Allan L. Carroll

Mountain pine beetle and forest carbon feedback to climate change

The mountain pine beetle (Dendroctonus ponderosae Hopkins, Coleoptera: Curculionidae, Scolytinae) is a native insect of the pine forests of western North America, and its populations periodically erupt into large-scale outbreaks. During outbreaks, the resulting widespread tree mortality reduces forest carbon uptake and increases future emissions from the decay of killed trees. The impacts of insects on forest carbon dynamics, however, are generally ignored in large-scale modelling analyses. The current outbreak in British Columbia, Canada, is an order of magnitude larger in area and severity than all previous recorded outbreaks. Here we estimate that the cumulative impact of the beetle outbreak in the affected region during 2000–2020 will be 270 megatonnes (Mt) carbon (or 36 g carbon m-2 yr-1 on average over 374,000 km2 of forest). This impact converted the forest from a small net carbon sink to a large net carbon source both during and immediately after the outbreak. In the worst year, the impacts resulting from the beetle outbreak in British Columbia were equivalent to ∼75% of the average annual direct forest fire emissions from all of Canada during 1959–1999. The resulting reduction in net primary production was of similar magnitude to increases observed during the 1980s and 1990s as a result of global change. Climate change has contributed to the unprecedented extent and severity of this outbreak. Insect outbreaks such as this represent an important mechanism by which climate change may undermine the ability of northern forests to take up and store atmospheric carbon, and such impacts should be accounted for in large-scale modelling analyses.

Cross-scale Drivers of Natural Disturbances Prone to Anthropogenic Amplification: The Dynamics of Bark Beetle Eruptions

ABSTRACT Biome-scale disturbances by eruptive herbivores provide valuable insights into species interactions, ecosystem function, and impacts of global change. We present a conceptual framework using one system as a model, emphasizing interactions across levels of biological hierarchy and spatiotemporal scales. Bark beetles are major natural disturbance agents in western North American forests. However, recent bark beetle population eruptions have exceeded the frequencies, impacts, and ranges documented during the previous 125 years. Extensive host abundance and susceptibility, concentrated beetle density, favorable weather, optimal symbiotic associations, and escape from natural enemies must occur jointly for beetles to surpass a series of thresholds and exert widespread disturbance. Opposing feedbacks determine qualitatively distinct outcomes at junctures at the biochemical through landscape levels. Eruptions occur when key thresholds are surpassed, prior constraints cease to exert influence, and positive feedbacks amplify across scales. These dynamics are bidirectional, as landscape features influence how lower-scale processes are amplified or buffered. Climate change and reduced habitat heterogeneity increase the likelihood that key thresholds will be exceeded, and may cause fundamental regime shifts. Systems in which endogenous feedbacks can dominate after external forces foster the initial breach of thresholds appear particularly sensitive to anthropogenic perturbations.

Potential for range expansion of mountain pine beetle into the boreal forest of North America.

Abstract The potential for mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae: Scolytinae), to expand its historical range in North America from west of the continental divide into the eastern boreal forest was assessed on the basis of analyses of the effects of climate and weather on brood development and survival, and key aspects of the interaction of mountain pine beetle with its hosts and associated organisms. Variation in climate suitability and high host susceptibility in the boreal forest create a finite risk of establishment and local persistence of low-level mountain pine beetle populations outside their historical range. Eventually, these populations could become widespread and cause epidemic infestations, creating an ecological pathway eastward through the boreal forest. Such infestations would reduce the commercial value of forests and impose an additional disturbance on native ecological systems.

Mountain Pine Beetle Red-Attack Forest Damage Classification Using Stratified Landsat TM Data in British Columbia, Canada

ply of suitable pines is exhausted. Effective management of the The identification and classification of mountain pine beetle, mountain pine beetle is dependent upon rapid and accurate Dentroctonus ponderosa (Hopkins), red-attack damage patterns detection of population stage and trend (i.e., increasing or in a mature lodgepole pine (Pinus contorta) forest located in decreasing). Control or suppression is only feasible for the Fort St. James Forest District, British Columbia, was endemic or incipient populations (e.g., Carroll and Linton, accomplished using 1999 Landsat TM satellite imagery, 1999 2002). Most beetle detection programs involve a traditional mountain pine beetle field and aerial survey point data, and approach based on aerial surveys. In this approach, an observer GIS forest inventory data. Unrelated variance in the observed views the forest canopy in a fixed-wing aircraft and looks for spectral response at mountain pine beetle field and aerial signs of attacked trees, that is, dying trees whose foliage is turnsurvey points was reduced following image stratification with ing from green to red. The boundaries of foliage reddening are the GIS forest inventory data and removal of other factors then mentally averaged and delineated onto a sketch map. uncharacteristic of red-attack damage. Locations of known Ground surveyors are often used to verify the cause of the dismountain pine beetle infestation were used to train a maxi- turbance and assess the severity of forest damage. The drawmum-likelihood algorithm; overall classification accuracy was backs of using these surveying methods are the high operation 73 percent, based on an assessment of 360 independent val- costs and many hours of manpower required. Also, mountain idation points. If local stand variability is reduced prior to pine beetles often spread and colonize new areas before an signature generation, accuracies and map products can be infested area has been completely surveyed by ground or air. useful for those involved in active forest management decision- Mountain pine beetle attacks may first create a pre-visual making regarding mountain pine beetle infestations.

Interactions between size and temperature influence fecundity and longevity of a tortricid moth, Zeiraphera canadensis

Females of Zeiraphera canadensis Mut. & Free., the spruce bud moth, were reared in the laboratory at constant and alternating temperatures, and in an outdoor insectary, to (1) determine the effects of temperature, age and size on several reproductive parameters and, (2) to test the hypothesis that body size-temperature interactions influence longevity and realized fecundity. Egg maturation was linearly related to age and large moths developed eggs at a higher rate than small ones. Mcan lifetime oviposition rate reached a maximum and remained stable at temperatures ≥20° C while the mean lifetime rate of egg maturation increased linearly with temperature, indicating that higher temperatures adversely affect oviposition. The production of nonviable eggs increased with age but also with temperature, suggesting high temperature (≥25° C) reduces egg quality and/or hinders fertilization. The realized fecundity and longevity of females reared under an alternating temperature regime (mean 20° C) was significantly less than that of females reared at constant 20° C. Similar realized fecundity, longevity and mean lifetime oviposition rates for females reared at temperatures alternating between 10 and 25° C (mean 20° C) and those at constant 25° C reflected the inability of females to recover from elevated diurnal temperatures. Longevity was positively related to female body size at constant 15 and 20° C but the relationships were negative for moths exposed to diurnal temperatures equal to or exceeding 25° C. Due to the reduced longevity of large moths at high temperatures, linear regressions between size and realized fecundity were only significant at constant temperatures ≤20° C. At higher temperatures, the size-fecundity relationship became curvilinear as a result of the diminished reproductive output of large individuals. Reduced fecundity and longevity of large females at high temperatures may have been due to elevated internal temperatures of large-bodied moths. Large females in a controlled-environment chamber maintained at 25° C developed an internal temperature excess (i.e. temperature above ambient) of nearly 2° C while small-bodied females exceeded ambient by only 0.3° C. However, when held at 20° C, the temperature excess of large-bodied moths was much less than 1° C and small-bodied females did not differ from ambient. Such interactions between temperature and body size suggest that there should be stabilizing selection toward moderate-sized individuals and may explain the absence of size-related effects on fecundity and longevity previously reported for several other lepidopterans.

Development of an Index of Balsam Fir Vigor by Foliar Spectral Reflectance

The potential to measure indices of forest vigor from foliar spectral reflectance was assessed in a range of balsam fir conditions achieved through stand manipulations. In order of increasing vigor, treatments consisted of root pruning, control, thinning, and thinning in combination with fertilization. Concentrations of chlorophyll and nitrogen increased significantly from the low to high vigor plots, and shoot lengths increased by more than three times. Balsam fir shoots from each treatment were measured for reflectance under laboratory conditions by a portable spectroradiometer with a spectral range from 350 nm to 2500 nm. Reflectance decreased consistently with vigor throughout the spectral region analyzed. Most wavebands showed significant effects of the treatments, with the most significant wavebands in the region of chlorophyll absorption between 500 nm and 740 nm. Foliage age class and sample date also affected reflectance in these wavebands. Reflectance indices, defined as the ratio and normalized difference of the most significant waveband at 711 nm and the least significant waveband at 913 nm, were affected by the treatments (P<0.0001). The normalized difference index correlated strongly with concentrations of chlorophyll a (r2⩾0.75), chlorophyll b (r2⩾0.66), nitrogen (r2⩾0.52), and shoots lengths (r2⩾0.69), thereby comprising a spectral index of balsam fir vigor that integrates several aspects of forest physiological condition.

Detecting mountain pine beetle red attack damage with EO-1 Hyperion moisture indices

The mountain pine beetle (Dendroctonus ponderosae) is the most destructive insect of mature pine forests in western North America. Time series of wetness transformations generated from Landsat imagery have been used to detect mountain pine beetle red attack damage over large areas. With the recent availability of high spatial (QuickBird) and high spectral (Hyperion) resolution satellite sensor imagery, the relationship between spectral moisture indices and levels of red attack damage may be investigated. Six moisture indices were generated from Hyperion data and were compared to the proportion of the Hyperion pixel having red attack damage. Results indicate the Hyperion moisture indices incorporating both the shortwave infrared (SWIR) and near infrared (NIR) regions of the electromagnetic spectrum concurrently, such as the Moisture Stress Index, were significantly correlated to levels of damage (r 2 = 0.51; p = 0.0001). The results corroborate the hypothesis that changes in foliage moisture resulting from mountain pine beetle attack are driving the broad‐scale temporal variation in Landsat derived wetness indices. Furthermore, the results suggest that Hyperion data may be used to map low levels of mountain pine beetle red attack damage over large areas that are not consistently captured with Landsat data.

Differences in the Constitutive Terpene Profile of Lodgepole Pine Across a Geographical Range in British Columbia, and Correlation with Historical Attack by Mountain Pine Beetle

Abstract The mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), is a destructive insect pest in western Nearctic conifer forests. Currently, British Columbia, Canada, is experiencing the largest recorded outbreak of this insect, including areas that historically have had low climatic suitability for it. We analyzed 26 constitutive resin terpenes in phloem samples from British Columbia lodgepole pine (Pinus contorta) populations to test for differential resistance to mountain pine beetle attack, based upon the likelihood of previous exposure to mountain pine beetle. We assessed sampled trees for number of mountain pine beetle attacks, number of pupal chambers, and tree survival the following spring. Significant differences were found when levels of certain terpenes in lodgepole pine populations that had likely experienced substantial mountain pine beetle infestations in the past were compared with those in populations that likely had not experienced large outbreaks of mountain pine beetle. Although we expected southern pine populations to contain more total terpenes than northern populations, owing to higher historical exposure to the beetle, the converse was found. Northern populations generally had higher levels of constitutive terpenes and beetle attack than southern populations. Because several terpenes are kairomones to the mountain pine beetle and also serve as precursors for the synthesis of pheromones, the lower levels of terpenes expressed by lodgepole pines from the historical range of the mountain pine beetle may render them less chemically perceptible to foraging beetles.

Facilitation in bark beetles: endemic mountain pine beetle gets a helping hand

1 Endemic populations of the bark beetle Dendroctonus ponderosae attack weakened lodgepole pine (Pinus contorta var. latifolia) trees that are often previously infested by other bark beetle species, such as Pseudips mexicanus. 2 The effect of interactions on D. ponderosae was assessed by examining host selection and productivity of D. ponderosae in trees containing P. mexicanus and trees infested solely by D. ponderosae. 3 The findings obtained show that D. ponderosae attacked hosts previously occupied by P. mexicanus at greater densities, and offspring emerged earlier compared with hosts infested by D. ponderosae alone. Additionally, D. ponderosae larvae in P. mexicanus‐infested trees were found to require a significantly lower amount of resource to complete development with no loss in size. 4 The presence of P. mexicanus may affect host condition, improving the subcortical environment for endemic D. ponderosae, ultimately aiding in population maintenance at low levels. Hosts in this state should be preferentially attacked by D. ponderosae.

Comparison of lodgepole and jack pine resin chemistry: implications for range expansion by the mountain pine beetle, Dendroctonus ponderosae (Coleoptera: Curculionidae)

The mountain pine beetle, Dendroctonus ponderosae, is a significant pest of lodgepole pine in British Columbia (BC), where it has recently reached an unprecedented outbreak level. Although it is native to western North America, the beetle can now be viewed as a native invasive because for the first time in recorded history it has begun to reproduce in native jack pine stands within the North American boreal forest. The ability of jack pine trees to defend themselves against mass attack and their suitability for brood success will play a major role in the success of this insect in a putatively new geographic range and host. Lodgepole and jack pine were sampled along a transect extending from the beetle’s historic range (central BC) to the newly invaded area east of the Rocky Mountains in north-central Alberta (AB) in Canada for constitutive phloem resin terpene levels. In addition, two populations of lodgepole pine (BC) and one population of jack pine (AB) were sampled for levels of induced phloem terpenes. Phloem resin terpenes were identified and quantified using gas chromatography. Significant differences were found in constitutive levels of terpenes between the two species of pine. Constitutive α-pinene levels – a precursor in the biosynthesis of components of the aggregation and antiaggregation pheromones of mountain pine beetle – were significantly higher in jack pine. However, lower constitutive levels of compounds known to be toxic to bark beetles, e.g., 3-carene, in jack pine suggests that this species could be poorly defended. Differences in wounding-induced responses for phloem accumulation of five major terpenes were found between the two populations of lodgepole pine and between lodgepole and jack pine. The mountain pine beetle will face a different constitutive and induced phloem resin terpene environment when locating and colonizing jack pine in its new geographic range, and this may play a significant role in the ability of the insect to persist in this new host.