Mountain Pine Beetle

Insects are important forest disturbance agents, and mapping their effects on tree mortality and surface fuels represents a critical research challenge. Although various remote sensing approaches have been developed to monitor insect impacts, most studies have focused on single insect agents or single locations and have not related observed changes to ground-based measurements. This study presents a remote sensing framework to (1) characterize spectral trajectories associated with insect activity of varying duration and severity and (2) relate those trajectories to ground-based measurements of tree mortality and surface fuels in the Cascade Range, Oregon, USA. We leverage a Landsat time series change detection algorithm (LandTrendr), annual forest health aerial detection surveys (ADS), and field measurements to investigate two study landscapes broadly applicable to conifer forests and dominant insect agents of western North America. We distributed 38 plots across multiple forest types (ranging from mesic mixed-conifer to xeric lodgepole pine) and insect agents (defoliator [western spruce budworm] and bark beetle [mountain pine beetle]). Insect effects were evident in the Landsat time series as combinations of both short- and long-duration changes in the Normalized Burn Ratio spectral index. Western spruce budworm trajectories appeared to show a consistent temporal evolution of long-duration spectral decline (loss of vegetation) followed by recovery, whereas mountain pine beetle plots exhibited both short- and long-duration spectral declines and variable recovery rates. Although temporally variable, insect-affected stands generally conformed to four spectral trajectories: short-duration decline then recovery, short- then long-duration decline, long-duration decline, long-duration decline then recovery. When comparing remote sensing data with field measurements of insect impacts, we found that spectral changes were related to cover-based estimates (tree basal area mortality [R2adj=0.40, F1,34=24.76, P<0.0001] and down coarse woody detritus [R2adj=0.29, F1,32=14.72, P=0.0006]). In contrast, ADS changes were related to count-based estimates (e.g., ADS mortality from mountain pine beetle positively correlated with ground-based counts [R2adj=0.37, F1,22=14.71, P=0.0009]). Fine woody detritus and forest floor depth were not well correlated with Landsat- or aerial survey-based change metrics. By characterizing several distinct temporal manifestations of insect activity in conifer forests, this study demonstrates the utility of insect mapping methods that capture a wide range of spectral trajectories. This study also confirms the key role that satellite imagery can play in understanding the interactions among insects, fuels, and wildfire.

The mountain pine beetle epidemic is one of the most devastating insect outbreak since the great locust swarms of the 1870’s and an environmental disaster comparable to the dust bowl of the 1930’s. The typical state of many North American pine forests -- mature, homogeneous, even-aged, and dense -- combine to provide volatile environmental conditions primed for a beetle population explosion.  The unusually warm and dry climate of the past couple decades has fueled the beetle’s reproduction.  The resulting outbreaks have engulfed millions of acres of pine forests from southern California to Alaska.

The aftermath has left billions of dead trees. If the trees are not harvested, they will eventually become a carbon source releasing CO2 back into the air either rapidly through forest fire or slowly through decay.  Canada’s Pacific Forestry Center has conducted studies revealing that the magnitude of the beetle disturbance is great enough to completely reverse the carbon cycle of the forest.  Furthermore, a study from the University of Idaho estimates that infested stands will take a generation to regain their living biomass and the average stand will take over a century for its carbon flux to become a net sink again.  Carbon emissions from forest fires are also expected to dramatically increase in correlation with the beetle-kill.

Limiting the impact of the mountain pine beetles' carbon footprint will require proactive forest management that emphasizes both economic benefit and forest health.  Harvesting beetle-kill trees for lumber, pulp, and other commercial products permanently sequesters the carbon in the wood.  Furthermore, bio-mass from beetle-kill can be utilized for energy production as a substitute for fossil fuels. In a time of high unemployment and recession, this could be at least a short term boom for many existing and new businesses.  Replanting landscapes that are more biologically diverse will reduce the likelihood of future epidemics and simultaneously accelerate the forest’s carbon offset potential.

The aim of our study was to estimate forest vulnerability and potential distribution of three bark beetles
(Curculionidae: Scolytinae) under current and projected climate conditions for 2020 and 2050. Our study
focused on the mountain pine beetle (Dendroctonus ponderosae), western pine beetle (Dendroctonus
brevicomis), and pine engraver (Ips pini). This study was conducted across eight states in the Interior West
of the US covering approximately 2.2 million km2 and encompassing about 95% of the Rocky Mountains
in the contiguous US. Our analyses relied on aerial surveys of bark beetle outbreaks that occurred
between 1991 and 2008. Occurrence points for each species were generated within polygons created
from the aerial surveys. Current and projected climate scenarios were acquired from the WorldClim database
and represented by 19 bioclimatic variables. We used Maxent modeling technique fit with occurrence
points and current climate data to model potential beetle distributions and forest vulnerability.
Three available climate models, each having two emission scenarios, were modeled independently and
results averaged to produce two predictions for 2020 and two predictions for 2050 for each analysis.
Environmental parameters defined by current climate models were then used to predict conditions under
future climate scenarios, and changes in different species’ ranges were calculated. Our results suggested
that the potential distribution for bark beetles under current climate conditions is extensive, which coincides
with infestation trends observed in the last decade. Our results predicted that suitable habitats for
the mountain pine beetle and pine engraver beetle will stabilize or decrease under future climate conditions,
while habitat for the western pine beetle will continue to increase over time. The greatest increase
in habitat area was for the western pine beetle, where one climate model predicted a 27% increase by
2050. In contrast, the predicted habitat of the mountain pine beetle from another climate model suggested
a decrease in habitat areas as great as 46% by 2050. Generally, 2020 and 2050 models that tested
the three climate scenarios independently had similar trends, though one climate scenario for the western
pine beetle produced contrasting results. Ranges for all three species of bark beetles shifted considerably
geographically suggesting that some host species may become more vulnerable to beetle attack in
the future, while others may have a reduced risk over time.

The efficacy of direct control methods in bark beetle outbreaks is a disputed topic. While some studies report that control reduces tree mortality, others see little effect. Existing models, linking control rate to beetle population dynamics and tree infestations, give insights, but there is a need to take into account the environment spatial variability and its impact on beetle life cycle. Here, we use natural variability found in a carefully monitored and controlled infestation to simulate outbreak dynamics under different control effort and to explore the impact of control on outbreaks suppression and tree mortality. Our semi-empirical predictive model of the number of infested trees as a function of ecological and environmental variables is coupled to a simulation model for infestation dynamics. We show that even a little control can have a major impact on the number of infested trees after several years of sustained effort. However, a moderate control of 60% is required to reduce the beetle population on the long term. Furthermore, a control rate of 69%-83% is needed to achieve outbreak suppression in under 13 years depending on the abundance of incoming flights from outside sources.

There are 195 vertebrate species occurring in mountain pine beetle (Dendroctonus ponderosae Hopkins) infested areas in interior British Columbia that will likely be impacted by beetle control measures. The effects of these measures on wildlife will depend on whether they increase or decrease the availability of critical habitat attributes such as large trees, dead and dying trees, down wood, shrubby

The current latitudinal and elevational range of mountain pine beetle is not limited by available hosts. Instead, its potential to expand north and east has been restricted by climatic conditions unfavorable for brood development. We combined a model of the impact of climatic conditions on the establishment and persistence of mountain pine beetle populations with a spatially explicit, climate-driven simulation

We used a simulation model to investigate possible effects of a severe mountain pine beetle (Dendroctonus ponderosae Hopkins) 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...

The infection pattern of a mountain pine beetle (MPB) epidemic in the Black Hills National Forest (BHNF) was extracted from National Agriculture Imagery Program (NAIP) aerial photography data via the application of pixel colour analysis and texture functions. From initial analysis, local percolation clusters were identified. Epidemic simulations were then run varying three variables in parameter space – the probability of an infected tree from a previous year spawning a new percolation cluster the year after, the standard deviation of the distance travelled to form a new cluster, and the number of iterations used to develop each infection cluster. The best simulation parameters, as defined by a numerical similarity factor, produces a model which is significantly better than random results. Further analysis is required to further specify the optimal parameters of the simulation. A more comprehensive exploitation of photographical data for this purpose will require crowdsourcing and machine learning. 2

The current epidemic of mountain pine beetle (Dendroctonus ponderosae Hopkins) in British Columbia, Canada, has impacted an area of over 13 million hectares presenting a considerable challenge to provincial forest resource managers. Remote sensing technologies offer a highly effective tool to monitor this impact due to very large areas involved and its ability to detect dead and dying tree crowns. Conventionally, change detection procedures based upon spectral values have been applied; however, analysis of landscape pattern changes associated with long-time series change detection approaches present opportunities for the generation of unique and ecologically important information. This study is focussed on the detection and monitoring of the shape and area characteristics of lodgepole pine stands during mountain pine beetle infestation to quantify the progression of forest fragmentation and related loss of landscape connectivity. A set of landscape pattern indices were applied to a ...

The mountain pine beetle (Dendroctonus ponderosae Hopk.)(Coleoptera: Scolytidae) is an aggressive bark beetle that periodically increases to outbreak levels killing thousands of trees. It is considered one of the major natural disturbance agents in North ...

Bark beetles that colonize living conifers and their microbial associates encounter constitutive and induced chemical defenses of their host. Monoterpene hydrocarbons comprise a major component of these allelochemicals, and many are antibiotic to insects, fungi, and bacteria. Some bark beetle species exhaust these defenses by killing their host through mass attacks mediated by aggregation pheromones. Others lack adult aggregation pheromones and do not engage in pheromone-mediated mass attacks, but rather have the ability to complete development within live hosts. In the former species, the larvae develop in tissue largely depleted of host terpenes, whereas in the latter exposure to these compounds persists throughout development. A substantial literature exists on how monoterpenes affect bark beetles and their associated fungi, but little is known of how they affect bacteria, which in turn can influence beetle performance in various manners. We tested several bacteria from two bark beetle species for their ability to grow in the presence of a diversity of host monoterpenes. Bacteria were isolated from the mountain pine beetle, Dendroctonus ponderosae Hopkins, which typically kills trees during colonization, and the red turpentine beetle, Dendroctonus valens LeConte, which often lives in their host without causing mortality. Bacteria from D. ponderosae were gram-positive Actinobacteria and Bacilli; one yeast also was tested. Bacteria from D. valens were Actinobacteria, Bacilli, and γ-Proteobacteria. Bacteria from D. valens were more tolerant of monoterpenes than were those from D. ponderosae. Bacteria from D. ponderosae did not grow in the presence of α-pinene and 3-carene, and grew in, but were inhibited by, β-pinene and β-phellandrene. Limonene and myrcene had little inhibitory effect on bacteria from either beetle species. Tolerance to these antibiotic compounds appears to have resulted from adaptation to living in a terpene-rich environment.