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 The Northwest and Alaska Fire Research Clearinghouse

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Spruce Beetles and Forest Ecosystems of South-Central Alaska
From 1990 to 2000 a massive outbreak of spruce beetles (Dendroctonus rufipennis) caused a die-off of spruce trees (Picea spp.) across more than 1.19 million ha of forests in Alaska. This natural disturbance was most pronounced among forests in south-central Alaska where a variety of research studies were initiated to examine both the causes of this outbreak and its far reaching effects on human, plant, and wildlife communities in the region. The majority of these studies have only recently been completed and few have been published. Information from these studies, however, are of considerable interest to the public, land managers, and scientists alike as the recent spruce beetle outbreak was both the largest recorded from North America and the most significant disturbance event in a terrestrial ecosystem in Alaska since the Good Friday earthquake of 1964. In February 2004, the symposium 'A changing Alaskan ecosystem: the effects of spruce beetle outbreaks and associated management practices on forest ecosystems of south-central Alaska' was held in Homer, Alaska. A special issue of the Forest Ecology and Management journal published a number of papers invited from the 69 papers originally presented at the symposium. The goal of both the symposium and this special issue was to update the understanding of spruce beetles and forest ecosystems of southcentral Alaska. The papers included in the special issue present both an exhaustive review and synthesis of previous research findings (Werner et al. 2006), and new insights from seven original research papers. These latter papers provide fresh perspectives into the ecological and socioeconomic effects of spruce beetle outbreaks as viewed by local residents living in infested landscapes (Flint 2006); long-term natural disturbance regimes by spruce beetles (Berg et al. 2006) and fire in infested forests (Berg and Anderson 2006); effects of outbreaks on landscape-level stand dynamics (Allen et al. 2006), plant succession (Boucher and Mead 2006), and berry production (Suring et al. 2006); and the effects of different management prescriptions on infested forests (Goodman and Hungate 2006). Ideally these papers will help encourage future research on bark beetles (Dendroctonus spp.), stimulate the development and implementation of policies that address the causes and effects of their outbreaks, and ultimately help maintain the socioeconomic values and ecological integrity of forests infested by bark beetles both in south-central Alaska and elsewhere in North America.

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Spruce Beetles and Forest Ecosystems in South-Central Alaska: A Review of 30 Years of Research
From 1920 to 1989, approximately 847,000 ha of Alaska spruce (Picea spp.) forests were infested by spruce beetles (Dendroctonus rufipennis). From 1990 to 2000, an extensive outbreak of spruce beetles caused mortality of spruce across 1.19 million ha of forests in Alaska; approximately 40% more forest area than was infested the previous 70 years. This review presents some of the most important findings from a diversity of research and management projects from 1970 to 2004 to understand the biology, ecology, and control of this important forest insect, and the causes and effects of their outbreaks. It is suggested that future research should examine the long-term effects of the spruce beetle outbreaks and climate variability on forest ecosystems in the region. Research into how different management actions facilitate or interrupt natural successional processes would be particularly useful.

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Community Perspectives on Spruce Beetle Impacts on the Kenai Peninsula
A recent outbreak of spruce beetles (Dendroctonus rufipennis) in forests on the Kenai Peninsula, Alaska was met with substantial variation in response among people and communities situated within this changing landscape. Interviews and mail surveys administered to residents in six Kenai Peninsula communities revealed differences in perception of biophysical, social, and economic impacts that resulted from changing forest conditions related to the spruce beetle outbreak. Together, the qualitative and quantitative data provided evidence of collective experience and community risk perception across Kenai Peninsula communities. Fire, falling trees, declining quality of watersheds and wildlife habitat, economic fluctuations, landscape change, and emotional loss were some of the issues faced. In some communities, increased timber harvesting brought short-term, positive economic change in the wake of the spruce beetle outbreak. In other communities, the loss of a living spruce (Picea spp.) forest profoundly affected quality of life, and led to community conflict, increased risk perception of future impacts, and economic challenges. Biophysical changes were keenly felt by many residents. Communities at different stages in the spruce beetle outbreak revealed temporal and spatial variations in perceived impacts. The diverse array of perceived impacts and risks from the spruce beetle outbreak in Kenai Peninsula communities presents both opportunities and obstacles for forest management in the context of changing forest conditions.

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Spruce Beetle Outbreaks on the Kenai Peninsula, Alaska, and Kluane National Park and Reserve, Yukon Territory: Relationship to Summer Temperatures and Regional Differences in Disturbance Regimes
When spruce beetles (Dendroctonus rufipennis) thin a forest canopy, surviving trees grow more rapidly for decades until the canopy closes and growth is suppressed through competition. This study used measurements of tree rings to detect such growth releases and reconstruct the history of spruce beetle outbreaks at 23 mature spruce (Picea spp.) forests on and near the Kenai Peninsula, Alaska and four mature white spruce (Picea glauca) forests in Kluane National Park and Reserve, Yukon Territory. On the Kenai Peninsula, all stands showed evidence of 1–5 thinning events with thinning occurring across several stands during the 1810s, 1850s, 1870–1880s, 1910s, and 1970–1980s, which was interpreted as regional spruce beetle outbreaks. However, in the Kluane region, evidence of substantial thinning was only found in one stand from 1934 to 1942 and thinning was only detected across stands during this same time period. Over the last 250 years, spruce beetle outbreaks occurred commonly among spruce forests on the Kenai Peninsula, at a mean return interval of 52 years, and rarely among spruce forests in the Kluane region where cold winter temperatures and fire appear to more strongly regulate spruce beetle population size. The massive 1990s outbreaks witnessed in both regions appeared to be related to extremely high summer temperatures. Recent outbreaks on the Kenai Peninsula (1971–1996) were positively associated with the 5-year backwards running average of summer temperature. It is suggested that warm temperature influences spruce beetle population size through a combination of increased overwinter survival, a doubling of the maturation rate from 2 years to 1 year, and regional drought-induced stress of mature host trees. However, this relationship decoupled after 1996, presumably because spruce beetles had killed most of the susceptible mature spruce in the region. Thus sufficient numbers of mature spruce are needed in order for warm summer temperatures to trigger outbreaks on a regional scale. Following the sequential and large outbreaks of the 1850s, 1870–1880s, and 1910s, spruce beetle outbreaks did not occur widely again until the 1970s. This suggests that it may take decades before spruce forests on the Kenai Peninsula mature following the 1990s outbreak and again become susceptible to another large spruce beetle outbreak. However, if the recent warming trend continues, endemic levels of spruce beetles will likely be high enough to perennially thin the forests as soon as the trees reach susceptible size.

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Vegetation Change and Forest Regeneration on the Kenai Peninsula Following a Spruce Beetle Outbreak, 1987-2000
Forests of the Kenai Peninsula, Alaska experienced widespread spruce (Picea spp.) mortality during a massive spruce beetle (Dendroctonus rufipennis) infestation over a 15-year period. In 1987, and again in 2000, the U.S. Forest Service, Pacific Northwest Research Station, Forest inventory and Analysis Program conducted initial and remeasurement inventories of forest vegetation to assess the broad-scale impacts of this infestation. Analysis of vegetation composition was conducted with indirect gradient analysis using nonmetric multidimensional scaling to determine the overall pattern of vegetation change resulting from the infestation and to evaluate the effect of vegetation change on forest regeneration. For the latter, the impact of the grass bluejoint (Calamagrostis canadensis) on white spruce (Picea glauca) and paper birch (Betula papyrifera) regeneration was specifically assessed. Changes in vegetation composition varied both in magnitude and direction among geographic regions of the Kenai Peninsula. Forests of the southern Kenai Lowland showed the most marked change in composition indicated by relatively large distances between 1987 and 2000 measurements in ordination space. Specific changes included high white spruce mortality (87% reduction in basal area of white spruce >12.7 cm diameter-at-breast height (dbh)) and increased cover of early successional species such as bluejoint and fireweed (Chamerion angustifolium). Forests of the Kenai Mountains showed a different directional change in composition characterized by moderate white spruce mortality (46% reduction) and increased cover of late-successional mountain hemlock (Tsuga mertensiana). Forests of the Gulf Coast and northern Kenai Lowland had lower levels of spruce mortality (22% reduction of Sitka spruce (Picea sitchensis) and 28% reduction of white spruce, respectively) and did not show consistent directional changes in vegetation composition. Bluejoint increased by =10% in cover on 12 of 33 vegetation plots on the southern Kenai Lowland but did not increase by these amounts on the 82 plots sampled elsewhere on the Kenai Peninsula. Across the Kenai Lowland, however, regeneration of white spruce and paper birch did not change in response to the outbreak or related increases in bluejoint cover from 1987 to 2000. Although some infested areas will be slow to reforest owing to few trees and no seedlings, no evidence of widespread reductions in regeneration was found following the massive spruce beetle infestation.

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Effects of Spruce Beetle Infestations on Berry Productivity on the Kenai Peninsula
Understanding the dynamics of berry productivity provides significant insight for managing the landscape to maintain ecosystem functions. On the Kenai Peninsula, as many as 14 mammal and 30 bird species commonly feed on berries produced by shrubs and forbs associated with spruce forests. Brown bears (Ursus arctos) and black bears (Ursus americanus), in particular, rely on berry crops for foraging. Gathering berries for subsistence or recreation purposes is also important to local residents and visitors. Recent spruce beetle (Dendroctonus rufipennis Kirby) infestations on the Kenai Peninsula have altered the dynamics of berry productivity. To assess this relationship, the number and productivity of berries were evaluated with the following environmental covariates: canopy cover, overstory type, infestation level, year of infestation, land type, and land type association. Data were sufficient to describe the relationships of these variables with the productivity of bunchberry dogwood (Cornus canadensis), black crowberry (Empetrum nigrum), false toadflax (Geocaulon lividum), strawberryleaf raspberry (Rubus pedatus), lingonberry (Vaccinium vitis-idaea), and a combination of 24 other species. This was accomplished using log-linear regression by which the variance was estimated using the negative binomial distribution. Canopy cover significantly influenced the productivity of all berry species except for false toadflax. Increasing canopy cover had a negative effect on berry productivity except for strawberryleaf raspberry. Overstory type influenced the productivity of all individual berry species. Infestation level was significantly related to the productivity of black crowberry, false toadflax, and the combined species group. Berry counts were generally lower in plots with low or medium infestation than in plots with high infestation. Relating the dynamics of berry productivity to the effects of spruce beetle infestations provides the opportunity for better management of post-beetle-infested forests.

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Stand and Landscape Level Effects of a Major Outbreak of Spruce Beetles on Forest Vegetation in the Copper River Basin
From 1989 to 2003, a widespread outbreak of spruce beetles (Dendroctonus rufipennis) in the Copper River Basin, Alaska, infested over 275,000 ha of forests in the region. During 1997 and 1998, forest vegetation structure and composition were measured on one hundred and thirty-six 20-m Χ 20-m plots to assess both the immediate stand and landscape level effects of the spruce beetle infestation. A photo-interpreted vegetation and infestation map was produced using color-infrared aerial photography at a scale of 1:40,000. Linear regression was used to quantify the effects of the outbreak on forest structure and composition. White spruce (Picea glauca) canopy cover and basal area of medium-to-large trees [=15 cm diameter-at-breast height (1.3 m, dbh)] were reduced linearly as the number of trees attacked by spruce beetles increased. Black spruce (Picea mariana) and small diameter white spruce (<15 cm dbh) were infrequently attacked and killed by spruce beetles. This selective attack of mature white spruce reduced structural complexity of stands to earlier stages of succession and caused mixed tree species stands to lose their white spruce and become more homogeneous in overstory composition. Using the resulting regressions, a transition matrix was developed to describe changes in vegetation types under varying levels of spruce beetle infestations, and applied the model to the vegetation map. Prior to the outbreak, the study area was composed primarily of stands of mixed white and black spruce (29% of area) and pure white spruce (25%). However, the selective attack on white spruce caused many of these stands to transition to black spruce dominated stands (73% increase in area) or shrublands (26% increase in area). The post-infestation landscape was thereby composed of more even distributions of shrubland and white, black, and mixed spruce communities (17–22% of study area). Changes in the cover and composition of understory vegetation were less evident in this study. However, stands with the highest mortality due to spruce beetles had the lowest densities of white spruce seedlings suggesting a longer forest regeneration time without an increase in seedling germination, growth, or survival.

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Managing Forests Infested by Spruce Beetles in South-Central Alaska: Effects on Nitrogen Availability, Understory Biomass, and Spruce Regeneration
In Alaska, an outbreak of spruce beetles (Dendroctonus rufipennis) recently infested over one million hectares of spruce (Picea spp.) forest. As a result, land management agencies have applied different treatments to infested forests to minimize fire hazard and economic loss and facilitate forest regeneration. In this study, effects of the following treatments were investigated: high-intensity burning, whole-tree harvest, whole-tree harvest with nitrogen (N) fertilization, and conventional harvest of beetle-killed stands 4 years after treatment, as well as clear-cut salvage harvest 6 years after treatment. Available soil ammonium and nitrate were measured and estimated N loss from leaching using in situ cation and anion resin exchange capsules. Spruce regeneration and responses of understory plant species were also assessed. Availability and losses of N did not differ among any of the management treatments. Even a substantial application of N fertilizer had no effect on N availability. Spruce regeneration significantly increased after high-intensity prescribed burning, with the number of seedlings averaging 8.9 m-2 in burn plots, as compared to 0.1 m-2 in plots that did not receive treatment. Biomass of the pervasive grass bluejoint (Calamagrostis canadensis) was significantly reduced by burning, with burn plots having 9.5% of the C. canadensis biomass of plots that did not receive treatment. N fertilization doubled C. canadensis biomass, suggesting that N fertilization without accompanying measures to control C. canadensis is the least viable method for promoting rapid spruce regeneration.

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Fire History of White and Lutz Spruce Forests on the Kenai Peninsula Over the Last Two Millennia as Determined from Soil Charcoal
The presence of over 429,000 ha of forest with spruce (Picea spp.) recently killed by spruce beetles (Dendroctonus rufipennis) on the Kenai Peninsula has raised the specter of catastrophic wildfire. Dendrochronological evidence indicated that spruce beetle outbreaks occurred on average every 50 years in these forests. 121 radiocarbon-dated soil charcoal samples were collected from throw mounds of recently blown over trees to reconstruct the regional fire history for the last ca. 2500 years and no relation was found between fire activity and past spruce beetle outbreaks. Soil charcoal data suggest that upland forests of white (Picea glauca) and Lutz (Picea x lutzii) spruce have not on average burned for 600 years (time-since-fire range 90 to 1500 years, at 22 sites) and that the mean fire interval was 400–600 years. It would thus appear that 10 or more spruce beetle outbreaks can occur for every cycle of fire in these forests. It is cautioned, however, that a trend of warmer summers coupled with an increasing human population and associated sources of ignitions may create a greater fire risk in all fuel types than was present during the time period covered by our study. It is suggested that forest management focus on creating fuel breaks between valued human infrastructure and all types of forest fuels, both green and dead.

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Comments/suggestions?Last updated: 12/19/2006
FIREHouse is a collaboration between the Fire and Environmental Research Applications Team (FERA) of the USDA Forest Service Pacific Northwest Research Station, Pacific Wildland Fire Sciences Laboratory; the University of Washington; the National Park Service; the Bureau of Land Management – Alaska Fire Service; the US Fish and Wildlife Service; and the National Biological Information Infrastructure (NBII). The NBII is a broad, collaborative program that provides increased access to data and information on the nation’s biological resources. Funding for FIREHouse has been provided by the Joint Fire Science Program (JFSP) and NBII. FIREHouse is coordinating efforts with the Fire Research and Management Exchange System (FRAMES) project team. Content on FIREHouse will provide substantial contributions to the Northwest Fire Science Portal and the Alaska Fire Science Portal.
 
Joint Fire Science Program (JFSP) Fire and Environmental Research Applications Team, Pacific Wildland Fire Sciences Laboratory, PNW Research Station, USDA Forest Service, Seattle, WA USDA Forest Service Fire Research and Management Exchange System (FRAMES)    National Biological Information Infrastructure
College of Forest Resources, University of Washington, Seattle, WA
National Park Service Alaska Fire Service US Fish & Wildlife Service