Bark Beetle Outbreaks In Western North America: Causes And .
Bark Beetle Outbreaks inWestern North America:Causes and ConsequencesBeetle BarkSymposium,Snowbird Utah,November 2005
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Bark Beetle Symposium ParticipantsSnowbird, UT, November 15 – 18, 2005Barbara Bentz, Editor and Co-organizer, USFSRocky Mountain Research StationJesse Logan, Co-organizer, USFS Rocky Mountain Research StationJim MacMahon, Facilitator, Ecology Center, Utah State UniversityCraig D. Allen, USGS, New MexicoMatt Ayres, Dartmouth CollegeEd Berg, USFWS, AlaskaAllan Carroll, Canadian Forest Service, British ColumbiaMatt Hansen, USFS Rocky Mountain Research StationJeff Hicke, University of IdahoLinda Joyce, USFS Rocky Mountain Research StationWallace Macfarlane, GeoGraphics, Inc., UtahSteve Munson, USFS Forest Health ProtectionJose Negrón, USFS Rocky Mountain Research StationTim Paine, University of California at RiversideJim Powell, Utah State UniversityKen Raffa, University of WisconsinJacques Régnière, Canadian Forest Service, QuebecMary Reid, University of CalgaryBill Romme, Colorado State UniversitySteven J. Seybold, USFS Pacific Southwest Research StationDiana Six, University of MontanaDiana Tomback, University of Colorado, DenverJim Vandygriff, USFS Rocky Mountain Research StationTom Veblen, University of ColoradoMike White, Utah State UniversityJeff Witcosky, USFS Forest Health ProtectionDavid Wood, University of California at BerkeleyStaffHannah Nordhaus, writerMitchelle Stephenson, designi
BARK BEETLE OUTBREAKSIN WESTERN NORTHAMERICA: CAUSES ANDCONSEQUENCESAcknowledgementsWe thank Stephanie White, Paige Weed, Ryan Davis, Donovan Gross, and GretaSchen for assistance at the workshop and in manuscript preparation. Neil Cobb,Dave Breshears, and Cynthia Melcher provided helpful comments on the manuscript. For assistance with aerial overflight data of bark beetle impacts we thankJeanine Paschke, Gurp Thandi, and GeoGraphics, Inc. Elizabeth Grossmanassisted with an early version of the manuscript. Funding was provided by theUSDA Forest Service Rapid Science Assessment Team.ii
Report HighlightsSince 1990, native bark beetles have killed billions of trees across millions ofacres of forest from Alaska to northern Mexico. Although bark beetle infestations are a regular force of natural change in forested ecosystems, several of thecurrent outbreaks, which are occurring simultaneously across western NorthAmerica, are the largest and most severe in recorded history.There are many species of bark beetles, but only a few are responsible forthe large areas of dead trees we see today. These species colonize live andrecently downed trees, and kill either the entire tree or a portion of it during colonization and brood production. Bark beetle ecology is complex anddynamic, and a variety of circumstances must coincide for a bark beetleoutbreak to succeed on a large scale. Only when specific conditions aremet—ranging from suitable climatic conditions across an entire region, tothe particular forest structure and age, to the existence of certain bacteriaand fungi within the beetle and host tree—will bark beetle populationsgrow large enough to infest and kill trees across large landscapes.A bark beetle outbreakrequires: Abundant suitable hosttrees A climate favoring barkbeetle survival anddevelopmentAlthough outbreak dynamics vary from species to species and from forest to forest, the combination of two major factors appears to be driving the current outbreaks. Changing climatic conditions, in particular elevated temperatures anddrought: elevated temperatures can speed up bark beetle reproductiveand growth cycles and reduce cold-induced mortality during cold snaps.Extreme or prolonged water stress, caused by a combination of droughtand warm temperatures, can weaken trees, making them more susceptible to bark beetle attacks. Forest history and host susceptibility: many conifer forests in westernNorth America contain dense concentrations of large, mature trees thatare highly susceptible to bark beetle outbreaks. The factors that havecontributed to these conditions vary in relative importance from area toarea. They include large stand-replacing fires (both natural and humanset) and timber harvesting near the end of the 19th century—disturbances that resulted in large areas of forest of similar size and age. Insome areas, fire suppression over the last century also has inhibited thegrowth of new trees and created more dense stands. Because aggressivebark beetles favor mature trees, older, even-aged stands that haveregrown or been replanted after disturbance events such as wildfire andharvesting may be more vulnerable to future bark beetle outbreaksthan younger, more diverse stands. When trees must compete forresources in crowded conditions caused by either natural or humanprocesses, bark beetles can more easily overcome stressed trees’ defenses and initiate a severe outbreak.1
BARK BEETLE OUTBREAKSIN WESTERN NORTHAMERICA: CAUSES ANDCONSEQUENCESGiven the complexity of bark beetle community dynamics and the specific ecosystems they inhabit, the roles these factors play differ from forest to forest.Although research has uncovered a great deal of information about the life cyclesand host interactions of some species of bark beetles, many gaps in our knowledge remain. In addition, because changing climate and forest disturbances havealtered outbreak dynamics in recent years, some of what has been learned frompast outbreaks may no longer hold true. There may be no equivalent in the 100or so years of recorded history for the current outbreaks.These recent infestations may result in dramatic changes to the long-term ecological pathways of some ecosystems, radically shifting vegetation patterns insome hard-hit forests. The visual landscape cherished by many nearby landowners and visitors is altered as well, as once-green trees turn brown and then losetheir needles. In addition, bark beetle-killed trees pose some hazards when deadtrees fall in areas of forest that humans frequent.Although there are no known management options to prevent the spread of alarge-scale bark beetle outbreak, land-use activities that enhance forest heterogeneity at the regional scale—such as creating patches of forest that containdiverse species and ages of trees—can reduce susceptibility to bark beetle outbreaks. However, because resource objectives often differ, and because the factorsinfluencing a bark beetle outbreak vary depending on the species, host tree, localecosystem, and geographical region, there is no single management action that isappropriate across all affected forests.PHOTO BY JANE PARGITER, ECOFLIGHT, ASPEN COA whitebark pine forest in Yellowstone National Park. The red trees were attacked and killedby mountain pine beetles the year before the photo was taken in July 2007.2
IN THIS REPORT:Bark Beetle Ecology and Biology .6Aggressive Bark Beetle Species, Hosts, and Habitats.6Life Cycle and Life Stages of a Bark Beetle .8Bark Beetles and Temperature .10Bark Beetle Flight and Pheromone Plumes .12Bark Beetles and Trees .14The Community Beneath the Bark .15Bark Beetle Outbreaks.17Historical Bark Beetle Outbreaks .18Are the Current Outbreaks Different? .20Contributing Factors.23Climate.23Disturbance and Human Influence.26The Future of Our Forest Ecosystems .28Ecological Consequences of Recent Bark Beetle Outbreaks .28Bark Beetles and Fire .33Research Gaps.38Additional Reading .383
BARK BEETLE OUTBREAKSIN WESTERN NORTHAMERICA: CAUSES ANDCONSEQUENCESIntroductionTravel through a western North American forest today, and you will probablynotice large areas of standing dead trees with dry reddish-brown needles, orghostly gray snags from which all the needles have fallen. Across the West, fromAlaska to Canada, throughout the Rocky Mountain region and the southwesternUnited States, many forests and hillsides are now blanketed with trees that havebeen recently infested and killed by various species of bark beetles.New outbreaks ofmountain pinebeetle in BritishColumbia andAlberta are a signof expansionbeyond thebeetle’s recordedhistorical range.These outbreaks of aggressive bark beetles, which are occurring in numerous forest ecosystems across western North America, are the biggest inrecorded history. The term “aggressive” describes those species that can killeither the entire tree or a portion of it during colonization and brood production. Although western forests have experienced regular infestationsthroughout their history, the current outbreaks are remarkable for theirintensity, their extensive range, and their simultaneous occurrence in multiple ecosystems across the continent.These beetles are not only attacking forests where they have traditionallybeen found, but they also are thriving in some places where widespreadinfestations have not previously been recorded. Some outbreaks reflect theexpansion of at least one bark beetle species beyond its recorded historicalrange.With so many forests severely affected, land owners, land managers, policymakers, and the general public have taken notice. The extraordinary extent of theoutbreaks has prompted concern that this massive loss of trees may impairecosystem functioning and reduce the ability of our forests to provide futurewildlife habitat, to protect watershed quality, to store carbon, and to be a sourceof timber and recreational opportunities.Are the current bark beetle outbreaks unprecedented?Because it is technically difficult to reconstruct bark beetle outbreaks before the late 1800s, we areuncertain how extensive or severe outbreaks may have been prior to that time. However,scientists have examined outbreak frequency and severity over the last few centuries byexamining tree-ring growth patterns, and made inferences about bark beetle presence in forestecosystems prior to the last few centuries using ancient pollen and bark beetle remains. They alsouse computer models that describe how bark beetles respond to temperature to analyze beetlebehavior in the past and compare it to current outbreaks. In doing so, they hope to answer twoquestions.1) Is the scale of the current outbreaks—in terms of both geographic extent and the diversityand number of affected ecosystems—different from previously recorded outbreaks?2) Have the underlying dynamics and mechanisms of bark beetle systems been altered becauseof new inputs to the forest systems in which bark beetles live? For instance, have a warmingclimate, air pollution, and/or historical patterns of forest management and fires altered foresthabitat and beetle dynamics, allowing beetle populations to explode in recent years?4
Why are these unusual bark beetleoutbreaks occurring across westernNorth America, and what will they doto our forests? In November 2005,scientists with the USDA ForestService, Rocky Mountain ResearchStation convened a conference inSnowbird, Utah. Entomologists, ecologists, and foresters from across thecontinent shared the latest researchon bark beetle outbreaks and soughtto explain the causes, historical context, and short- and long-term consequences of the current outbreaks.This publication is a product of thatworkshop. It first explains how barkMountain pine beetle-killed lodgepole pine.beetles function within their nativeecosystems, and then examines therecent outbreaks and explains how they differ from previous recorded infestations. Finally, the report explores the ecological effects of the current outbreaksand identifies areas where more research may be needed so we better understand the causes and consequences of current and future infestations.The current bark beetle outbreaks differ from previously recordedinfestations because of:Their intensity — bark beetles are killing trees in larger numbers, at afaster pace, and over longer time periodsTheir extent — bark beetle outbreaks are occurring in numerousecosystems from Alaska to northern MexicoTheir synchroneity — bark beetle outbreaks are occurring concurrentlyacross western North America5
BARK BEETLE OUTBREAKSIN WESTERN NORTHAMERICA: CAUSES ANDCONSEQUENCESBark Beetle Ecology and BiologyNative insects, including bark beetles, are among the greatest forces of naturalchange in forested ecosystems of North America. Every few decades, depending on weather and local forest conditions, bark beetle populations increase andinfest large areas of conifer forest. In doing so, they play an essential role inforests’ natural cycle of growth andregeneration.A Source of Forest RenewalHistorically, bark beetles have not “destroyed” forests; rather,they have served as positive forces of transformation thatredistribute nutrients and growing space. Whereas older treesoften die en masse during bark beetle outbreaks, youngertrees are usually not attacked. Released from competition forlight, nutrients, and water, the young trees grow quickly toreplenish the forest canopy. Thus, bark beetles can helpmature forests regenerate. However, our understanding ofthe role bark beetles play in forests is based on observationsfrom the past few centuries. As climate and local ecosystemschange, the balance between bark beetles and their hostforests also may change.Bark beetles don’t just kill trees; theyalso have beneficial effects. For example,certain lodgepole pine cones require heatfrom forest fires, which are sometimesfueled by beetle-killed trees, to releasethe seeds within. In addition, becausebeetles generally attack larger trees,they serve an essential regenerativefunction—they help renew forests bykilling older and declining trees, allowing younger, more productive trees tocompete successfully for light, nutrients,and water.PHOTO A BY J.M. MILLERPHOTO B BY M. FURNISSThese photos show the same Tenaya Creek drainage in Yosemite National Park. The photo onthe left was taken in 1925, five years after a 1920 mountain pine beetle outbreak. The photoon the right, from 1984, shows how forests regenerate after beetle attacks.Aggressive Bark Beetle Species, Hosts, and HabitatsOf the hundreds of different North American bark beetle species, only a handfulof species (fewer than one percent) is considered aggressive, meaning the beetleskill all or a portion of the host trees they infest. These few species are primarilyresponsible for the large areas of tree mortality we see across the major forestecosystems of western North America, from the spruce forests of the far North tothe pine forests of the southwestern U.S.6
The tree-killing bark beetles reside in a single family of insects (Curculionidae,subfamily Scolytinae), and each species has evolved to feed and reproduce in asingle conifer group (Table 1). The Douglas-fir beetle, for instance, is found exclusively in Douglas-fir trees across western North America. The mountain pinebeetle attacks and reproduces in at least 12 different species of North Americanpine across a number of ecosystems, from sea level to 10,000 feet in elevation,from the Pacific coast to the Black Hills of South Dakota, and from BajaCalifornia to central British Columbia. Its range has historically been limited byclimate, not by the availability of host trees. For instance, although lodgepolepine trees are found as far north as northern British Columbia, western Alberta,and the Yukon and Northwest Territories, those areas until very recently hadbeen untouched by mountain pine beetle. In recent years, however, mountainpine beetle outbreaks have been recorded in northern British Columbia andwestern Alberta; lodgepole pine forests in the Yukon and Northwest Territoriesstill appear to be free of bark beetles.TABLE 1.Aggressive Bark Beetles and their Host Trees in the Western U.S. and CanadaCOMMON NAMESCIENTIFIC NAMEMAJOR HOST TREE SPECIES IN THE U.S AND CANADAmountainpine beetleDendroctonusponderosaelodgepole pine, ponderosa pine, bristleconepine, whitebark pine, western white pine,sugar pine, limber pine, and othersspruce beetleDendroctonusrufipennisEngelmann spruce, white spruce,Lutz spruce, Sitka spruceDouglas-fir beetleDendroctonuspseudotsugaeDouglas-firwestern pinebeetleDendroctonusbrevicomisponderosa pine,Coulter pinesouthern pinebeetleDendroctonusfrontalisApache pine,Chihuahua pine,ponderosa pineArizona fivespinedipsIps leconteiponderosa pinepiñon ipsIps confususpiñon pinewestern balsambark beetleDryocoetes confusussubalpine firfir engraverScolytus ventraliswhite fir, California red fir, grand firPHOTO BY DANIEL RYERSONAdult piñon ips beetles are only 0.12 to 0.14inches long—barely larger than a grain ofrice. Mountain pine beetles are slightly larger, around 0.20 inches, while spruce beetlesaverage 0.22 inches long.7
BARK BEETLE OUTBREAKSIN WESTERN NORTHAMERICA: CAUSES ANDCONSEQUENCESPonderosa pines generally are found at lower elevations.Species within the genus Ips, such as the piñon ips andArizona fivespined ips, also can kill their hosts, although typically they are not considered major disturbance agents. Inrecent years, however, elevated population levels of a numberof Ips species have coincided with drought, resulting in largeareas of mortality, particularly in piñon and ponderosa pineforests of the southwestern U.S.Life Cycle and Life Stages of a Bark BeetleNative North American bark beetles in the generaDendroctonus, Dryocoetes, Ips, and Scolytus live, feed on,and lay their eggs in the soft living tissue of a tree, known asthe phloem, which lies just below the tree’s protective outerbark layer. These small beetles are 1/8th to 1/4 inch long,dark brown to black, and cylindrical in shape. Bark beetlelarvae, which develop from eggs laid inside the tree, arewhite and less than 1/4 inch long, thus resembling a grain ofrice. After maturing through four life stages—egg, larva,pupa, and adult—they emerge as new adults from the hostWhitebark pines are found tree and fly to a new live tree, where they mate and lay eggsat higher elevations in thenorthern Rocky Mountains to begin the cycle again (Figure 1).of the U.S. and in theCanadian Rocky Mountains,as well as in Oregon,Washington, and California.8Bark beetle life cycles range from a few weeks to two or threeyears, depending on the species and climate in which thebeetles are found. Adult beetles attack their host trees during
the time of year when they are most vulnerable—for example, spruce, true fir,and Douglas-fir trees are less able tofend off a beetle attack when their rootsare still under snow. Bark beetles typically attack these trees in late spring,
i Bark Beetle Symposium Participants Snowbird, UT, November 15 Ð 18, 2005 Barbara Bentz,Editor and Co-organizer, USFS Rocky Mountain Research Station Jesse Logan,Co-organizer, USFS Rocky Mountain Research Station Jim MacMahon,Facilitator, Ecology Center, Utah State University Craig D. Allen, USGS, New Mexico Matt Ayres, Dartmouth College Ed Berg, USFWS, Alaska
European Chafer, Asiatic Garden Beetle, Oriental Beetle, Black Turfgrass Ataenius) There are 8 different white grubs that are commonly known to cause turfgrass plant damage. They include the Japanese beetle, May and June beetle, masked chafer, green June beetle, European chafer, Asiatic garden beetle, oriental beetle, and black turfgrass ataenius.
well defended against the new beetle species. Furthermore, recent work in Canada suggests that host trees growing in regions that historically have been climatically inhospitable to bark beetles, may be less resistant to beetle attacks than trees of the same species growing in areas where outbreaks have historically occurred (Cudmore et al. 2010).
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10.3.5 Connecting ADC and DAC IPs into a Cortex-M system 242 10.4 243Bring an SoC to life – Beetle test chip case study 10.4.1 Beetle test chip overview 243 10.4.2 Beetle test chip challenges 245 10.4.3 Beetle test chip system design 246 10.4.4 Implementation of the Beetle test chip 24
resulting from bark beetle outbreaks has been identified as a priority research issue for enhancing ecologic-economic resilience in forested areas at risk [11]. . upon decision utility (that is, utility as expressed in the decisions that people make to satisfy their . track very closely with the magnitude of MPB-caused tree mortality .
Figure 12: Adult twice-stabbed lady beetle with several pre-pupae and pupae on a crape myrtle trunk. It is not unusual to see many lady beetle pupae on the trunk of an infested tree. Before pupating, these beetles cleaned most of the scales from this tree. Lady beetle pupae are the pre-adult stage of the lady beetle and are highly beneficial.
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