection system is constrained by the length of the cutting cycle and the small percentage of total area regenerated per entry.…”

Important Insect and Disease Threats to United States Tree Species and Geographic Patterns of Their Potential Impacts

“…When considered within its full ecological context, some amount of disturbance by insects and diseases can play a role in sustaining a healthy forest structure by culling weaker competitors and releasing resources necessary for the growth of surviving trees [5,6]. Such a perspective is limited to the effects of native insect and disease agents, however, while noting that the effects of at least some insect and disease agents on forest structure and composition may have been magnified by long-term forest management practices (or the lack thereof) [7][8][9] and could become stronger and more widespread with projected climate conditions [3,10,11]. At least some non-native insects and diseases, meanwhile, cause undeniably devastating impacts to forests, including wholesale alterations to the structure and functioning of forest ecosystems [12].…”