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Communications Ecological Applications, 20(4), 2010, pp. 895–902 Ó 2010 by the Ecological Society of America

Whitebark pine vulnerability to climate-driven mountain pine beetle disturbance in the Greater Yellowstone Ecosystem JESSE A. LOGAN,1,4 WILLIAM W. MACFARLANE,2

AND

LOUISA WILLCOX3

1 USDA Forest Service, Box 482, Emigrant, Montana 54927 USA GeoGraphics, Incorporated, 90 West Center Street, Logan, Utah 84321 USA 3 Natural Resources Defense Council, Box 70, Livingston, Montana 59047 USA 2

Abstract. Widespread outbreaks of mountain pine beetles (MPB) are occurring throughout the range of this native insect. Episodic outbreaks are a common occurrence in the beetles’ primary host, lodgepole pine. Current outbreaks, however, are occurring in habitats where outbreaks either did not previously occur or were limited in scale. Herein, we address widespread, ongoing outbreaks in high-elevation, whitebark pine forests of the Greater Yellowstone Ecosystem, where, due to an inhospitable climate, past outbreaks were infrequent and short lived. We address the basic question: are these outbreaks truly unprecedented and a threat to ecosystem continuity? In order to evaluate this question we (1) present evidence that the current outbreak is outside the historic range of variability; (2) examine system resiliency to MPB disturbance based on adaptation to disturbance and host defenses to MPB attack; and (3) investigate the potential domain of attraction to large-scale MPB disturbance based on thermal developmental thresholds, spatial structure of forest types, and the confounding influence of an introduced pathogen. We conclude that the loss of dominant whitebark pine forests, and the ecological services they provide, is likely under continuing climate warming and that new research and strategies are needed to respond to the crisis facing whitebark pine. Key words: climate change; Dendroctonus ponderosae; disturbance ecology; ecological resiliency; global warming; Greater Yellowstone Ecosystem; historic range of variability; lodgepole pine; mountain ecology; Mountain pine beetle; Pinus albacaulis; whitebark pine.

INTRODUCTION Yellowstone National Park looms large in the conservation history of not only the United States but the world in general. As the world’s first national park, Yellowstone has inspired the creation of other parks and natural reserves worldwide; and within the United States, it also played an important role in creation of the National Forest system. The first National Forest (the Shoshone) was established in 1891 abutting the eastern boundary of the Park, and subsequent national forests and protected areas were established in the surrounding region. This collection of national parks, national forests, and wildlife refuges has become collectively known as the Greater Yellowstone Ecosystem (GYE). At approximately 73 000 km2, an area Manuscript received 23 April 2009; revised 24 November 2009; accepted 3 December 2009. Corresponding Editor: A. D. McGuire. 4 E-mail: [email protected]

roughly the size of South Carolina, the GYE is one of the largest nearly intact temperate-zone ecosystems remaining on earth today. Across the GYE, whitebark pine (Pinus albacaulis), an important component of the ecosystem, is facing serious decline. Mountain pine beetle (MPB, Dendroctonus ponderosae) outbreaks are occurring throughout the entire distribution of the GYE whitebark pine (Fig. 1), in some areas resulting in whitebark pine mortality exceeding 95% of cone bearing trees (those greater than approximately 12.7–15.24 cm; Gibson et al. 2008). The mountain pine beetle is somewhat unique, belonging to the relatively small group of ‘‘aggressive’’ bark beetles that must kill their host to successfully reproduce. Eruptive outbreaks of this bark beetle can be impressive events, particularly in its principal host, lodgepole pine (Pinus contorta). Previous research indicated the limitation of mountain pine beetle distribution to the north (Safranyik 1978) and in high elevation forests (Amman 1973) was accounted for by

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FIG. 1. (Left) Looking north from the Bonneville Pass Trailhead, Absaroka Range, Shoshone National Forest, east-central GYE (Greater Yellowstone Ecosystem, USA). (Right) Lazyman Hill, from the Gravelly Range Road, Beaverhead National Forest, northwest GYE. Photos credits: W. W. Macfarlane.

the typically cold temperatures of both habitats. With the advent of a warming climate (1) winter temperatures have become mild enough to allow substantial overwinter survival of all life stages and (2) there is sufficient summer thermal energy to complete an entire life cycle in one year. Historically, the simultaneous occurrence of these necessary conditions in whitebark pine forests occurred only infrequently. With the level of warming that has already occurred (Fig. 2C), their simultaneous occurrence has become common (Fig. 2A, B). Whitebark pine plays a major role in the ecological integrity of the GYE since it functions as both a foundation and a keystone species. It forms the foundation of high mountain and alpine ecosystems (those above approximately 2591 m [8500 feet] in the GYE) by providing the major biomass and primary productivity, enhancing soil formation, and serving as ‘‘nurse trees’’ for other conifers. In the spatial context of the entire GYE, it is a keystone species because of the driving influence of high elevation forests on snow dynamics, both in the distribution of snow during winter and subsequent temporal attenuation of spring melt. The large, fleshy, highly nutritious seeds of whitebark pine also provide critical resources to a wide array of wildlife species ranging from Clark’s Nutcracker (Nucifraga columbiana) and red squirrels (Tamiasciurus hudsonicusto) to the iconic grizzly bear (Ursus arctos). The importance of whitebark pine seeds to the grizzly is of particular importance in the GYE due to paucity of other high quality food during the critical time prior to entering hibernation (Mattson et al. 1992). The potential for a climate change induced shift in thermal habitat that would allow intensified mountain pine beetle activity in high elevation forests was first recognized in modeling studies (Logan and Bentz 1999, Logan and Powell 2001). In particular, the threshold nature of temperature interactions with life-stage specific developmental rates has been mathematically described (Fig. 2D; Logan and Powell 2001, Powell and Logan

2005, Logan and Powell 2009), along with the potential for ecological expression of these thresholds (Logan and Bentz 1999). As noted in Raffa et al. (2008), these climate change precipitated events have increased the likelihood that key thresholds will be exceeded resulting in fundamental regime shifts. Logan and Bentz (1999) suggested that due to the potential for regime shift, increased MPB activity in whitebark pine would be a good candidate for a ‘‘canary in the coal mine’’ indicator for the ecological impacts of climate change. In summary, there is no doubt that a major disturbance event is under way in an important and sensitive ecosystem (Logan et al. 2009). The question of interest, however, is not ‘‘has a major disturbance occurred?’’ but rather, ‘‘how important is this disturbance in an ecological context?’’ In an attempt to answer this question we employ three basic approaches from disturbance ecology within the context of climate change: we first evaluate the current MPB outbreak with respect to the historic range of variability; we then address ecological resiliency through comparison to a system (lodgepole pine) of known resiliency; finally we discuss shifts in three critical factors that have resulted in an altered domain of attraction. HISTORIC RANGE

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The historic range of variability provides a criterion for evaluating the seriousness of a disturbance event by providing a historical context of past events. The basic assumption is that highly unusual disturbances may exceed a system’s capacity for recovery. A variety of techniques, involving both direct and indirect measures, have been used to provide such a framework. In evaluating the historic range of variability in GYE whitebark pine, we consider two pieces of evidence: historical accounts of a widespread mountain pine beetle outbreak during the 1930s, and the ecological legacy of such disturbance in current whitebark pine forests.

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YELLOWSTONE WHITEBARK PINE MORTALITY

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Communications FIG. 2. Driving variable and simulation model results. (A) Annual minimum temperature (Tmin, yearly and 5-year smoothed) and modeled mountain pine beetle proportional survival (P(survival), yearly and 5-year smoothed) for the Togwotee Pass, Wyoming snow telemetry (SNOTEL) site. This is the closest SNOTEL site to the massive mortality that has occurred in the Teton Wilderness. Temperatures were interpolated, and survival was predicted using the model described in Re´gnie`re and Bentz (2007). (B) Model predictions for whitebark pine (WBP) risk to mountain pine beetle over the interval 1980–2020 computed for 30-year weather normals (i.e., 1980–2010 and 1990–2020). Whitebark pine distribution shown in red is predicted to be at high risk (P . 0.5 of adaptive seasonality), while areas of distribution in green are at low risk (P , 0.5 of adaptive seasonality). (C) Mean annual temperatures for the 11 western states with quadratic LowESS smoothed trend-line with 30-year moving window (solid red line); grand mean prior to 1976 (dashed green line); overall grand mean in 1975 (dashed yellow line); and grand mean since 1975 (dashed red line). Note that the mean annual temperature in 1975 was almost exactly that of the overall mean until that point (data are from Kelly Redmond, Western Regional Climate Center, Reno, Nevada, USA). (D) Bifurcation results from Logan and Bentz (1999) and Powell and Logan (2005) for Railroad Ridge, White Cloud mountains, central Idaho. A single plotted point indicates synchronous pine beetle emergence (adaptive), while multiple points indicate complex cycles of emergence (maladaptive). The indicated x-axis value of temperature is the deviation from mean annual temperature obtained by adding the indicated x-axis value to every hourly temperature throughout the year. The first synchronous band, including the observed annual temperature (x-axis value of zero), requires a two-year life cycle (maladaptive), while an increase of a little more than 2.58C in mean annual temperature results in an adaptive synchronous, one-year life cycle (see Logan and Powell [2009] for detailed discussion of bifurcation analysis procedure). Emergence day is the day of the year, with day 1 ¼ 1 January.

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Historic outbreaks in GYE whitebark pine During the 1930s, a widespread mountain pine beetle outbreak occurred across the United States distribution of whitebark pine, including the GYE. This past mortality event has been used to support the view that the current event is within the historical range of variability (Gibson et al. 2008). In particular, in a 1934 report, Chief Ranger George Baggley wrote, ‘‘The mountain pine beetle epidemic is threatening all of the white bark and lodgepole pine stands in Yellowstone Park. Practically every stand of white bark is heavily infested . . . and will be swept clean in a few years [emphasis added] . . .’’ (Evenden 1944 in Furniss and Rankin 2003). The key to Baggley’s observation is the phrase ‘‘will be swept clean in a few years’’: obviously this did not happen, instead the outbreak was relatively short-lived and limited in scale and intensity. However, if we evaluate the underlying driving variable of temperature, we see that the current situation is vastly different from the 1930s. This prior event also resulted from warm temperatures, unusually warm temperatures occurred throughout the west during the 1930s, and in particular the winter of 1933–1934 was the warmest in the historical record. However, this warm period was short lived, and temperatures quickly returned to historical ranges. Something very different is occurring today with global warming. Instead of a short-term weather event, we are experience a climate trend that started in the 1970s or 1980s and continues unabated (Fig. 2C). Mountain pine beetle disturbance legacy in GYE whitebark pine Whitebark pine is an exceptionally slow growing species; in the GYE a tree typically requires a minimum of 50 years to reach cone-bearing age, and in many sites, significantly longer. The slow growth rate of this species combined with the slow decomposition rates of cold, xeric climates of high mountains guarantees that evidence of mountain pine beetle disturbances in whitebark pine will remain on the landscape for decades if not centuries (Perkins and Swetnam 1996). There are large landscapes in the GYE where essentially all the whitebark pine overstory has been killed during the current outbreak episode, and these landscapes are widely distributed across the GYE (Fig. 1). The standing dead trees will eventually weather into massive ‘‘ghost forests’’ that will remain an obvious landscape attribute for many years to come (Furniss and Renkin 2003), spanning a time period greater than that from 1930 to present. With extensive recent on-ground and aerial survey experience, we are unaware of any place in the GYE where ghost forests from the 1930s remotely approach the magnitude of current disturbance events. In a recent editorial describing a visit to one landscape in the GYE (Tomback 2008), Diana Tomback, Director of the Whitebark Pine Ecosystem Foundation, wrote, ‘‘We discovered massive whitebark pines, at least a thousand


years of age, hit this year by mountain pine beetles. Given that they had survived numerous past beetle outbreaks, including those of the 1930s and 1970s, this was a disheartening find.’’ Even more disheartening from an ecological perspective is the complete removal of the reproductive component (cone-bearing tree) of the population over large areas. In conclusion, the scope of whitebark pine mortality in the GYE appears to be well beyond the episodic events of the historical past. ECOLOGICAL RESILIENCY Ecological resilience was first used by C. S. Holling and coworkers at the University of British Columbia to describe the ability of an ecosystem to adsorb disturbance without undergoing fundamental reorganization; ‘‘ecosystem resilience’’ is the capacity of an ecosystem to tolerate disturbance without transitioning into a qualitatively different state that is controlled by a different set of processes. It is axiomatic that surviving ecological systems are resilient or else they would not exist. It is just as true that there are limits to resiliency, and a key contribution of disturbance ecology is to provide a framework for evaluating the degree of resilience of an ecosystem to a specific disturbance. With respect to mountain pine beetle, a useful starting point is to compare outbreaks in lodgepole pine forests (a system known to be highly resilient to mountain pine beetle outbreaks) to whitebark pine ecosystems (a system of unknown resiliency to the scope of present outbreaks). Comparative resiliency to large-scale disturbance Lodgepole pine is a quintessential opportunistic species. The reproductive response to large-scale disturbance such as fire is immediate and spectacular. For example, essentially all the widespread lodgepole forests of the GYE that were ‘‘wiped out’’ (Smith 1995) by the 1988 fires are once again a canopy of luxuriant lodgepole regrowth. The time required to reach cone-bearing age for lodgepole pine is short, typically 5–10 years, and 20 years post fire, many of these stands contain conebearing trees. Lodgepole cones contain an abundance of wind-dispersed seeds in both serotonous and nonserotonous cones, resulting in an abundant reserve of seeds in the tightly closed serotonous cones that remain viable on the trees for years. If lodgepole pine is the quintessential opportunistic species, then whitebark pine provides the quintessential counterpoint. Time required to reach cone-baring age is long, typically a minimum of 50 years (McCaughey and Schmidt 1990). Compared to lodgepole pine, whitebark pine seeds are large and relatively few in number, requiring an individually greater investment in energy and resources to produce each seed. Furthermore, the abundant seeds of lodgepole are wind dispersed (once cones are opened) compared to the relative fewer seeds of whitebark which are dependent on Clark’s Nutcracker for dispersal. These seeds are such a valuable food resource to wildlife consumers that few seeds not

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Host defenses An essential component of lodgepole pine ecosystem resiliency to mountain pine beetle outbreaks results from effective chemical defenses of individual trees to beetle attack. Chemical defenses involve both a primary or constitutive, and a secondary or induced, resin capacity. The primary resin capacity serves to physically incapacitate and/or expel attacking beetles as they sever resin ducts while boring through the bark. The constitutive response is characterized by conspicuous pitch tubes formed at the sites of attacking beetles. The induced resin capacity is mobilized in response to attacking beetles and involves the breakdown of parenchyma cells that serve to encapsulate attacking beetles, and also increased production of monoterpene and phenolic compounds that are toxic to the beetle (Raffa et al. 2008). Evidence of a successful induced response is an obvious lesion of stained tissue surrounding the dead beetle. In lodgepole pine, both responses are obvious, even to the untrained observer. The resin response of whitebark pine to attacking beetles has consistently been less obvious than that in lodgepole pine. Whitebark does not typically produce the copious pitch tubes of lodgepole, and the cryptic evidence of mass-attacked trees is often difficult to detect, even for an experienced observer. Although not unknown (E. Campbell, personal communication; J. A. Logan, personal observation), evidence of an induced response is rare in whitebark pine, as are trees with successful ‘‘pitch outs’’ (‘‘pitch out’’ refers to a beetle attack that has successfully been repulsed by the tree). The name refers to the resulting conspicuous pitch tube that remains on lodgepole pine trees, often containing

the attacking beetle. Although specific research on the characteristic of whitebark pine chemical defenses is in its infancy, preliminary research suggests differences in chemical composition for both primary and secondary resins (K. F. Raffa, personal communication). Vulnerability to attacking beetles has important direct and indirect consequences for resiliency. In addition to chemical defenses, other confounding factors like interactions with fungal associates (Bleiker and Six 2009) may play a role in whitebark’s greater vulnerability to attacking beetles. For whatever reasons, whitebark pine appears to be more vulnerable to attacking beetles than the coevolved lodgepole pine. Even low attack densities result in successful establishment of the beetle, killing the tree (or at least a portion of it), and successful strip attacks (where only a portion or strip of the bole is killed) are commonly observed. Warming temperatures since the 1970–1980s combined with vulnerability to attacking beetles has combined to produce a worst-case scenario. We have consistently observed large numbers of successfully attacked trees in late spring/early summer. Apparently, re-emerging parent adults from the previous summer, perhaps augmented by an early phase emergence of new brood adults, are responsible for this mortality (Bentz and Schen-Langenheim 2007). Winters are becoming mild enough that even adult beetles, a freeze intolerant stage, are surviving (Fig. 2A). These surviving beetles, at even relatively low densities, have been able to successfully attack new whitebark pine trees. Strip attacks, in which only a portion of the tree’s phloem tissue is killed, have been more commonly observed than in lodgepole. Brood produced by re-emerged adults may experience enough thermal energy to complete the life cycle within the same year of attack (J. A. Logan, unpublished data). Even if this early brood does not reach the adult stage, all life stages, even those previously susceptible to winter mortality, are surviving. The result is a bi-peak emergence of early, re-emerged beetles and a later traditionally timed brood. The combination of a warming climate and apparent vulnerability to attacking beetles has resulted in a shift from nonoverlapping, semivoltine (life cycle requiring two years to complete) generations to overlapping, bimodal, univoltine generations with a concomitant increase in reproductive potential. DOMAIN

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The domain of attraction is a concept closely related to resilience that defines the ecological limits of how far a system can be disturbed without shifting to a new regime. Climate change has reduced the domain of attraction for GYE whitebark pine in three ways: (1) by exceeding the temperature threshold for adaptive seasonality (a seasonal temperature cycle that results in the three conditions of a strictly univoltine life cycle, synchronous adult emergence, and emergence at an appropriate time of year; Logan and Powell 2001, 2009);

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protected in neglected nutcracker caches go unutilized. Essentially the entire reproductive strategy of whitebark pine is dependent on residual seeds from Clark’s Nutcracker caches (McKinney et al. 2009). While this mutualistic relationship has served whitebark well in past disturbance regimes, it is not particularly well adapted to the current large scale, climate change driven disturbance. The tree–bird relationship is asymmetric, with the tree being more dependent on the bird than the bird on the tree. There is a threshold of cone/seed density below which the opportunistic Nutcracker will seek alternative food sources (McKinney et al. 2009). If cone bearing overstory trees are removed by mountain pine beetles over large contiguous areas, then the opportunity for whitebark pine recruitment will plummet. Fire and snow avalanches are ubiquitous disturbances in high mountain environments. In historical times, Clark’s Nutcrackers effectively replanted whitebark in openings resulting from these disturbances. A reasonable conjecture if cone densities fall below that required to attract and maintain Clark’s Nutcrackers is that this previously successful strategy will become increasingly unlikely for both disturbances.

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(2) through a spatial shift in the climatic isolation of whitebark pine from other historic host pine species; and (3) by providing a synergistic interaction between mountain pine beetle and white pine blister rust (WPBR, Cronartium ribicola) that exacerbates the impact of the beetle. Direct threshold on MPB population ecology

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The limits to the domain of attractions are often defined by threshold events (Walker and Salt 2006). Landscape level simulations indicated that much of the GYE whitebark pine was at high risk under reasonable climate change scenarios due to seasonal temperatures resulting in dynamics that exceeded the threshold for adaptive seasonality (Logan and Powell 2009). Subsequent events have evolved qualitatively similar to model predictions, with the highest mortality first occurring on the northwest portion of the GYE and proceeding generally to the east. Model predictions also indicated that some areas were more resistant to climate warming than others, namely the central core of the Wind River Range in Wyoming and the Beartooth Plateau in Montana. Subsequent ground surveys have confirmed these predictions. An alternative host for the mountain pine beetle in close approximation to whitebark pine A common situation over much of the U.S. Rocky Mountains is for lodgepole or ponderosa pine to occupy lower elevations, non-host spruce–fir to occupy midelevations, and then whitebark (or some other fiveneedle pine depending on location) to occupy the highest forested habitats. In effect, there is a buffer of non-host forest that serves to spatially separate whitebark from outbreaks in lodgepole. While this is often the case, it is by no means universal. Over large regions of the GYE, there is a seamless intergradation from lodgepole to whitebark pine, typically with a broad elevational zone of a lodgepole–whitebark mixed forest. Lodgepole pine is in no danger of extinction from mountain pine beetle predation since they have a long standing evolutionary relationship that is highly resilient to temperature perturbation. In past climate regimes, the proximity of source beetles in the GYE was moderated by the severe weather of high elevations. Climate warming has resulted in the breakdown of this climate driven spatial isolation. As a consequence, there will be a spatially contiguous reservoir of beetles in lodgepole available to attack whitebark pine as understory (seedlings and saplings) trees assume cone-bearing size. Confounding influence of an introduced pathogen Although WPBR has not been as prevalent in the GYE as farther north in more mesic environments, apparently its prevalence is increasing from 7% in the late 1970s to 27% in 2009 (Interagency Grizzly Bear Study Team 1976–2008). Recent research has confirmed

that trees infected with WPBR are preferentially selected by attacking beetles (Six and Adams 2006, Bockino 2008). Trees too small for the beetle are still vulnerable to WPBR, which will predispose them to attack by beetles when they reach cone-bearing size (Bockino 2008). The synergistic effect of WPBR further reduces the basin of attraction for whitebark pine (Six and Adams 2006). CONCLUSIONS None of the three disturbance ecology attributes we examined bode well for the future of GYE whitebark pine in either the short or long term (see Plate 1). Loss of ecological services in the short term is almost a certainty, and cascading consequences may have already begun to be expressed. Even in areas with substantial recruitment, due to slow growth and maturation of whitebark pine, the availability of seeds for nutcrackers to plant, squirrels to harvest, and bears to eat will not soon be recovered. The same is true for other ecosystem services provided by whitebark pine (Logan and Powell 2009). At best, we are faced with a serious ecological crunch of multi-decade or century magnitude. From a longer temporal perspective, it is conceivable that the fragility of whitebark pine forests to MPB disturbance, combined with other anthropogenic driven ecological stresses like white pine blister rust, could lead to loss of the role as a foundation and keystone species that these climax forests have historically played. Is the situation hopeless? This is a legitimate question in the vein of ecological triage. There are reasons for hope, and in our opinion the most important are these. (1) There are areas within the GYE distribution of whitebark pine that are more resistant to climate change than others. Due to regional climatic influences, some areas we have identified are more resistant than others (Fig. 2D). These could provide refugia for whitebark pine in intermediate time scales (based on current climate predictions). (2) The slow growth rate for whitebark pine leads to both vulnerability and resilience. Resilience results from the fact that the slow growth of seedlings and saplings renders them safe from attack until they reach 6–7 inches (15.2–17.8 cm) dbh (but see discussion regarding WPBR in Domain of attraction: Confounding influence of an introduced pathogen). (3) The Krumholtz growth form is also immune to beetle attack, and under continuing climate warming it may be capable of assuming upright growth in circumstances where cold temperatures are the determinant of growth form. (4) We have described the existence of induced resistance, and this leads to potential active management strategies that might increase resiliency. (5) There are additional active management tactics that could be useful in whitebark pine forests. However, these are derived largely from experience in lodgepole pine, and there are assuredly management options that make sense in lodgepole that may be counterproductive in whitebark. These issues and questions emphasize the crying

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need for research specific to MPB outbreak ecology as expressed in whitebark pine. ACKNOWLEDGMENTS Reviewer comments from Kenneth Raffa, Anna Schemper, Diana Tomback, and an anonymous reviewer significantly improved a previous version of this manuscript; however, any errors in fact or interpretation remain our own. LITERATURE CITED Amman, G. D. 1973. Population changes of the mountain pine beetle in relation to elevation. Environmental Entomology 2: 541–547. Bentz, B. J., and G. Schen-Langenheim. 2007. The mountain pine beetle and the whitebark pine waltz: has the music changed? Pages 43–50 in Whitebark pine: a Pacific coast perspective. R6-NR-FHP-2007-01. USDA Forest Service, Portland, Oregon, USA.

Bleiker, K., and D. L. Six. 2009. Competition and coexistence in a multi-partner mutualism: interactions between two fungal symbionts of the mountain pine beetle in beetleattacked trees. Microbial Ecology 57:191–202. Bockino, N. K. 2008. Interactions of white pine blister rust, host species, and mountain pine beetle in whitebark pine ecosystems in the Greater Yellowstone. Thesis. University of Wyoming, Laramie, Wyoming, USA. Evenden, J. C. 1944. Montana’s thirty year mountain pine beetle infestation. U.S. Department of Agriculture, Bureau of Entomology, Coeur d’Alene Forest Insect Laboratory, Coeur d’Alene, Idaho, USA. Furniss, M. M., and R. Renkin. 2003. Forest entomology in Yellowstone National Park, 1923–1957: a time of discovery and learning to let live. American Entomologist 49:198–209. Gibson, K., K. Skov, S. Kegley, C. Jorgensen, S. Smith, and J. Witcosky. 2008. Mountain pine beetle impacts in highelevation five-needle pines: current trends and challenges. R108-020. USDA Forest Service, Forest Health Protection, Missoula, Montana, USA.

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PLATE 1. In these photographs, the trees with red needles were killed during the previous summer; the gray ‘‘ghost trees’’ remain after the needles drop, beginning the second summer after the tree is killed: (A) near Union Pass, Gros Ventre Range, BridgerTeton National Forest, south-central GYE (Greater Yellowstone Ecosystem, USA); (B) Wisconsin Creek, Tobacco Root Range, Beaverhead National Forest, northwest GYE; (C) two miles southwest of Electric Peak, Gallatin Range, Yellowstone National Park, north-central GYE. Photo credits: W. W. Macfarlane.

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Interagency Grizzly Bear Study Team. 1976–2009. Interagency grizzly bear study team annual report. USGS Northern Rocky Mountain Science Center, Interagency Grizzly Bear Study Team, Bozeman, Montana, USA. Logan, J. A., and B. J. Bentz. 1999. Model analysis of mountain pine beetle seasonality. Environmental Entomology 28:924– 934. Logan, J. A., W. W. Macfarlane, and L. Willcox. 2009. Effective monitoring as a basis for adaptive management: a case history of mountain pine beetle in Greater Yellowstone Ecosystem whitebark pine. iForest 2:19–22. Logan, J. A., and J. A. Powell. 2001. Ghost forests, global warming, and the mountain pine beetle. American Entomologist 47:160–173. Logan, J. A., and J. A. Powell. 2009. Ecological consequences of forest-insect disturbance altered by climate change. Pages 98–109 in F. H. Wagner, editor. Climate warming in western North America. University of Utah Press, Salt Lake City, Utah, USA. Mattson, D. J., B. M. Blanchard, and R. R. Knight. 1992. Yellowstone grizzly bear mortality, human habituation, and whitebark pine seed crops. Journal of Wildlife Management 56:432–442. McCaughey, W. W., and W. C. Schmidt. 1990. Autecology of whitebark pine. Pages 85–96 in W. C. Schmidt and K. J. McDonald, compilers. Proceedings, symposium on whitebark pine ecosystems: ecology and management of a high mountain resource (Bozeman, Montana, 1989). USDA INTGTR-270. USDA Forest Service, Intermountain Research Station, Ogden, Utah, USA. McKinney, S. T., C. E. Fiedler, and D. F. Tomback. 2009. Invasive pathogen threatens bird-pine mutualism: implications for sustaining a high-elevation ecosystem. Ecological Applications 19:597–607. Perkins, D. L., and T. W. Swetnam. 1996. A dendroecological assessment of whitebark pine in the Sawtooth–Salmon river region, Idaho. Canadian Journal of Forestry Research 26: 2123–2133.


Powell, J. A., and J. A. Logan. 2005. Insect seasonality: circle map analysis of temperature-driven life cycles. Theoretical Population Biology 67:161–179. Raffa, K. F., B. H. Aukema, B. J. Bentz, A. L. Carroll, J. A. Hicke, M. G. Turner, and W. H. Romme. 2008. Cross-scale drivers of natural disturbances prone to anthropogenic amplification: the dynamics of bark beetle eruptions. BioScience 58:501–517. Re´gnie`re, J., and B. J. Bentz. 2007. Modeling cold tolerance in the mountain pine beetle, Dendroctonus pondersoae. Journal of Insect Physiology 53:559–572. Safranyik, L. 1978. Effects of climate and weather on mountain pine beetle populations. Pages 77–84 in A. A Berryman, G. D. Amman, and R. W. Stark, editors. Proceedings, symposium: theory and practice of mountain pine beetle management (Moscow, Idaho, April 1978). University of Idaho Forest, Wildlife and Range Experiment Station, Moscow, Idaho, USA. Schwartz, C. C., M. A. Haroldson, G. C. White, R. B. Harris, S. Cherry, K. A. Keating, D. Moody, and C. Servheen. 2005. Temporal, spatial, and environmental influences on the demographics of grizzly bears in the Greater Yellowstone Ecosystem. Wildlife Monographs 161:1–68. Six, D. L., and J. Adams. 2006. White pine blister rust severity and selection of individual whitebark pine by the mountain pine beetle (Coleoptera: Curculionidae, Scolytinae). Journal of Entomological Science 47:345–353. Smith, C. 1995. Fire issues and communication by the media. Pages 65–69 in J. K. Brown, R. W. Mutch, C. W. Spoon, and R. H. Wakimoto, technical coordinators. Proceedings, symposium on fire in wilderness and park management (Missoula, Montana, March 1993). INT-GTR-320. U.S. Forest Service, Intermountain Research Station, Ogden, Utah, USA. Tomback, D. 2008. Director’s message. Nutcracker Notes 15(Autumn/Winter):3. Walker, B., and D. Salt. 2006. Resiliency thinking: sustaining ecosystems and people in a changing world. Island Press, Washington, D.C., USA.