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Outbreaks Often Start with Wind Or Fire Damage Spruce Beetle

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May 2005 Forest Health Protection and State Forestry Organizations 4.6 WEB July 2010 Management Guide for Spruce Beetle By Steve Munson US Forest Service Dendroctonus rufipennis Kirby Topics Outbreaks 1 Host: Since the mid 1980’s, large stand- Management brief 1 Engelmann replacing spruce beetle epidemics have spruce occurred in southern and central Utah, Life history 2 Occasionally south central Idaho, north central Lodgepole pine Management 3 Washington, northwestern Wyoming considerations and on the Kenai Peninsula in Alaska. Stand hazard rating 4 Silvicultural 5 treatments Outbreaks often start with wind or fire damage Logging residue 6 and windthrow Population increases are often (Holsten et al. 1999), landslides, winter associated with blowdown, landslides, damage, and improper treatment of Direct suppression 7 stumps, residual large slash, and logging residuals (Wygant & Lejeune Natural controls 9 occasionally fire-weakened trees. If this 1967; McCambridge & Knight 1972). susceptible host material is not Epidemics are most common in Effects of spruce 12 available when adults emerge, they will overmature stands but may be sustained beetle attack and kill standing trees. As spruce in large pole and immature stands Recognizing trees 13 beetle populations increase, susceptible (Wygant & Lejeune 1967). Spruce attacked landscapes can be adversely affected by beetles will attack and kill trees 4-inch spruce beetle epidemics. diameter and larger (Schmid & Mata Other Reading 14 Outbreaks can develop at any time 1996). Periodic epidemics have Field Guide in mature spruce stands throughout the occurred throughout the west over the susceptible Engelmann spruce last 100 years. Management Guide component following blowdown Index Key Points Management Brief Blowdown events are often associated with spruce beetle Prevention; Partial harvest treatments to reduce the epidemics. proportion of spruce, reduce the average diameter of spruce, reduce stand density to create uneven-aged Use hazard rating to conditions. anticipate damage. Reduce hazard by Suppression; using trap trees, pheromone baits and altering stand lures, insecticidal sprays, sanitation and salvage conditions. harvests Trap trees are effective in reducing Clean up spruce logging residue and blowdown. local populations. Page 2 Back to menu Spruce Beetle 4.6 Life History Spruce beetle can have a 1 or 2- beetles may reemerge and attack green year life cycle. In the one-year cycle, trees from August through October, larvae complete their development over however most of the maturing brood the summer and overwinter as callow adults overwinter under the outer bark. (teneral) adults under the outer bark. Although it varies from tree to tree, a They complete their development the percentage of the adults reemerge and following spring emerging as sexually move to the base of the tree to mature adults (Hansen et al. 2001). In overwinter. Adult populations then the two-year cycle most of the beetles emerge the following spring attacking overwinter as larvae, although parent host material. Beetles in downed adults and eggs may also be present material do not emerge and move to under the bark (Schmid & Frye 1977). another site for hibernation. Most of Larvae resume feeding in the spring, the adult emergence occurs from mid- then pupate in galleries during late May to mid-July. spring-early summer of their second year. A small number of female adult Spruce Beetle— typical 2-year life cycle 4.6 Back to menu Spruce Beetle Page 3 Management Considerations: An overview Historically suppression efforts spruce beetle management areas. Spruce stands usually began after an infestation had should be caused substantial tree mortality. Suppress beetle populations designated as a Suppression activities emphasized Suppression activities may still beetle sanitation cutting, trap trees, occur in stands where preventative management or pheromone deployment and chemical treatments occurred. Treatments no-management spraying. Most spruce beetle designed to mitigate spruce beetle areas, susceptible spruce stands were impacts often result in stands with depending on unmanaged with few pre-outbreak some level of spruce beetle resource treatments designed to mitigate the susceptibility. Not all beetle objectives. effects of a spruce beetle outbreak. management designated areas will Forest managers can alter these post receive silvicultural treatments before mortem activities by initiating insect populations increase in treatments designed to reduce the susceptible stands. Thus, suppression effects of a spruce beetle outbreak. activities could become an integral part No-management Depending on resource objectives, of a spruce beetle management sites are spruce stands should be designated as a strategy. Suppression activities may generally beetle-management or no-management also be an option in treating sites near associated with area. Stands designated as no no management treatment areas if wilderness areas, National Parks, management sites would not be subject spruce beetle populations increase in no experimental to silvicultural or suppression management zones. Wherever forests and some treatments. Spruce beetle populations appropriate, suppression treatments roadless areas. would be allowed to fluctuate within should be linked to a silvicultural these no management sites. treatment to modify stand conditions that contribute to an infestation. Alter stand conditions to minimize The effectiveness of suppression outbreak potential treatments varies depending upon the Spruce stands designated as beetle action taken and the scale of the Hazard Rating management areas should be managed infestation. Because spruce beetle to minimize the effects of a spruce attacked trees do not fade until the Determine stand beetle outbreak. In beetle management following year, ground and aerial susceptibility to areas, resource managers should hazard surveys may not identify all the spruce beetle. rate stands to determine stand infested sites requiring treatment. In susceptibility to spruce beetle which which case, spruce beetle populations Develop will assist them with setting treatment would continue to expand in these non- treatment priorities. Suppression activities would treated sites. Suppression treatments priorities. occur within these sites if spruce beetle are most effective when most, if not all populations began to increase. Spruce of the infested areas are addressed and stands with multiple use objectives (i.e. the suppression treatments are recreation, wildlife and wood fiber administered correctly. production) are excellent candidates as Page 4 Back to menu Spruce Beetle 4.6 Example: Hazard/Susceptibility Rating (Schmid and Frye 1976) Step One: To calculate the hazard rating for a hypothetical Step one : To identify spruce stands susceptible to spruce beetle population stand assume the following increases, several stand and site attributes are used for the evaluation. The stand and site attributes: rating system is useful to determine what stand conditions could be altered to Site Index = 100 mitigate spruce beetle population increases. Avg. spruce dbh =17 in. Table 1 Stand Hazard Spruce in canopy = 70% 3 2 1 Evaluating these site and stand characteristics in Table 1, Physiographic Well-drained Sites with site Sites with site values of 2, 3, 3, and 3 are Location sites in creek index of 80-120 index of 40-80 obtained . bottoms Step Two: Adding these together results in a hazard Average diameter >16” 12-16” <12” rating value of 11. This is a of live spruce >10 “highly “ susceptible stand and inches dbh therefore at risk of sustaining significant mortality if spruce Percent of spruce >65 50-65 <50 populations increased. in canopy High Stand Risk: Indicates that the stand and site has attributes Step two: The potential risk rating is based on the summarized hazard that can contribute to rating obtained from the table. Risk indicates the amount of tree mortality population increases. that could occur if spruce beetle populations increased within the rated stand. Medium Stand Risk: Indicates the stand has Table 2 Stand Hazard some attributes that can Summary of Potential Hazard contribute to significant spruce mortality. Hazard Rating Rating Generally stands rated 11-12 High moderate risk may or may not contribute to 7-9 Medium population increases, 4-5 Low however during spruce beetle outbreaks most of the susceptible hosts Although this tree characteristic is not important in the lower 48 states, in within these Alaska large diameter spruce trees with slower than average growth rates intermediate rated were more likely to be attacked and killed by spruce beetle than trees with stands will be killed. growth equal to or greater than the stand average (Hard et al. 1983, Hard 1985, Holsten 1984, Doak 20). 4.6 Back to menu Spruce Beetle Page 5 Silvicultural Treatments Stands with epidemic spruce beetle Alexander (1973) suggests the should be left on site to following silvicultural options if minimize windthrow. spruce beetle populations pose a threat OR to susceptible stands. If more than the recommended If spruce beetle populations are percentage of basal area to be removed present in the stand to be cut or in is in susceptible trees, three options are adjacent stands affecting clumps available: of spruce (1) Remove all the susceptible AND trees, less than the recommended percentage of basal area to be (2) Remove the recommended removed is in susceptible trees, basal area in attacked and susceptible trees
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