Snow Avalanche Disturbance in Intermountain Spruce-Fir Forests and Implications for the Spruce Bark Beetle (Coleoptera: Scolytidae)

Spruce beetle outbreaks are the primary biotic disturbance affecting forests in the Intermountain spruce-fir zone. Major snow avalanches can produce large quantities of host material for spruce beetle colonization; however, few studies have examined the influence of avalanche disturbance on outbreak initiation. The purpose of my research was to investigate potential relationships between these two disturbance agents. In the first study, I used dendro-ecological analyses to date major avalanche years on the Wasatch Plateau in south-central Utah, and then determined what climate factors were associated with avalanche occurrence. The results indicated that mean January snowfall was significantly related to the probability of major avalanche years, although model correlations were extremely low. Potential dating errors, the lack of complete historical climate data, and the absence of snow pack information may have prohibited obtaining higher model correlations. In the second study, I investigated how the seasonal availability of host material al influenced spruce beetle brood production. I found that significantly fewer mean numbers of spruce beetles were produced in downed spruce felled during August 1997 than from trees felled in April of 1998. More brood adults also were present in, or emerged from the bottom surfaces of sample trees than either unexposed (North, East) or exposed (South, West) bole aspects. These results provided evidence that with greater potential for spruce beetle populations to build in host material produced in the spring, snow avalanche disturbance could contribute to the risk of outbreaks. I constructed snow avalanche and spruce beetle outbreak chronologies from historic documents in the third study, and used classification tree analysis to predict historic spruce beetle outbreaks from major avalanche years and historic climate data. Major snow avalanche years were not identified in this analysis as important for the occurrence of spruce beetle outbreaks. Historic spruce beetle outbreaks, however, were significantly related to generally warm fall and winter temperatures and to drought. These results indicate that climate and other factor not considered in this analysis have a greater influence on spruce beetle epidemiology than the production of host material by snow avalanches

Associations of Armillaria Root Disease in Jack Pine with \u3ci\u3eArceuthobium Americanum\u3c/i\u3e

Relationships between jack pine dwarf mistletoe (Arceuthobium americanum Nutt. ex Engelm.) and Armillaria root disease (Armillaria ostoyae (Romagn.) Herink) were examined to determine how these two disease agents contribute to jack pine (Pinus banksiana Lamb.) decline and mortality in the Belair Provincial Forest, Manitoba, Canada. The incidence and extent of Armillaria root disease was strongly related to tree vigor. Dwarf mistletoe infection did not affect either the incidence of Armillaria or the mean percentage of root system colonization within vigorous, declining, and dead classes of trees. However, field observations and other analyses indicate that dwarf mistletoe was primary responsible for jack pine decline and mortality. In dwarf mistletoe mortality centers, Armillaria appeared to act opportunistically, extensively colonizing only the stressed trees. Analysis of distributions of percent Armillaria colonization revealed that rapid root system colonization occurred just prior to, or at the time of tree death

Influence of Fallen Tree Timing on Spruce Beetle Brood Production

This study compared brood production of the spruce beetle (Dendroctonus rufipennis Kirby [Coleoptera: Curculionidae, Scolytinae]) in downed host material felled during summer and spring seasons on the Wasatch Plateau in south central Utah. Thirty-three matched pairs of Engelmann spruce (Picea engelmannii Parry ex Engelm.) trees were selected for study in spring 1996. One tree of each pair was cut during August 1996 (summer-felled), and the other tree was cut in early April 1997 (spring-felled), so that trees would be colonized by spruce beetles of the same flight period. Brood adults were collected and counted from bark samples, which were removed from the top, bottom, and sides of all sample trees in October 1998. The number of emergent adults produced in June 1999 was determined from exit holes counted in bark samples removed from these same locations. Mixed-model procedures were used to compare differences in the mean number of adults produced in summer-felled versus spring-felled trees in each year. The results indicated that significantly fewer spruce beetles were produced in summer-felled trees than in spring-felled trees. More brood adults were also present in, or emerged from, unexposed bole aspects (bottom, north, and east) of sample trees than exposed aspects (top, south, and west). These findings suggest that disturbances providing spruce beetles with an abundance of fresh host material in the spring result in the greatest potential for spruce beetle production, particularly beneath unexposed bark aspects. Examples of such disturbances include snow avalanches, blowdown, and snow and ice damage

Disturbance Agents and Their Associated Effects on the Health of Interior Douglas-Fir Forests in the Central Rocky Mountains

Interior Douglas-fir is a prevalent forest type throughout the central Rocky Mountains. Past management actions, specifically fire suppression, have led to an expansion of this forest type. Although Douglas-fir forests cover a broad geographic range, few studies have described the interactive effects of various disturbance agents on forest health conditions. In this paper, we review pertinent literature describing the roles, linkages, and mechanisms by which disturbances, including insect outbreaks, pathogens, fire, and other abiotic factors, affect the development, structure, and distribution of interior montane forests primarily comprised of Douglas-fir. We also discuss how these effects may influence important resource values such as water, biodiversity, wildlife habitat, timber, and recreation. Finally, we identify gaps where further research may increase our understanding of these disturbance agents, their interacting roles, and how they influence long-term forest health

Snow Avalanche Disturbance in Intermountain Spruce-fir Forests and Implications for the Spruce Bark Beetle (Coleoptera : Scolytidae)

Spruce beetle outbreaks are the primary biotic disturbance affecting forests in the Intermountain spruce-fir zone. Major snow avalanches can produce large quantities of host material for spruce beetle colonization; however, few studies have examined the influence of avalanche disturbance on outbreak initiation. The purpose of my research was to investigate potential relationships between these two disturbance agents. In the first study, I used dendro-ecological analyses to date major avalanche years on the Wasatch Plateau in south-central Utah, and then determined what climate factors were associated with avalanche occurrence. The results indicated that mean January snowfall was significantly related to the probability of major avalanche years, although model correlations were extremely low. Potential dating errors, the lack of complete historical climate data, and the absence of snow pack information may have prohibited obtaining high model correlations. In the second study, Investigated how the seasonal availability of host material influenced spruce beetle brood production. I found that significantly fewer mean numbers of spruce beetles were produced in downed spruce felled during August 1997 than from trees felled in April of 1998. More brood adults also were present in, or emerged from the bottom surfaces of sample trees than either unexposed (North, East) or exposed (South, West) bole aspects. These results provided evidence that with greater potential for spruce beetle populations to build in host material produced in the host material produced in the spring, snow avalanche disturbance could contribute to the risk of outbreaks. I constructed snow avalanche and spruce beetle outbreak chronologies from historic documents in the third study, and used classification tree analysis to predict historic spruce beetle outbreaks form manor avalanche years and historic climate data. Major snow avalanche years were not identified in this analysis as important for the occurrence of spruce beetle outbreaks. Historic spruce beetle outbreaks, however, were significantly related to generally warm fall and winter temperatures and the drought. There results indicate that climate and other factors not considered in this analysis have a greater influence on spruce beetle epidemiology than the production of host material by snow avalanches

Climate Factors Associated with Historic Spruce Beetle (Coleoptera: Curculionidae) Outbreaks in Utah and Colorado

This study investigated relationships between climate and historic spruce beetle, Dendroctonus rufipennis Kirby (Coleoptera: Curculionidae), outbreaks in northern and southeastern Utah and western Colorado between 1905 and 1996. A chronology of outbreak years was constructed from historic records, research papers, newspapers, and other sources of information. Historic climate data for the region included annual and mean monthly temperature and precipitation, in addition to Palmer drought severity index (PDSI) values estimated from tree rings. Classification and regression tree analysis (CART) was used to identify those climate factors most important for predicting historic spruce beetle outbreaks. The factors identified by the best CART model included mean December temperature, mean September temperature 1 yr before outbreak years, the mean estimated PDSI value of the 5-yr period before outbreak years, and mean October precipitation. The resulting model correctly classified nonoutbreak and outbreak years 67 and 70% of the time, respectively

Postfire Succession and Disturbance Interactions on an Intermountain Subalpine Spruce-Fir Forest

Four general post fire successional pathways leading to a climax Engelmann spruce (Picea engelmannii Parry) subalpine fire (Abies lasiocarpa [Hook] Nutt.) forest operate on the T.W. Daniel Experimental Forest in northern Utah. Depending on the successional pathway followed, reestablishment of the prefire climax will take 200 to 400 years or more due to a rarity of extreme burning conditions. During the long period between catastrophic stand-replacing fires, a variety of other natural disturbances contribute to the varying structure and composition of vegetation and the fuel mosaic in intermountain subalpine spruce-fir forests. Disturbances may range from chronic and small scale to acute and catastrophic, resulting in a broad range of vegetative responses. In addition to crown fires, other major abiotic disturbances (I.E. landslides, mudflows, severe soil erosion, snow avalanche) and biotic disturbances (i.e. disease and insect outbreaks) control the availability of sites for the initiation of new stands of accelerated growth of understory plants and subcanopy trees. Understanding the role of natural disturbance in forest ecosystems is key to managing long-return interval fire regimes. This paper explains how the disturbance regime operating in a given landscape influences vegetative dynamics and fuel mosaics and how the state of the vegetation in turn influences these natural disturbance agents. Managers must recognize biotic and abiotic agents of disturbance and their interactions to fully understand fire regimes and the effects of fire suppression and prescribed fire

Fuels and Fire Behavior Dynamics in Bark Beetle-attacked forests in Western North America and Implications for Fire Management

Declining forest health attributed to associations between extensive bark beetle-caused tree mortality, accumulations of hazardous fuels, wildfire, and climate change have catalyzed changes in forest health and wildfire protection policies of land management agencies. These changes subsequently prompted research to investigate the extent to which bark beetle-altered fuel complexes affect fire behavior. Although not yet rigorously quantified, the results of the investigations, in addition to a growing body of operational experience, indicate that predictable changes in surface, ladder and canopy fuel character- istics do occur over the course of a bark beetle rotation. Input of these changes in fuel characteristics into conventional fire behavior modeling systems can readily provide predictions of potential fire behavior, including the likelihood of crowning. However, several factors limit the direct application of these mod- eling systems in their current form and consequently, they may largely under predict fire potential in such stands. This presents a concern where extreme fire behavior involving both crowning and spotting coupled with flammable fuel conditions can pose serious challenges to incident management and threa- ten the safety of firefighters and the general public alike. In this paper, we review the nature and char- acteristics of bark beetle-altered fuel complexes in the conifer forests of the Interior West and the challenges of understanding the effects on extreme fire behavior, including the initiation and spread of crown fires. We also discuss how emerging fire management plans in the U.S. have begun to integrate wildfire management and other forest health objectives with the specific goal of achieving biodiversity and ecosystem resiliency while simultaneously reducing the existence of hazardous fuel complexes