Mountain Pine Beetle Epidemics Research Articles

Mountain Pine Beetle Epidemic: An Interplay of Terpenoids in Host Defense and Insect Pheromones.

The mountain pine beetle epidemic has highlighted the complex interactions of bark beetles with conifer host defenses. In these interactions, oleoresin terpenoids and volatiles, produced and released by the host tree, can be both harmful and beneficial to the beetle's success in colonizing a tree and completing its life cycle. The insect spends almost its entire life, from egg to adult, within the bark and phloem of a pine host, exposed to large quantities of complex mixtures of oleoresin terpenoids. Conifer oleoresin comprises mostly monoterpenes and diterpene resin acids as well as many different sesquiterpenes. It functions as a major chemical and physical defense system. However, the insect has evolved host colonization behavior and enzymes for terpenoid metabolism and detoxification that allow it to overcome some of the terpenoid defenses and, importantly, to co-opt pine monoterpenes as cues for host search and as a precursor for its own pheromone system. The insect-associated microbiome also plays a role in the metabolism of conifer terpenoids.

Climatic Correlates of White Pine Blister Rust Infection in Whitebark Pine in the Greater Yellowstone Ecosystem

Whitebark pine, a foundation species at tree line in the Western U.S. and Canada, has declined due to native mountain pine beetle epidemics, wildfire, and white pine blister rust. These declines are concerning for the multitude of ecosystem and human benefits provided by this species. An understanding of the climatic correlates associated with spread is needed to successfully manage impacts from forest pathogens. Since 2000 mountain pine beetles have killed 75% of the mature cone-bearing trees in the Greater Yellowstone Ecosystem, and 40.9% of monitored trees have been infected with white pine blister rust. We identified models of white pine blister rust infection which indicated that an August and September interaction between relative humidity and temperature are better predictors of white pine blister rust infection in whitebark pine than location and site characteristics in the Greater Yellowstone Ecosystem. The climate conditions conducive to white pine blister rust occur throughout the ecosystem, but larger trees in relatively warm and humid conditions were more likely to be infected between 2000 and 2018. We mapped the infection probability over the past two decades to identify coarse-scale patterns of climate conditions associated with white pine blister rust infection in whitebark pine.

Beyond red crowns: complex changes in surface and crown fuels and their interactions 32 years following mountain pine beetle epidemics in south-central Oregon, USA

BackgroundMountain pine beetle (Dendroctonus ponderosae Hopkins; MPB), a bark beetle native to western North America, has caused vast areas of tree mortality over the last several decades. The majority of this mortality has been in lodgepole pine (Pinus contorta Douglas ex Loudon) forests and has heightened concerns over the potential for extreme fire behavior across large landscapes. Although considerable research has emerged concerning influence of MPB on forest fuels, there has been little work in the climax lodgepole pine forests of south-central Oregon, USA. Specifically, we assessed changes in forest structure and crown and surface fuels across a chronosequence of time since mountain pine beetle (TSB) epidemics in south-central Oregon (1979 to 2008).ResultsWe classified four distinct periods in which significant changes occur in fuels: overstory mortality stage (2 to 4 years TSB), standing snag and snag fall stage (5 to 13 years TSB), regeneration stage (14 to 25 years TSB), and overstory recovery stage (26 to 32 years TSB). Multivariate analyses indicated changes in crown fuels and forest structure following MPB epidemics were driven primarily by basal area of live and standing dead trees, canopy bulk density, canopy base height, and canopy height. Substantial declines in canopy bulk density occurred early (2 to 5 yrs) following beetle activity and slowly recovered over time. The pattern of succession of surface fuels following a MPB epidemic was largely determined by changes over time in 10-h, 100-h, and 1000-h fuel loads, in addition to increasing fuel bed depth. The 100-h fuel load increased over the entire 30-year period, while 1000-h fuel load reached an asymptote 14 to 26 years following epidemic initiation. Live woody fuels increased through the initial overstory mortality stage and began to decrease during the overstory recovery stage.ConclusionsOur key findings concerning changing fuels and forest structure following a MPB epidemic in south-central Oregon lodgepole pine forests include: 1-h fuels and litter changed little over time, surface fuel loads changed dramatically between the standing snag and the regeneration stages, lodgepole pine remained dominant, and canopy bulk density was low throughout the chronosequence. These factors point to the perpetuation of a lodgepole pine dominated system with a mixed-severity fire regime well into the future.

The Mountain Pine Beetle Epidemic in the Black Hills, South Dakota: The Consequences of Long Term Fire Policy, Climate Change and the Use of Remote Sensing to Enhance Mitigation

The recent and intense outbreak (first decade of 2000s) of the mountain pine beetle in the Black Hills of South Dakota and Wyoming, which impacted over 33% of the 1.2 million acre (486,000 ha) Black Hills National Forest, illustrates what can occur when forest management practices intersect with natural climatic oscillations and climate change to create the “perfect storm” in a region where the physical environment sets the stage for a plethora of economic activities ranging from extractive industries to tourism. This study evaluates the potential of WorldView-2 satellite imagery for green-attacked tree detection in the ponderosa pine forest of the Black Hills, USA. It also discusses the consequences of long term fire policy and climate change, and the use of remote sensing technology to enhance mitigation. It was found that the near-infrared one (band 7) of WorldView-2 imagery had the highest influence on the green-attack classification. The Random Forest classification produced the best results when transferred to the independent dataset, whereas the Logistic Regression models consistently yielded the highest accuracies when cross-validated with the training data. Lessons learned include: (1) utilizing recent advances in remote sensing technologies, most notably the use of WorldView-2 data, to assist in more effectively implementing mitigation measures during an epidemic, and (2) implementing pre-emptive thinning strategies; both of which can be applied elsewhere in the American West to more effectively blunt or preclude the consequences of a mountain pine beetle outbreak on an existing ponderosa pine forest.

Effects of dwarf mistletoe on stand structure of lodgepole pine forests 21-28 years post-mountain pine beetle epidemic in central Oregon.

Lodgepole pine (Pinus contorta) forests are widely distributed throughout North America and are subject to mountain pine beetle (Dendroctonus ponderosae) epidemics, which have caused mortality over millions of hectares of mature trees in recent decades. Mountain pine beetle is known to influence stand structure, and has the ability to impact many forest processes. Dwarf mistletoe (Arceuthobium americanum) also influences stand structure and occurs frequently in post-mountain pine beetle epidemic lodgepole pine forests. Few studies have incorporated both disturbances simultaneously although they co-occur frequently on the landscape. The aim of this study is to investigate the stand structure of lodgepole pine forests 21–28 years after a mountain pine beetle epidemic with varying levels of dwarf mistletoe infection in the Deschutes National Forest in central Oregon. We compared stand density, stand basal area, canopy volume, proportion of the stand in dominant/codominant, intermediate, and suppressed cohorts, average height and average diameter of each cohort, across the range of dwarf mistletoe ratings to address differences in stand structure. We found strong evidence of a decrease in canopy volume, suppressed cohort height, and dominant/codominant cohort diameter with increasing stand-level dwarf mistletoe rating. There was strong evidence that as dwarf mistletoe rating increases, proportion of the stand in the dominant/codominant cohort decreases while proportion of the stand in the suppressed cohort increases. Structural differences associated with variable dwarf mistletoe severity create heterogeneity in this forest type and may have a significant influence on stand productivity and the resistance and resilience of these stands to future biotic and abiotic disturbances. Our findings show that it is imperative to incorporate dwarf mistletoe when studying stand productivity and ecosystem recovery processes in lodgepole pine forests because of its potential to influence stand structure.

Modeling micro-scale ecological processes and emergent patterns of mountain pine beetle epidemics

Forest insect outbreaks can impose significant tree mortality across vast forested landscapes. The current epidemic of mountain pine beetle, Dendroctonus ponderosae Hopkins, for example, has led to the mortality of pine trees in western Canada and the U.S. spanning tens of millions of hectares. The ecological processes driving mountain pine beetle outbreaks are governed by multiple feedback mechanisms, thresholds, and external constraints that exist along a spatial continuum from individual insect–tree interactions to landscape level change. These components of mountain pine beetle epidemics need to be explicitly parameterized in modeling efforts that aim to predict where insect disturbance will occur in a forest each year and the amount of tree mortality that will ensue as a result. However, do date, minimal efforts exist that examine how local level interactions between beetles and trees translate into broader patterns of tree mortality, and those that do are limited to relatively local scales. In this study, we present an agent-based model that simulates how tree mortality results from the combination of beetle–tree interactions, beetle-to-beetle communication, tree defense to beetle attack, beetle density dynamics, host tree availability, dispersal behavior, and landscape heterogeneity. Our model is tested using data from an area in central British Columbia, Canada, that is near the center of the current outbreak in that region. The model simulates both overall tree mortality and spatial patterns of tree mortality, producing results that are similar to those observed in aerial surveys of tree health. Moving forward, the computational efficiency of our model demonstrates the capability to be applied to large, regional landscapes when implemented with sufficient computing resources.

Radial growth of residual overstory trees and understory saplings after mountain pine beetle attack in central British Columbia

There is uncertainty regarding the timing and rate of radial growth of understory saplings and overstory trees in unsalvaged mountain pine beetle (MPB) attacked lodgepole pine stands following one of the largest MPB epidemics in British Columbia (BC). This study was designed to quantify the radial growth response of understory saplings and residual live overstory trees before and after MPB attack. This information is important to assess management options and future timber supply. In total 91 stands were sampled from different age classes and biogeoclimatic sub-zones of central BC. Radial growth was quantified based on five years of tree ring widths immediately preceding the MPB outbreak and five years after attack. Finally, the ratio of area growth was calculated for each tree to describe the change in tree growth following MPB attack. After the death of larger pine trees, healthy vigorous understory species exhibited increased radial growth (percent mean growth increment: MGI) compared to healthy overstory trees. Generally shade tolerant species demonstrated the greatest radial growth among understory species; whereas shade intolerant species had the best growth response among residual live overstory trees. In understory species, the degree of radial growth increased with increased pine mortality while overstory species were not affected by level of MPB attack. This study indicates that radial growth in residual tree species showed a positive response after MPB caused mortality. This may have implications for initiating management strategies and accurate mid-term timber supply projections for MPB killed stands in central BC.

Population structure and migration pattern of a conifer pathogen,Grosmannia clavigera, as influenced by its symbiont, the mountain pine beetle

We investigated the population structure of Grosmannia clavigera (Gc), a fungal symbiont of the mountain pine beetle (MPB) that plays a crucial role in the establishment and reproductive success of this pathogen. This insect-fungal complex has destroyed over 16 million ha of lodgepole pine forests in Canada, the largest MPB epidemic in recorded history. During this current epidemic, MPB has expanded its range beyond historically recorded boundaries, both northward and eastward, and has now reached the jack pine of Alberta, potentially threatening the Canadian boreal forest. To better understand the dynamics between the beetle and its fungal symbiont, we sampled 19 populations in western North America and genotyped individuals from these populations with eight microsatellite markers. The fungus displayed high haplotype diversity, with over 250 unique haplotypes observed in 335 single spore isolates. Linkage equilibria in 13 of the 19 populations suggested that the fungus reproduces sexually. Bayesian clustering and distance analyses identified four genetic clusters that corresponded to four major geographical regions, which suggested that the epidemic arose from multiple geographical sources. A genetic cluster north of the Rocky Mountains, where the MPB has recently become established, experienced a population bottleneck, probably as a result of the recent range expansion. The two genetic clusters located north and west of the Rocky Mountains contained many fungal isolates admixed from all populations, possibly due to the massive movement of MPB during the epidemic. The general agreement in north-south differentiation of MPB and G. clavigera populations points to the fungal pathogen's dependence on the movement of its insect vector. In addition, the patterns of diversity and the individual assignment tests of the fungal associate suggest that migration across the Rocky Mountains occurred via a northeastern corridor, in accordance with meteorological patterns and observation of MPB movement data. Our results highlight the potential of this pathogen for both expansion and sexual reproduction, and also identify some possible barriers to gene flow. Understanding the ecological and evolutionary dynamics of this fungus-beetle association is important for the modelling and prediction of MPB epidemics.

Evaluating Potential Fire Behavior in Lodgepole Pine-Dominated Forests after a Mountain Pine Beetle Epidemic in North-Central Colorado

Abstract A mountain pine beetle outbreak in Colorado lodgepole pine forests has altered stand and fuel characteristics that affect potential fire behavior. Using the Fire and Fuels Extension to the Forest Vegetation Simulator, potential fire behavior was modeled for uninfested and mountain pine beetle-affected plots 7 years after outbreak initiation and 10 and 80% projected tree fall using measured and projected fuel and stand characteristics. Under 90th percentile weather conditions, uninfested plots exhibited proportionally more crown fire than infested plots. Plots predicted to have crown fire were composed mainly of nonhost conifer species and had a lower and more continuous canopy than infested plots. Where surface fire was predicted to occur, live lodgepole pine was the only conifer present, and plots had significantly lower tree mortality from fire than plots predicted to have crown fire. Mountain pine beetle-induced changes in stand and fuel characteristics resulted in increased intensity of surface fire behavior. Furthermore, with 80% infested tree fall, potential smoke production was predicted to be higher. Tree species composition of stands pre and postbark beetle outbreak is important when identifying mountain pine beetle-caused changes to potential fire behavior.

A dynamic bioeconomic analysis of mountain pine beetle epidemics

In this paper, we develop a bioeconomic model of timber harvesting that includes dynamic interactions between mountain pine beetle (MPB) and a lodgepole pine forest with a disaggregated size structure. The model is used to investigate the consequences of alternative public management strategies on forest dynamics in the presence of MPB outbreaks. Management practices similar to those commonly practiced are shown to increase the severity of MPB cycles. Centrally coordinated forest management can eliminate MPB cycles and lessen the impacts of MPB outbreaks with only small reductions in the long-run stock of adult trees.

A Provincial and Regional Assessment of the Mountain Pine Beetle Epidemic in British Columbia: 1999-2008

Western Canada is currently experiencing an epidemic infestation of mountain pine beetle (Dendroctonus ponderosae Hopkins). In British Columbia, the infestation extends over more than 13 million ha and has resulted in a wide-range of social, economic, and ecological impacts. In this study, we compile the known environmental drivers of the infestation and assess these drivers against the actual outcomes of the infestation to date. To support our investigation, we defined the population at risk to mountain pine beetle attack as the spatial extent of pine in British Columbia (approximately 525,329 km^2 ) and used a range of driver variables known to influence the location and success of beetle infestations (i.e., proportion of pine, climatic factors, and l atitude adjusted elevation) as inputs to a two-step clustering algorithm. We generated 15 cl usters representing unique combinations of these driver variables. Variables that represent resulting conditions or infestation outcomes (i.e., cumulative amount of pine killed, proportion of pine remaining, distance to nearest infestation, or stand susceptibility) were then used to characterize these clusters and to identify areas of the province with similar drivers, but with different infestation conditions and outcomes. When the entire study area is considered, our findings indicate that th e most susceptible areas of pine in British Columbia were attacked by the beetle fi rst and that heretofore uninfested areas with similar conditions were likely sp ared from infestations initially due to their abundance of im mature pine. However, infestations in less optimal areas increased ma rkedly in 2007 and 2008, as the competition for hosts increased. A regional assessment of the clusters (for areas in the north, cen tral, and southern regions of British Columbia) further indicated that the beetles may have opportunities to expand in northern and central areas-depending on short-term climatic conditions. By relating our current understanding of infestation drivers to the 2008 infestation, we were able to identify those areas of the province that are most vulnerable to continued infestation. Our results confirm that mountain pine beetle will likely continue to be the dominant forest health concern in British Columbia for many years to come.

Changes in stand structure in uneven-aged lodgepole pine stands impacted by mountain pine beetle epidemics and fires in central British Columbia

We examined the development of lodgepole pine (Pinus contorta Dougl.) in uneven-aged stands in the Interior Douglasfir (IDF) biogeoclimatic zone of central of British Columbia (B.C.), which are currently undergoing a massive outbreak of the mountain pine beetle (Dendroctonus ponderosae Hopkins; MPB). Using historical ecological approaches, dendrochronology, and stand measurement data, we determined the roles MPB and fire disturbances have played in the ecological processes of lodgepole pine in an Interior Douglas-fir zone. We found that multiple mixed-severity fires created patchy uneven-aged stands dominated by lodgepole pine. Since fire suppression in the 20th century, multiple MPB disturbances have maintained the structural complexity of the stands and favoured regeneration of lodgepole pine in the understory despite the absence of fire, resulting in self-perpetuating multi-age lodgepole pine stands. Analysis of the stand structures remaining after multiple MPB outbreaks showed that, even with high overstory mortality, the sample stands contained several MPB-initiated cohorts, consisting of younger and smaller-diameter lodgepole pine. These surviving lodgepole pine layers, which are less susceptible to beetle, will provide important ecological legacies, and could play an important role in the mid-term timber supply chain. We concluded that, in the absence of fire, the MPB plays a more frequent role in directing stand dynamics and structure in uneven-aged lodgepole pine stands resulting in selfperpetuating complex stands in the central interior. We compared and contrasted these findings with those obtained in “even-aged” lodgepole pine stands, also in the Interior Douglas-fir zone in the southern interior, which were investigated in an earlier study. Key words: lodgepole pine, mountain pine beetle, dendroecology, complex stands, mixed-severity fire regime

Effects of a Severe Mountain Pine Beetle Epidemic in Western Alberta, Canada under Two Forest Management Scenarios

We used a simulation model to investigate possible effects of a severe mountain pine beetle (Dendroctonus ponderosaeHopkins) epidemic under two management scenarios in Alberta, Canada. Our simulated outbreak was based on the current epidemic in British Columbia, which may kill close to 80% of the province's pine volume. Our two management scenarios were conventional harvest and a pine-reduction strategy modeled on a component of Alberta's Mountain Pine Beetle Management Strategy. The pine strategy seeks to reduce the number of susceptible pine stands by 75% over the next 20 years through targeted harvesting by the forest industry. Our simulations showed that the pine strategy could not be effectively implemented, even if the onset of the beetle outbreak was delayed for 20 years. Even though we increased mill capacity by 20% and directed all harvesting to high volume pine stands during the pine strategy's surge cut, the amount of highly susceptible pine was reduced by only 43%. Additional pine volume remained within mixed stands that were not targeted by the pine strategy. When the outbreak occurred in each scenario, sufficient pine remained on the landscape for the beetle to cause the timber supply to collapse. Alternative management approaches and avenues for future research are discussed.

Does a Crisis Matter? Forest Policy Responses to the Mountain Pine Beetle Epidemic in British Columbia

“[a]n epidemic of catastrophic proportions”⋖Larry Pedersen, Chief Forester in 2003, in describing the impact of the outbreak. What factors are responsible for the introduction of new policies (especially those involving substantive change) is a phenomenon that is still poorly understood. Researchers have identified policy windows where a confluence of events, such as a change in government, the emergence of a new issue, and ongoing policy processes, come together to create the opportunity for new policy development. Natural disasters can open such policy windows by drawing attention to an issue and mobilizing political will. Yet at the same time, even if policy windows do open, they may not result in effective policy development. The institutional setting in which such policies are developed also plays a key role. In the case of the Canadian forest sector, the combination of public resources and private capital make policy development especially challenging. Although the scale of the Mountain Pine Beetle epidemic in British Columbia is unprecedented, and will change the nature of the forest resource (and by extension the industry and communities that rely upon it), the policy response has been limited to short‐term measures. Although some policy reform was introduced, policy makers have yet to address the question of whether more fundamental changes are required in order to address the full consequences of the epidemic. La détermination des facteurs responsables de l’introduction de nouvelles politiques (particulièrement celles qui comportent des changements substantiels) demeurent un phénomène mal compris. Des chercheurs ont déterminé des fenêtres d’opportunité politique où divers événements, tels qu’un changement de gouvernement, l’émergence d’une nouvelle préoccupation et des processus politiques continus, convergent pour créer l’occasion d’élaborer de nouvelles politiques. Les catastrophes naturelles peuvent créer ces fenêtres d’opportunité politique en attirant l’attention sur une préoccupation et en mobilisant la volonté politique. Pourtant, même si des fenêtres d’opportunité politique s’ouvrent, elles peuvent ne pas se solder par l’élaboration de politiques efficaces. Le cadre institutionnel dans lequel ces politiques sont élaborées joue aussi un rôle important. Dans le cas du secteur forestier canadien, la combinaison de ressources publiques et de capitaux privés rend l’élaboration de politiques particulièrement délicate. Bien que l’étendue de l’épidémie de dendroctone du pin ponderosa en Colombie‐Britannique soit sans précédent et modifiera la nature de la ressource forestière (et par extension, l’industrie et les collectivités qui en dépendent), la réaction politique s’est limitée à des mesures à court terme. Malgré une certaine réforme des politiques, les décideurs doivent s’interroger sur la nécessité d’apporter ou non des changements fondamentaux supplémentaires pour surmonter les conséquences de l’épidémie.

Cutting Strategies can Reduce Probabilities of Mountain Pine Beetle Epidemics in Lodgepole Pine

Cutting Strategies can Reduce Probabilities of Mountain Pine Beetle Epidemics in Lodgepole Pine