Outbreaks Often Start with Wind Or Fire Damage Spruce Beetle

Home , Bark beetle, Enoclerus sphegeus, Spruce

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 and accept Action: the risk of future losses Any attacked and all susceptible trees should be (3) Leave the stand uncut. If the removed in the first cut. stand is left uncut and a spruce This silvicultural option will beetle outbreak occurs, most of remove most of the larger the susceptible spruce basal Engelmann spruce killed by spruce thus affecting wind area will be lost and surviving spruce beetle on the Manti- firmness of the residual spruce would be smaller LaSal NF in Utah. spruce. Non-hosts and smaller diameter (<5” dbh) (Dymerski diameter spruce (<10-12” dbh) et al. 2001).

Stands with endemic spruce beetle Uneven aged prescriptions for Small, ¼ acre openings will spruce-fir stands will not prevent promote spruce regeneration losses caused by spruce beetle but within these uneven aged systems. they will mitigate the effects of an Stand entry should occur before outbreak within a treated area. Table 3 the stand reaches 60 percent summarizes post-harvest diameter maximum SDI to sustain a lower class distribution where a full range of spruce beetle stand hazard rating. diameter classes is the objective for an uneven-aged prescription. The uneven-aged prescription provides an average diameter of 7.5 Table 3 Example: Uneven-aged stand with low inches, a stand density index (SDI) of spruce beetle potential 35 percent of maximum and a basal 2 Mid-point Stand Density Basal Trees/ area of 134 ft per acre. This spruce-fir dbh Index Area acre prescription will generally meet visual and wildlife objectives while reducing 2 15 4 197 stand density to a lower degree of full site utilization (thus allowing for 6 50 25 125 maximum individual tree growth). 10 60 33 60 14 60 37 35 18 50 35 20 Total 235 134 437 Page 6 Back to menu Spruce Beetle 4.6

Treat Logging Residuals

Guidelines for addressing logging Except for complete elimination of residuals were developed by Schmid host material, even the previous (1977) to minimize spruce beetle recommendations will not keep beetles populations increases. from inhabiting the bottom surfaces of logs and tops. If high beetle  Minimize stump heights leaving populations are subsequently found in stump heights of no more than 1.5 these surfaces, they should be treated feet. by removing the outer bark (peeling knife or log wizard) or burned.  Cull logs and tops should be If a significant spruce beetle limbed and the branches moved to population exists in the adjacent forest reduce shade on bole surfaces. (clumps of infested trees), the logging residuals could be used to trap Log Wizard is used to remove  After limbing, cull logs and tops dispersing adults. Adult beetles prefer outer bark of spruce beetle should be moved from shady sites downed host material; however there infested logs. to sunny areas and not piled unless could be a spillover effect, as some they will be burned. adult insects will attack adjacent standing hosts. Any infested down or  Cutting logs and tops into short standing material should be removed, lengths (18-inches) will promote burned or peeled following adult Any infested down drying of the phloem reducing the beetle flight. or standing amount of suitable habitat for The logging residual guidelines material should be developing larvae. are applicable under selective, removed, burned or shelterwood, or clearcut silvicultural peeled following  While full-length logging removes systems. The selective system provides adult beetle flight. the merchantable host material, more shade than the other treatments. complete removal or destruction of Under a selective system prompt all cull logs and tops would removal or destruction of suitable host eliminate suitable host material for material is the best strategy to developing life stages. If trees are minimize spruce beetle population logged full length, the diameter of increases. the small end should be 4 inches.

Clean up windthrown trees Windthrown susceptible spruce densities in the downed material using are the most important contributors to the sampling scheme developed by spruce beetle population increases Schmid (1981). Remove infested (Schmid & Mata 1996). Windthrow If the windthrown trees are windthrown trees from moderate to events that occur in stands rated infested, removing infested trees from high hazard sites. moderate to high hazard may result in susceptible sites is the preferred outbreak populations of the insect. option. Salvage programs in Utah Not all windthrow events lead to have used a variety of treatments to spruce beetle population increases. suppress spruce beetle populations in Scattered windthrow in late winter or sites where windthrow occurred, spring is the most conducive to including; salvage of infested trees, population increases. using Lindgren funnel traps baited Windthrown trees should be with the 3-component spruce beetle sampled in late July-August following attractant pheromone and trap trees adult flight to determine attack (Bentz & Munson 2000). 4.6 Back to menu Spruce Beetle Page 7

Direct Suppression Preventative Sprays Carbaryl - Carbaryl (Sevin) is Preventive insecticide applications registered as a preventive insecticide must be applied before adult beetles treatment for spruce beetle. Several attack the tree. Because of application flowable formulations are commonly costs associated with individual trees, used including, Carbaryl 4L, Carbaryl preventative treatments are generally 4F, Sevin XLR Plus and Sevin SL. Do reserved for high value trees, i.e. not use wettable powders; they are recreation areas, administrative sites ineffective with low residual efficacy. and ornamentals. Remedial Sprays Carbaryl applications applied Preventative sprays are applied correctly, are effective for two years using hydraulic sprayers with pump Although chemical following treatment. pressures that reach 350-450 psi insecticides have (pounds per square inch). Nozzle been used in the Other Insecticides - Pyrethroid field orifice sizes range from #8 to #10. The past to kill trials are currently being conducted in higher pump pressures are necessary to developing larvae in infested trees, central Utah. Various rates of the reach up to 50 feet on the tree bole of no products are pyrethroid formulations are being large diameter trees. Trees with currently abundant branching on the lower evaluated for efficacy. There are no registered for this registered pyrethroids for spruce beetle portions of the bole should be pruned type of treatment. at this time. up to 10-12 feet to enhance treatment performance. All bole surfaces must be sprayed to the point of runoff, including the root collar and exposed surface roots. Trapping During endemic population (Wygant 1960). The number of trap phases, spruce beetles maintain trees felled depends on the level of populations in windthrown trees. They infestation and size of the infested prefer downed material to standing trees. In static infestations, the green trees. Trap trees are used as a number can range from 1-10 suppression tactic because of this depending on the diameter of standing preference for downed trees. Trees infested trees and the diameter of trap selected as trap trees, are green large- trees, larger diameter trap trees absorb diameter trees (>16 inches dbh) felled more beetles (McComb 1953). In to attract attacking adult spruce building infestations, the number of beetles. trap trees ranges from 1-5 based on the Trap trees are either burned, same parameters used for determining peeled or removed before beetle number of trap trees for static emergence the following spring to infestations (Nagel et al. 1957, Wygant ensure that no one year brood adults 1960). Removing the bark from will disperse to standing trees. Standing trap trees baited with an spruce beetle infested trap Trap trees should be felled in the attractant pheromone (tree bait) are trees is an effective, if time- shade and left intact and unlimbed effective but attract fewer beetles than consuming, means to destroy the brood. (Hodgkinson 1985, Nagel et al. 1957, downed trap trees. Adjacent to felled Wygant 1960). They are most or standing trap trees, other susceptible effective if felled in the spring before host trees will often be attacked. To adult beetle flight (Hebertson 2004, suppress beetle populations, all McComb 1955). Felled trap trees often standing and down infested trees attract 10 times or more the number of should be treated before beetle adult beetles that attack standing trees emergence the following spring. Page 8 Back to menu Spruce Beetle 4.6

Trapping (continued) Trap trees not treated by the following due to the pitch produced by the non- spring before adult flight, will add to host baited tree (Dyer & Safranyik further tree mortality. Forest 1977). Lethal trap trees, which are Non-host trees entomologists can assist resource felled or standing host trees baited baited with the managers with determining the with the spruce beetle lure and sprayed attractant number and placement of trap trees with a preventative insecticide, have pheromone are necessary to mitigate spruce beetle not been as effective at suppressing potential trap population increases. populations compared to the trees. Non-host trees baited with the traditional trap tree approach described attractant pheromone are also potential previously. trap trees because reproduction is prevented and many parent adults die

Pheromone strategies Spruce beetle attractant  Cluster Baiting – A tree bait is pheromones have been used to placed in 3-bait clusters at 330 suppress localized populations of the foot (5 chain intervals). Within insect. There are two methods of each cluster, place individual baits deploying attractant pheromones: tree 30-50 feet apart. This is an baits and spruce beetle lures. effective technique for low or MCH endemic spruce beetle populations (3-methyl-2- Tree Baits – to concentrate dispersing adults. cyclohexen-1-one) Polymer bubble caps containing All baited trees and adjacent The natural the attractant pheromone are stapled to attacked trees must be removed, antiaggregant green susceptible host trees. Tree baits burned or peeled to eliminate the pheromone for are an effective tactic if used in sites developing life cycles from the treated Douglas-fir beetle where spruce beetle populations are areas. Because of the possibility of a repels spruce beetle endemic or low. Baiting tactics are as one-year life cycle, the trees must be attacks, particularly if populations are follows: treated the same year the baits were endemic or just  Spot Baiting – Used to suppress installed following adult spruce beetle beginning to small pockets of infested trees dispersal. increase. (<30 trees). Bait 2-3 susceptible trees in the center of each spot Spruce Beetle Lures — Previous field studies spaced 30 to 50 feet apart. Spruce beetle attractants are used indicate MCH can  Mop-Up Baiting – Used to for monitoring purposes and to reduce attacks on concentrate residual beetle supplement suppression efforts. MCH treated populations following harvest. Recent attractant studies in Utah windthrown trees and Bait trees within or surrounding indicate that the 3-component lure is a logs (Rudinsky et al. the treated area at 75-150 foot more effective attractant for spruce 1974). MCH used as intervals. Baits should be beetle (Ross et al. 2005). However, a repellent in deployed for two years to spillover effects on adjacent host trees outbreak populations effectively cover the 2-year life are greater when the 3-component lure of spruce beetle, is cycle spruce beetles. is used. To minimize this effect, not an effective  Grid Baiting – Used in infested funnel traps with lures should be treatment (Ross et sites up to 50 acres to contain placed at least 100 feet from a al. 2004). beetles within currently infested susceptible host tree. Trap placement boundaries. Bait single standing should occur in clumps of non-hosts or trees at 75 foot intervals. dead spruce. Trap placement in open areas without shade, is not very effective. 4.6 Back to menu Spruce Beetle Page 9

Pheromone strategies (continued)

Monitoring – Suppression – Spruce beetle lures are used in Lindgren funnel traps baited with combination with Lindgren funnel the 3-component lure is an effective traps to determine flight periodicity strategy to reduce local populations of and population densities. A Lindgren the insect. This technique is most funnel trap baited with the 2- effective if used in combination with component lure is an effective other suppression treatments (i.e. monitoring technique. Single traps sanitation, trap trees). Traps should be placed in sites with spruce beetle placed in 3 trap clusters at 330-foot activity will effectively monitor flight intervals (5 chains) in clumps of non- activity and population densities. hosts or dead spruce. Distance between traps within a cluster should range between 50-75 feet. A funnel trap containing aggregative semiochemicals provides a means to assess and reduce local populations Natural Controls of spruce beetle.  Temperature extremes  Woodpeckers  Insect predators and parasites

Temperature extremes

Temperature is one of the most bark subjected to such conditions. critical factors in the life of the spruce Temperatures above 110°F will kill beetle; the extremes are lethal, and the varying percentages of the brood intermediates influence development. depending on the length of exposure Extremely low (Mitchell & Schmid 1973). spring Extreme cold— temperatures in Laboratory tests showed that Adaptation to cold— Colorado in 1951 subcortical temperatures of -15°F will The overwintering behavior of a are frequently cited kill all adults, while -30°F will kill all percentage of the adults may have as a major factor in larvae (Massey & Wygant 1954). evolved in response to cold winter terminating the Extremely low temperatures in temperatures. When beetles leave the White River Colorado in 1951 are frequently cited upper bole and reenter the bark near outbreak as a major factor in terminating the the base, their survival is enhanced. White River outbreak (Wygant 1956). Under normal conditions, 6 feet or In the northern Rocky Mountains, an more of snow accumulates on the average of 42 percent of the brood was ground in the high elevation spruce-fir killed during an unusually cold spell forest covering the tree base. Below (Terrell 1954). this snow line, temperatures are near 32°F while above the snow line Extreme heat— ambient air temperatures exist. Thus, At the opposite extreme, beetles in the bark below the snow line temperatures exceeding 130°F for 30 are not subjected to lethal sub-freezing minutes will kill all the brood in the temperatures (Schmid & Frye 1977). Page 10 Back to menu Spruce Beetle 4.6

Woodpeckers

Three species of woodpeckers, the greater because this species northern three-toed, the hairy, and the aggregates in infested areas downy, are important predators of the (Koplin 1969). spruce beetle and are listed in  The hairy woodpecker feeds on decreasing order of importance the trunks of trees including old (Knight 1958). snags in addition to freshly attacked trees (Koplin 1969). Three important bird species—  The downy is the least effective  The northern three-toed is most spruce beetle predator of these effective because it feeds three species of woodpeckers. It exclusively on the boles of trees, feeds mainly on the branches of primarily on trunks of freshly infested trees (Koplin 1969) and attacked trees rather than old snags has the least pronounced (Koplin 1969) and is indigenous to functional response to infestations the spruce-fir habitat (Baldwin (Koplin 1972). 1960). Its effectiveness is also

Natural Controls  Weather: temperature extremes have been credited with ending some spruce beetle outbreaks  Woodpeckers: such as the northern three-toed woodpecker, feed exclusively on insects in the bole of trees. During an outbreak, woodpeckers can consume  Insect predators and parasites: Effects are quite as much as 55% of the variable, from minimal to more than 60 percent. spruce beetle brood.

Impact on bark beetle populations— downed material may be reduced. Woodpecker effects on beetle When absent, woodpeckers may populations are influenced by host concentrate on the downed material. material, density of beetle brood and Feeding activity of woodpeckers extent of woodpecker feeding. During fluctuates with the season, day, outbreak conditions in standing trees, weather, and the type and amount of woodpeckers may destroy 55 percent infested host material. Feeding on of the brood (Hutchison 1951) infested standing trees is generally although beetle mortality may vary highest during December through from 45 to 98 percent (Knight 1958). March; feeding is greatly reduced on During low-level infestations such trees from late May to September woodpeckers may only take about 20 (Koplin & Baldwin 1970). percent of the brood in standing trees. Despite high-energy needs and In trap trees or downed material exclusive feeding on spruce beetle in woodpeckers may consume 2 to 26 winter, woodpeckers would be unable percent of the brood (Koplin & to eliminate all the beetles in each tree Baldwin 1970). Feeding activity on because of the overwintering behavior trap trees or downed material may be of a percentage of the adults in the influenced by the presence or absence base of the tree beneath the protective of adjacent infested standing trees. snow cover. When present, feeding activity on the 4.6 Back to menu Spruce Beetle Page 11

Natural Controls

Insect Predators and Parasites

The effects of insect parasites and Important species— predators on spruce beetle populations Generally the important parasitic are quite variable. These agents are a and predacious species are known (Massey & Wygant 1954, Jensen tremendous mortality factor in some Insect parasites infestations; perhaps accounting for 1967). Their life cycles, habits, and and predators more than 60 percent beetle mortality. mortality effects of some species are In other cases, the entomophagous known either from studies of the These agents are a species kill a large number of spruce spruce beetle or other Dendroctonus tremendous beetles, but their effect on the beetles (Schmid and Frey 1977). mortality factor in population is minimal. some infestations;  The most important Braconid perhaps accounting Impact on spruce beetle wasp parasite is Coeloides for more than 60 outbreaks— dendroctoni. Two other parasitic percent beetle Some forest entomologists believe wasps have been observed feeding mortality. insect parasites and predators are on spruce beetle larvae. Both are primarily responsible for keeping Pteromalididae wasps with little beetle populations at endemic levels. known about their life history or However, the fact remains that habits. Neither species are infestations develop from a low level considered to be important to outbreak status with these contributors at suppressing spruce organisms present. Furthermore, under beetle populations. outbreak conditions these organisms seldom cause a rapid reduction of the  The second most important beetle population to pre-outbreak biological mortality agent of levels even though they may kill a spruce beetle besides woodpeckers large number of beetles. is a parasitic fly Medetera aldrichii. Its effectiveness may be lessened by indiscriminate feeding habits because larvae feed on a variety of other insects (Massey & Based on these Wygant 1954). observations, it is difficult to  Three species of clerid beetles also conclude that natural feed on spruce beetle life stages, populations of insect Parasitic wasps help to keep Thanasimus undatulus, Enoclerus bark beetle populations in parasites and predators lecontei and Enoclerus sphegeus. check. regulate spruce beetle populations.  Other insect species have been observed feeding on various developmental stages of the beetle. Few of these have been adequately studied and their effectiveness as predators is not known. Page 12 Back to menu Spruce Beetle 4.6

Effects of Spruce Beetle Significant succession Vegetation— Affected stands become predominately effects of spruce When epidemic spruce beetle fir for the next 125-175 years or until beetle include populations change stand structure, the fir begins to die (Schmid & Hinds rapid conversion they also simultaneously alter species 1974). to fir cover composition. Stands composed of 90 Forage production in beetle-killed types, and percent spruce and 10 percent fir in the stands is much greater than in green increased overstory before the White River unaffected stands. Grasses and sedges density and outbreak became 20 percent spruce showed increased density in beetle- diversity of and 80 percent fir in the overstory after killed stands and forbs were 2.3 times grasses and the epidemic (Schmid & Hinds 1974). more numerous but browse plants forbs. In Utah on the Wasatch Plateau, decreased. In general, the greatest the spruce beetle outbreak reduced density, number of species, and index spruce basal area more than 90 percent of occurrence of plants were found in and decreased average spruce beetle-killed stands (Yeager & diameters from 14.1 inches to 8.6 Riordan 1953). inches (Dymerski et al. 2001).

Wildlife— declining in abundance. The influence of spruce beetle Seed eating birds and mammals epidemics on animal populations are adversely affected because of the inhabiting spruce-fir forests has not loss of spruce seed (Yeager & Riordan been determined but would depend on 1953). Spruce grouse would also Elk and deer may find the species requirements and the decline in numbers because of the loss improved forage after a intensity and range of the epidemic of suitable habitat and winter food. In spruce beetle epidemic. (Schmid & Frye 1977). Insectivorous contrast, elk and deer benefit from the birds such as woodpeckers would increased forage production, although initially increase because of the the loss of thermal cover can be abundant food supply, however as detrimental to both species (Schmid & insect populations decreased these Mata 1996). predators would have to emigrate thus

Fire— In contrast, fire intensity (the Spruce beetle epidemics can destructive nature of a fire) would In the aftermath of influence both fire hazard and fire increase after a spruce beetle a spruce beetle intensity. Increased fire hazard infestation and remain at a higher level epidemic, the risk (probability of a fire starting) created for decades because of the increased of increased fire by the killing of spruce by beetles is amount of dead fuels that are slow to intensity remains limited to the first two years after decay (Schmid & Mata 1996). The high for several beetle attack when the dead and dying probability for stand replacing fires in decades because needles increase the fine fuel a spruce beetle affected site remains the large dead component. Once these fuels fall from small because fires are infrequent in fuels are slow to the dead trees, fire hazard is essentially spruce-fir forests (Veblen et al. 1994). decay. similar to the period before the trees However, if a fire started under were attacked and killed by spruce favorable or extreme fire weather beetle (Schmid & Mata 1996). coniditons the abundant fuel loads would increase fire intensity. 4.6 Back to menu Spruce Beetle Page 13

Effects of Spruce Beetle (continued) Hydrology— epidemic (Bethlahmy 1974). Spruce beetle epidemics influence Following the White River spruce tree-water relationships and if the beetle outbreak in Colorado, Loss of riparian epidemic is large enough, streamflow. streamflow for the affected watershed forest canopy A long-term streamflow study in increased 1.6-1.9 inches (Mitchell and following a Colorado following a spruce beetle Love 1973). spruce beetle epidemic found that a major increase epidemic can in streamflow occurred after the result in increased stream flows.

Deterioration of Spruce— In the White River spruce beetle Mielke (1950) studied the rate of outbreak in Colorado (1941-1952), tree deterioration in beetle killed Hinds et al. (1965) found that about 40 Engelmann spruce. In southern Utah, percent of the original cubic volume 85 percent of the spruce beetle killed had been lost 20 years after the trees trees were still standing after 25 years. died. About one-third of this loss was Mielke also studied this effect in due to decay in standing trees, two- Colorado and noted that the moisture thirds to windthrow. As time passed, content of heartwood and sapwood had windthrow was a progressively more reached such a low level in the dead important deterioration factor. spruce that decay fungi were unable to Boring dust on the bark is develop. often the most obvious sign of successful spruce beetle attacks. Pitch tubes may occur on the bark of Recognizing Trees attacked by Spruce Beetle attacked trees. Reddish-brown boring dust on alternate sides of the gallery, which is bark, in bark crevices, and on the packed with frass and boring dust. ground around the root collar from Larvae feed in the phloem outward mid-May to mid-July is the most from the egg gallery, often in a obvious sign of beetle attack. Pitch radiating pattern. The needles on tubes may also occur around entrance infested trees usually do not turn sites. Boring dust and pitch tubes are yellowish-green until the following most visible the first summer summer, one year after the initial following initial attacks (Holsten et al. attacks. Needle discoloration 1999). During winter, woodpeckers generally takes place in late July and feeding on overwintering life stages August. Needles drop soon after produce bark flakes that accumulate on fading as a result of wind and rain. the ground or snow around infested Adult beetles are dark brown to black trees. Egg galleries average about 6-8 with reddish-brown or black wing inches in length, have a slight crook at covers and are about 1/4 inch long and Pitch tubes may occur the start, and extend vertically in 1/8 inch wide (Holsten et al. 1999). around beetle entrance sites on the bark. standing trees. Eggs are deposited on Page 14 Back to menu Spruce Beetle 4.6