Economics and Politics of Bark Beetles

Chapter 15

Economics and Politics of Bark Beetles Jean-Claude Gre´goire1, Kenneth F. Raffa2, and B. Staffan Lindgren3 1

Biological Control and Spatial Ecology Laboratory, Universite´ Libre de Bruxelles, Bruxelles, Belgium, 2 Department of Entomology, University of Wisconsin-Madison, Madison, WI, USA, 3 Natural Resources and Environmental Studies Institute, University of Northern British Columbia, Prince George, BC, Canada

1. INTRODUCTION—ECOSYSTEMS, HUMANS, AND BARK BEETLES Large bark beetle outbreaks are regarded as major forest disturbances. In the United States, Dale et al. (2001) ranked them first, before hurricanes, tornadoes, and fire, with a 20,400,000 ha average annual impact area and annual average costs (shared with pathogens) above US$2 billion per year. In Europe, over the period 1950–2000, Schelhaas et al. (2003) ranked them third (8% of the total damage), after storms (53%) and fire (16%), with 2.88 million m3 per year between 1958 and 2001 (Seidl et al., 2011). The recent major outbreak of the mountain pine beetle Dendroctonus ponderosae Hopkins in British Columbia and neighboring areas has certainly promoted bark beetles even higher on these scales. The major direct economic consequences of these outbreaks have been widely analyzed, various mitigation methods have been designed and implemented, and diverse political, industrial, and commercial initiatives have been developed to salvage the remains of the devastated forests. At this point, however, the many other, environmental and sociological, consequences of these disturbances are still largely unexplored, although significant progress has been made since Stark and Waters (1987) stressed the importance of understanding the ecological impact of bark beetle damage, regretting the paucity of the information available. A substantial amount of research is now filling this gap. Progar et al. (2009) provide a comprehensive review of the progress in this direction. They outline the multi-scale positive influence of bark beetle activity, from the landscape to stand levels, as well as the various socioeconomic changes brought by bark beetle outbreaks.

2. ECONOMICS 2.1

Damage

Aerial surveys for British Columbia (2001–2010) and western conterminous USA (1997–2010) estimate total Bark Beetles. http://dx.doi.org/10.1016/B978-0-12-417156-5.00015-0 © 2015 Elsevier Inc. All rights reserved.

mortality area (i.e., the area covered by all the dead trees) to be 5.46 million ha (Mha) and 0.47–5.37 Mha, respectively (Meddens et al., 2012). Total bark beetle damage in Europe from 1958 to 2001 was estimated from forest inventory data at about 124 million m3 (Seidl et al., 2011). These striking figures are difficult to compare as they appear in different units (forest areas vs. log volumes), which also illustrates the difficulty to collate and compare damage information.

2.1.1

Silvicultural Consequences

Stand composition and structure are modified by the selective choices of bark beetles. For example, Dymerski et al. (2001) surveyed stands of Engelmann spruce (Picea engelmannii Parry ex Engelm.) in central Utah during a large outbreak of the spruce beetle (Dendroctonus rufipennis Kirby). They found that basal area had decreased by an average 78% in trees larger than 13 cm in diameter at breast height (DBH) in 1996 and by 90% in 1998. Spruce mortality for trees the same size as above averaged 53% in 1996 and 73% in 1998. Stand composition markedly changed, with subalpine fir (Abies lasiocarpa (Hooker) Nuttall) dominating the overstory. In lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Watson) stands in Rocky Mountain National Park, Colorado, 47% of the stems were killed and basal area was reduced by 71% by a D. ponderosae outbreak (Nelson et al., 2014). Average DBH decreased from 17.4 to 11.0 cm, and density decreased from 1393 to 915 stems/ha, while the proportion of non-host species grew from 10.6 to 23.1%. The preferential attack of larger trees suggested above was analyzed and discussed further by Boone et al. (2011), who surveyed lodgepole stands attacked by D. ponderosae in British Columbia. At increasing population densities, the beetles increasingly selected larger trees, despite their stronger defenses. The gaps created by mortality to the largest trees can make stands more vulnerable to wind, hence increasing 585

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the chance of new attacks on windthrows by species such as Ips typographus (L.), D. rufipennis, or D. pseudotsugae Hopkins. Under favorable weather conditions, there may also be increased fire risk during the period when red needles remain in the crown (Kulakowski and Jarvis, 2011). Lynch et al. (2006) analyzed historical records from Yellowstone National Park, Wyoming, for the 25-year period before the 1988 Yellowstone fires and developed a model in which mountain pine beetle activity in the period 1972–1975 increased the likelihood of fire in 1988 by 11% over unaffected areas. From data collected in endemic, epidemic, and post-epidemic Douglas-fir Pseudotsuga menziesii (Mirb.) Franco, lodgepole pine and Engelmann spruce stands, Jenkins et al. (2008) found that changes in fuels over the course of an epidemic either increase or decrease the potential for fire. Globally, bark beetle epidemics result in substantial changes in species composition and altered fuel complexes. Hoffmann et al. (2012) used a fire risk model, the Wildland-Urban Interface Fire Dynamics Simulator, and field data at the tree scale to investigate how tree spatial arrangements and D. ponderosae-caused mortality influenced fire hazard after outbreak. They found a positive link between beetle-caused tree mortality and the intensity of crown fires, while dead needles remained in the crowns. This relationship varied according to stand structure and other factors. For example, linkages between bark beetle outbreaks and fire can also be quite weak (Simard et al., 2011). DeRose and Long (2009), using another simulator, assessed potential wildfire behavior after a massive D. rufipennis outbreak in southern Utah and found a reduced probability of active crown fire for 10 or 20 years, due to a reduction of crown fuel after beetle attack. The host trees species seems thus to influence fire hazards. Page et al. (2014) provides a comprehensive review of the research on effects of D. ponderosae outbreaks on fire. Linkages between fire and bark beetles can potentially work both ways. Surveying ponderosa pine stands attacked by several bark beetle species in the southwestern USA after two wildfires and a prescribed fire, McHugh et al. (2003) found that tree colonization by several Dendroctonus and Ips species was promoted by heavy crown fire damage. Wildfire injury reduces inducible defenses of lodgepole pine against mountain pine beetle (Powell and Raffa, 2011). However, the increased but localized colonization of fire-injured trees is unlikely to cause a transition into outbreaks, unless there is an additional region-wide factor such as severe drought or high temperatures (Hood and Bentz, 2007; Powell et al., 2012).

2.1.2 Environmental Consequences Ecosystem services cover many aspects (Krieger, 2001): watershed services (water quantity and quality; soil

stabilization; air quality; climate regulation and carbon sequestration; biological diversity); recreation (economic impact; wilderness recreation; hunting and fishing; nontimber products); and cultural values (aesthetic and passive use; endangered species; cultural heritage). There have been increased efforts to assign monetary value to ecosystem services, as this can potentially allow for more objective choices in priorities and resource allocation (Costanza et al., 1997; Krieger, 2001). One difficult issue is that the ultimate cost of many decisions that could affect ecosystem services (e.g., the planning of forest operations) is often delayed and, thus, those who benefit in the short term from these decisions are not those who will face their costs. Many ecosystem services can be seriously affected by bark beetle outbreaks (Embrey et al., 2012; see also Chapter 1). Likewise, the costs and benefits of policy decisions are often spatially segregated. For example, high profits can be derived during global trade, while the costs of invasive species are disproportionately high at the local level (Aukema et al., 2011). The water and soil nutrient balance can be affected after an outbreak, before vegetation regrowth (Bosch and Hewlett, 1982; Stednick, 1996; Zimmermann et al., 2000; Brown et al., 2005). Bark beetle damage can result in reduced cover and the reduction of small roots, leading to an increase in ground moisture, an increase in water discharge and recharge and in nutrient uptake. Enhanced insolation leads to increased soil temperature, which in combination with increased moisture leads to faster decomposition and mineralization of the dead biomass. Under conditions of reduced nutrient uptake, there is a higher nitrate concentration in the seepage water, and percolation increases, at least before regrowth occurs. This could increase soil acidity, depending on local conditions, which could lead to increased cation leaching. Increased acidity and aluminum leaching can endanger river ecosystems. A 25 to 40 mm increase in annual water yield per 10% cover change is observed for pine and hardwood forests, respectively (Bosch and Hewlett, 1982), although, according to Stednick (1996), these changes are not noticeable below 20–30% deforestation. Beetle-infested plots have lower C:N mass ratios of pine needlefall than uninfested plots, with higher nitrification rates in the mineral soils from infested plots (Morehouse et al., 2008). The timing and amount of snow melt can be affected by bark beetle activity (Logan et al., 2010; Edburg et al., 2012; Perrot et al., 2014), with earlier snow disappearance under attacked trees. Tree death may reduce protection against avalanches although, according to Kupferschmid Albisetti et al. (2003), spruce snags and dead wood on the ground can still provide some protection for several decades. The present mountain pine beetle outbreak (2000–2014, and continuing) in British Columbia has affected the global

Economics and Politics of Bark Beetles Chapter 15

carbon balance, converting the forest from a small carbon sink to a large source during a long period (2000–2020) (Kurz et al., 2008). However, globally, Canada’s managed forests remain a carbon sink (Stinson et al., 2011). From a conservation perspective, large outbreaks have been shown to increase biodiversity by opening closed conifer stands. For instance, unmanaged outbreak of I. typographus in the German National Park “Bavarian Forest” has favored large numbers of arthropod and plant species with a preference for open habitats (Mu¨ller et al., 2008, 2010; Lehnert et al., 2013).

Starting from the global estimates of Costanza et al. (1997), Krieger (2001) estimated the annual value of ecosystem services provided by temperate/boreal forests to be US$63.6 billion (see also Chapter 1). Price et al. (2010) applied hedonic analysis to property value. They estimated willingness-to-pay to prevent mountain pine beetle damage in Grand County, Colorado. According to their results, property values decline by $648, $43, and $17, respectively, for every tree killed within a 0.1, 0.5, and 1.0 km buffer.

2.1.4 2.1.3 Economic Consequences As suggested above, many consequences of a bark beetle outbreak incur costs: wood losses or downgrading, changes in the ecosystem services, public health consequences, and changes in the landscape aesthetic value. The costs in each of these categories are estimated following different rules. Wood colonized by the fungi associated with treekilling bark beetles often results in large areas of bluestained wood, which reduces the market value of the wood. For example, Chow and Obermajer (2007) found that the volume of bluestain in lodgepole pine wood increased with time since mountain pine beetle attack, with maximum discoloration at about 3 m above ground. Chow and Obermajer (2007) measured the economic implication of this staining by analyzing the percentage of Japanese grade (J-grade) lumber produced, and showed a decrease in J-grade production with increasing time since beetle attack. They recommended early harvest and processing of attacked trees and predicted a reduced supply to the Japanese J-grade market, with an estimated loss of sales of about US$400 million in the following 10 years. Patriquin et al. (2007) used a computable general equilibrium framework to investigate the regional economic impact sensitivity to the current mountain pine beetle infestation in British Columbia and analyzed the short- and long-term changes in timber supply. They concluded that, in the short term, an increased timber supply would favor the regional economies, but that, in the longer-term, the decreasing timber supply would negatively impact regional economies. This raises the concern that severe outbreaks can cause sustainable resource-based economies to behave more like boom-and-bust mining economies. The model can help local decision-makers to develop policies and priority areas for mitigation planning in response to the anticipated fluctuations in timber supply. Fluctuations in employment have strongly impacted local communities in the Alaskan Kenai Peninsula, where timber harvesting developed after the 1989–2004 D. rufipennis outbreak but collapsed when the local wood chip facility closed down in 2004 following the decline in quality of the salvaged wood (Flint et al., 2009).

587

Social Dimensions

The recent outbreaks in North America and Europe triggered a set of studies centered on public health consequences of bark beetle damage, their impact on the standards of living and on employment, the social perception of forest changes and public acceptance of their social, economic, and aesthetic consequences. Embrey et al. (2012) reviewed direct and indirect health impacts in the broader context of ecosystem services and climate changes. They mention increased gastrointestinal disorders brought by higher water turbidity, psychological issues linked to unemployment or loss of property value and, from a more long-term forecasting standpoint, heatrelated mortality and morbidity due to climate change. They also discuss possible prevention strategies and argue that the mountain pine beetle outbreak highlights the need for adopting an ecological, systems-oriented public health approach, able to anticipate all potential health impacts. Flint (2006) analyzed the response of people and communities to a D. rufipennis outbreak on the Kenai Peninsula, by interviews and mail surveys. She observed differences in perception of the impacts of changing forest conditions (fire, falling trees, declining watershed quality and wildlife habitat, economic fluctuations, landscape change, emotional loss). Some communities benefited from increased timber harvesting, others suffered from the loss of the spruce forest, which profoundly affected quality of life, and led to community conflict and economic challenges. She discusses how these different perceptions present both opportunities and difficulties for forest management. In a wider context, Flint et al. (2009) offer a seminal international approach of the human context of forest disturbances by insects. They review four cases of bark beetle forest disturbance: the D. ponderosae outbreaks in British Columbia and north central Colorado, the I. typographus epidemics in the Bavarian Forest National Park, and the D. rufipennis outbreak in the Kenai Peninsula. The diverse communities in these case studies varied in their concerns for different issues (employment, security, changing environment). Findings and lessons learned from these studies are outlined along with their implications for managing forest disturbances by insects in general. Conclusions focus on the need

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Bark Beetles

to assess the broad array of impacts and risks perceived by local residents and the capacity for local action and involvement in managing forest disturbances. From various examples, the study also highlights the variability in cohesiveness of many local communities, and the high need to involve local shareholders in the decision-making processes. Mu¨ller (2011) proposes a comprehensive review of studies concerned with the social dimensions of natural disturbances in forests (wildfires and insects). He also discusses the case of the Bavarian Forest National Park in Germany, which will be examined further in this chapter (see Section 4.1). From surveys among residents and land managers responsible for forest health management in three regions of Alberta suffering a D. ponderosae outbreak, McFarlane et al. (2012) analyze regional variation in the public perceptions of risk, and compare the perception of the residents and the land managers. Residents were not well informed about the mountain pine beetle issue and showed little trust that the provincial government and forest industry would satisfactorily manage the outbreak. Land managers were less concerned about non-timber effects.

2.2

Salvage

Salvaging the wood and restoring the land are also needed when sporadic and local damage occurs due to endemic bark beetle populations. Scale is important, since it influences the market value of the salvaged timber, the technical, administrative and commercial feasibility of silvicultural operations, as well as their overall economic, environmental, and human impacts.

2.2.1 Silvicultural Salvage Sanitary thinning, felling, pest control, and an economic component are commonly performed operations when it comes to restoring forest health (Figure 15.1) (Carroll et al., 2006; Coggins et al., 2011). Removing attacked trees in time prevents damage from new pest generations and, at the same time, preserves lumber value by preventing further wood deterioration by fungal agents or insects. Costeffectiveness analyses can be applied to determine optimal options, e.g., between salvage, quarantine, or biological control (O’Neill and Evans, 1999). Ground surveys, aerial surveys, and satellite image analysis provide foresters with spatially referenced quantitative estimates and, depending on local rules, the local forest services or private companies proceed to salvage logging. For quantitative accuracy and spatial precision, large-scale satellite (Meigs et al., 2011) or aerial monitoring can be complemented by targeted helicopter surveys, followed by ground surveys (Coggins et al., 2011). Ground surveys can be tailored to fit local constraints. For example, in southwestern France, Samalens

FIGURE 15.1 Logging operation near Prince George, British Columbia. Each bunch of logs corresponds to one or several truckloads. Photo: J.-C. Gre´goire.

et al. (2007) designed an adaptive technique of road sampling for assessing the damage of Ips sexdentatus (Boerner) in plantations of Pinus maritima Mill. Sometimes, indirect ways can be used (Meurisse et al., 2008). The use of thinning to mitigate bark beetle outbreaks has always generated contention and controversy, and components of these arguments remain. For example, Six et al. (2014) argue that while thinning may decrease the likelihood of outbreaks erupting, and so may have some benefit as a proactive tool, its ability to reduce outbreaks already under way is not supported by evidence. Fettig et al. (2014) emphasize that it is important to distinguish these functions, as well as additional management intentions of thinning operations, and that understating such distinctions can have negative policy implications through lost opportunities. Likewise, Black (2005) argued that the evidence for deleterious effects on non-target invertebrates was stronger than that for effective pest management, a view disputed by Fettig et al. (2007). Under outbreak conditions, these operations are complicated by decreasing prices for the wood, competition for

Economics and Politics of Bark Beetles Chapter 15

loggers, machinery and logging trucks, and the availability of an extensive road network. In many cases, it then becomes difficult or impossible to remove the killed trees soon enough to prevent damage to the wood. Strategic choices must be made (e.g., to increase harvest) when infestation levels exceed a certain threshold (Bogle and van Kooten, 2012). In the southern Rocky Mountains, it is foreseen that terrain, economic, and administrative limitations will limit salvage logging to a small fraction (<15%) of the forests killed by D. ponderosae (Collins et al., 2011). Several critical issues arise from salvage logging. One of them is the destination and use of the salvage timber. Flint et al. (2009) analyzed this issue in Colorado in the context of the D. ponderosae outbreak. Communities highly dependent on tourism and recreation were less supportive to large-scale forest industry, which, on the other hand, received more support in areas with an existing tradition in resource extraction. There was a wide cross-community support for small-scale niche markets (e.g., posts and poles and furniture) and biofuel energy production. From the biodiversity standpoint, Foster and Orwig (2006) concluded from a study in New England that leaving the forest alone brought more ecological benefits than salvage logging. This debate has also been widely explored around I. typographus outbreaks in Germany (see Section 4.1). Carbon budgets can also be influenced by salvage logging. A study of harvested vs. unharvested stands in British Columbia after the mountain pine beetle outbreak showed carbon release in the harvested stands even 10 years after harvesting, while the unharvested stands were still carbon sinks (Brown et al., 2010). Tree regeneration was compared in the southern Rocky Mountains between paired harvested and untreated lodgepole pine stands that had suffered more than 70% mortality due to D. ponderosae (Collins et al., 2011). In harvested stands, the density of new seedlings was four times higher than in the non-harvested stands. Growth simulations suggested that lodgepole pine will remain the dominant species in harvested stands, while A. lasiocarpa will become the most abundant species in untreated areas.

2.2.2 Industrial Salvage Bark beetle outbreaks generate changes in different directions in the market value of timber and wood derived products. At first, the sudden increase of raw materials reduces the market value of wood. Later on, yearly harvests can be regulated to compensate for the depletion caused by the insects, affecting global log and lumber prices. Abbott et al. (2009) reported that the 2006 harvest in British Columbia was 8.7 million m3 above the pre-outbreak annual allowable cut, and that, after 2009, the allowable

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annual cut would be reduced by 12 million m3. Other products can then be developed, such as bioenergy (Pan et al., 2007, 2008; Stennes et al., 2010; Luo et al., 2010; Zhu et al., 2011). More information can be found in Section 4.4.

3. 3.1

POLITICS Management

A global approach is needed for large area-wide outbreaks. Abbott et al. (2008, 2009) consider the economics of the mountain pine beetle outbreak in British Columbia in an international context, where province-wide forest management policies and the international market for timber and wood products must be simultaneously taken into account. Public policies also bear on forest management and vary worldwide, in terms of regulatory constraints and financial incentives, with variable weight on either public support or private initiative. Brunette and Couture (2008) analyzed how some European governments compensate forest owners for windstorm damage. They concluded that this policy is likely to interfere with the propensity of private forest owners to purchase a personal insurance policy for the coverage of natural disturbances and develop a proactive attitude towards prevention. Sims et al. (2010) developed a bioeconomic model of tree harvesting after mountain pine beetle damage, to measure the consequences of alternative public management strategies. They suggest that the commonly practiced procedures increase the severity of mountain pine beetle cycles, while more centrally coordinated management could eliminate mountain pine beetle cycles and lessen their impacts with only small reductions in the long-run stock of wood. Watson et al. (2013) were interested in cost sharing for pre-commercial thinning (PCT) in pine plantations in Virginia, in view of reducing southern pine beetle (Dendroctonus frontalis Zimmermann) risks. PCT has a cost and delayed impact; therefore, it is not always seen positively by landowners. The Virginia Pine Bark Beetle Prevention Program attempts to reconcile differing public attitudes by partly reimbursing PCT costs. A survey sent to landowners indicated a significant, positive effect of cost sharing on willingness to participate, with a 50% upper limit of reimbursement beyond which participation is unlikely to increase substantially. Management policy also includes the choice of tree species for replanting. In a meta-analysis, Bertheau et al. (2010) showed that, in some limited instances, some pest species have a higher fitness on exotic trees. It has been frequently observed that native trees are more sensitive to exotic pests. For example, Dendroctonus valens LeConte is a tree killer in China, while it is much less aggressive

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in North America (Sun et al., 2013; Chapter 8). Forest biodiversity has also been shown to increase stand resilience (Jactel and Brokerhoff, 2007), and replantation policies could be designed along these lines.

3.2

Anticipating Trouble

3.2.1 Predictive Models Various types of models are used for risk prediction, phenology planning, anticipation of spatio-temporal population changes or, more prospectively, for anticipating the effects of climate change (Hansen et al., 2001a; Williams and Liebhold, 2002; Gan, 2004; J€ onsson et al., 2007; Seidl et al., 2008; Waring et al., 2009; Bentz et al., 2010; Evangelista et al., 2011; Temperli et al., 2013). A synoptic presentation of such models developed to date for I. typographus is given in Table 15.1.

3.2.2 Exotic Species Exotic bark beetles are frequently intercepted with imported goods and materials. Haack (2001) reported 6825 records of bark and ambrosia beetles from countries outside of North America that had been intercepted during the 1985–2000 period at US ports of entry. Similar information for New Zealand is provided by Brockerhoff et al. (2006). Most of the insects come in wood packaging material containing various goods (tiles, marble, machinery, steel, ironware, granite, slate, etc.) (Haack, 2001). An International Standard for Phytosanitary Measures (ISPM 15) has since been established (FAO, 2009), which requires that the wood is debarked, and either heat treated (at a minimum temperature of 56
C for a minimum duration of 30 minutes) or fumigated with methyl bromide, although this latter treatment is being phased out. However, ISPM 15 does not totally guarantee bark beetle-free importations. Analyzing importation data for goods entering into the US, Haack et al. (2014) found only a small reduction in contaminated wood packaging material following implementation of ISPM15, from about 0.2% (for the 2 years pre-ISPM) to about 0.1% (for the 4 years following ISPM15). There are numerous examples of introductions of exotic bark beetles, e.g., Dendroctonus micans Kug. in Britain (Bevan and King, 1983), Tomicus piniperda L. in North America (Haack and Lawrence, 1994), and D. valens in China (Sun et al., 2013). A recent occurrence is the discovery of the thousand cankers disease pathogen Geosmithia morbida Kolarˇik (Ascomycota: Hypocreales) and its vector Pityophthorus juglandis Blackman on an infected walnut tree in Italy in 2013 (Montecchio and Faccoli, 2014). International regulations such as ISPM15, national quarantine regulations implemented by each national plant protection organization, and inspections at the national borders

are methods developed to mitigate this threat, but they are obviously not 100% effective.

4. A DIVERSITY OF PATTERNS— ILLUSTRATIVE CASE STUDIES Five specific cases are illustrated by a more thorough presentation: the eight-toothed spruce bark beetle in Eurasia; secondary ambrosia beetles attacking living beech in Europe; the spruce beetle in North America; the mountain pine beetle crisis in British Columbia; and the Eastern pine engraver across the continent.

4.1 Fallen and Standing Alike—The Eighttoothed Spruce Bark Beetle in Eurasia Ips typographus is a pest of spruce (Picea spp.) throughout Eurasia. At endemic levels, it attacks windthrows or snowbreaks, but when populations grow, it can kill standing trees (Christiansen and Bakke, 1988). Wermelinger (2004) provides a comprehensive review of the biology and management of this species. Depending on competition and natural enemies, each attacked tree produces 25,000 to 70,000 individuals (Fahse and Heurich, 2011 and references therein; Gonzalez et al., 1996). Gre´goire et al. (1997) counted on average 4800 to 6400 beetles of both genders attacking new host trees in about 1.5 m3 in volume. Comparing these two sets of figures suggests that, when a substantial proportion of the emerging insects can find a susceptible host (e.g., after a storm), catastrophic outbreaks can easily develop, especially in multivoltine populations. Ips typographus is the most damaging of the bark- and wood-boring insects attacking living trees in Europe (Gre´goire and Evans, 2004). According to Carpenter (1940), 15 outbreak episodes occurred between 1769 and 1931. Bark beetles (mainly I. typographus) have been responsible for losses of about 2.9 million m3 of spruce timber per year in Europe during the period 1950–2000 (Schelhaas et al., 2003). Recent detailed data for Switzerland, France, Austria, and Sweden are provided in Table 15.2. Dale et al. (2001) listed seven major disturbances affecting forests, including insects and hurricanes. In the case of I. typographus, both disturbances are combined, as outbreaks usually occur after storms (Table 15.1), in particular when the windthrown host trees are not removed fast enough (Schroeder and Lindel€ ow, 2002; Schelhaas et al., 2003). Insect success is increased by dry and hot springs and summers (another combination of disturbances), and the value of the attacked timber decreases as infestation time increases. The wood is first stained by the pathogenic fungi (e.g., Ophiostoma sp.) associated with the beetles (Figure 15.2). This does not affect its structural properties (Chow and Obermajer, 2007) but can

TABLE 15.1 Risk Models Developed for the Management of Ips typographus in Europe Data

Method

Main Results

Faccoli (2009)

Risk model Investigate the possible weather effect on the biology of and damage caused by I. typographus in the southeastern Alps.

Temperature records (1962– 2007), precipitation data (1922– 2007), damage caused by I. typographus (1993–2007). Data from pheromone-baited traps (1996–2005) in the southeastern Alps.

Statistical model - multiple regressions.

 Damage caused by I. typographus was inversely correlated with March-July precipitation from the previous year but not correlated with temperature.  Spring drought increased damage caused by I. typographus in the following year, whereas warmer spring affected insect phenology.

Fahse and Heurich (2011)

Risk model

Data (1994 to 2009) from the recent outbreak in the Bavarian Forest National Park (Germany).

Spatially explicit agent-based bottom-up simulation model taking into account individual trees and beetles (SAMBIA).

 Distinct threshold above a certain level of impact from natural enemies or silvicultural management.  Also validated by the model: anisotropic growth of infestation spots; abrupt collapse of attacks even in the presence of potential host trees.

Jakusˇ et al. (2011)

Risk model Define the characteristics of individual Norway spruces that survived a massive bark beetle outbreak.

Measurements made in the Sˇumava National Park (Czech Republic).

Statistical model, based on parameters related to crown geometry, stand conditions and distances between trees.

 Trees with a longer crown length tended to survive.  Attacked trees usually located in the south aspects of areas with larger basal areas.  Probability of additional attack inversely proportional to distance to a previously attacked tree.

J€ onsson et al. (2012)

Risk model Analyze the influence of multiple environmental factors on the risk for I. typographus outbreaks.

Gridded daily climate data covering Sweden (spatial resolution: 0.5
). Data on storm damage and I. typographus outbreak in 1960–2009.

Ecosystem modeling approach. “Model calculations of I. typographus phenology and population dynamics as a function of weather and brood tree availability were developed and implemented in the LPJ-GUESS ecosystem modeling framework.” Sensitivity analysis.

 Good fit between the model simulations and the observed pattern in outbreak frequency.  Higher risk for attacks on living trees under a warmer climate allowing multivoltinism.  Timely salvage cutting and removing of infested trees leads to a major reduction in the risk of attacks on living trees.

Ka¨rvemo et al. (2014)

Risk model Locate areas of high risk for tree mortality across forest landscapes.

Calibration and validation data each from a different set of 130,000 ha of managed lowland forest in southern Sweden in 2007–2009, at a 100  100 m resolution.

Statistical model based on boosted regression trees.

 Host tree volume ha1 (up to 200 m3 ha1) was the most important predictor of beetle attack.  Birch volume of (up to 25 m3 ha1) also positively correlated with infestation risk.  Tree height (above 10–15 m) associated with increased infestation risk.  The attacked trees are distributed in many small spots spread out over the landscape.

 Analyze the spatial and temporal aspects of bark beetle outbreaks at the stand scale.  Assess the impact of both antagonists and management.  Predict outbreak probabilities under different conditions.

Continued

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Type of Model/Objectives

Economics and Politics of Bark Beetles Chapter 15

References

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TABLE 15.1 Risk Models Developed for the Management of Ips typographus in Europe—cont’d Type of Model/Objectives

Data

Method

Main Results

Lausch et al. (2011)

Risk model Identify key habitat variables (topography; climate; soil type; forest stage; biological/structural characteristics of the patch) influencing attack risk.

Annual color-infrared aerial photographs (1:10,000–1:15,000) of deadwood areas (100% mortality due to I. typographus) taken from 1990 to 2007 in the Bavarian Forest National Park (Germany).

Ecological Niche Factor Analysis (ENFA) models calculated yearly from a spatially explicit database.

 No single causal factor was identified over the entire model period.  The distance from the previous year’s infestation and the area and perimeter of the previous year’s infestation patch influenced the probability of a new attack, but not across all years.

Netherer and Nopp-Mayr (2005)

Risk model Identify mechanisms of disturbance agents and establish spatial distribution of predisposed stands.

Forest inventory data from the Slovak and Polish High Tatras National Parks, combined to a digital elevation model.

A spatially explicit predisposition assessment system was developed, scoring abiotic and biotic factors based on the literature and expert advice. The resulting predisposition scores (11 sites and nine stand criteria) were compared to the distribution patterns of damaged and undamaged forest stands.

 At the site level, the distribution of sound and attacked forest units was significantly different between low-medium and high scores of “Radiation” and between the categories of “Slope Position.”  At the stand level, higher values for the criteria “Proportion of Spruce,” “Age Class,” “Predisposition to Storm Damage,” and “Stand Density” significantly characterized attacked forest units.

Pasztor et al. (2014)

Risk model Develop tools to assess the risks of damage from bark beetle disturbances at the operational scale of forest stands.

Ten-year forest management plans and related harvest records of four management units of the Austrian Federal Forests (40,000 ha) within the 1992–2010 period; gridded climate data set provided by the Austrian Central Institution for Meteorology and Geodynamics.

Statistical binomial generalized linear mixed models were used to assess the effects of site, stand, and climate conditions on the probability of bark beetle disturbance events at forest stand level, and linear mixed models to assess the intensity of these events.

 Increases in some of the predictor variables increased probability of damage substantially, mainly previous bark beetle damage during the four previous years and current timber stock.  Potential bark beetle generations estimated from a beetle phenology model were also a useful predictor.  The model of disturbance probability correctly classified 90% of all cases in the dataset (specificity 95%, sensitivity 29%).  The model for damage intensity explained only low shares of the variation in the recorded damage data.

Schmidt et al. (2010)

Risk model Storm damage risk of for individual trees.

Individual tree damage data from the storm “Lothar” (1999) in Baden-Wu¨rttemberg (Germany).

Statistical model inferring probability of damage, and separating the effects of treedependent variables, topography, site conditions, and flow field related effects.

 Good validation of predicted geographical location of risk hotspots using forest service data.  Tree height (but not height to DBH ratio) influences damage.  Picea abies has the highest damage potential.  Higher risks for west- to south-exposed locations and waterlogged soils show an increased risk.

Bark Beetles

References

Risk model Assess the impact of drivers influencing bark beetle infestations at the forest district level, in particular salvage logging and sanitation felling.

Annual survey dataset covering nine years and 487 Swiss forest districts (82% of the forested area).

Statistical Poisson log-normal models.

 Bark beetle damage proportional to storm damage, heat sum, volume of Norway spruce stock, and the number of infestation spots in the previous year.  Damage inversely proportional to sanitation felling relative to the total volume of infested spruce, and to proportions of salvaged windthrows.

Zolubas et al. (2009)

Risk model

Fixed-radius plots around attacked trees or controls in 80–100-yearold Picea abies pure stands. Ninety-two paired plots in 2000– 2002. Characteristics under endemic bark beetle densities.

Statistical model—classification and regression trees.

 Most significant variable: spruce basal area, positively correlated with risk.  Lack of sensitivity for decision-making (70% of the non-attacked (control) plots and 88% of the attacked plots are in the “high risk” category).

Marini et al. (2012)

Population dynamics model Characterize the combined effects of climatic factors and densitydependent feedbacks on damage; test whether climate modify the species’ altitudinal outbreak range.

Sixteen-year time-series of P. abies timber loss due to I. typographus attacks and abiotic events in the Friuli-Venezia Giulia region (Italy). Annual time series (1994–2009) from daily climatic data from eight meteorological stations distributed over the region.

Discrete population dynamics model and information theoretic approach.

 Dry summers combined with warm temperatures appeared as the main abiotic triggers of severe outbreaks.  Endogenous negative feedback with a 2-year lag suggesting a potential important role of natural enemies.  Forest damage would be on the average sevenfold higher in warmer sites than in spruce’s historical climatic range.  Dry summers (not temperature) influence upward altitudinal shifts of the outbreaks.

Marini et al. (2013)

Population dynamics model Quantify and compare the relative importance of predation, negative density feedback, and abiotic factors as drivers of I. typographus population dynamics.

Pheromone-baited traps from 1995 to 2011 in two 60,000 ha areas in central Sweden, and two areas in southern Sweden. Temperature and rainfall data. Annual amount of timber loss due to snow and wind.

Discrete population dynamics model; multi-model inference approach.

 The main outbreak trigger was the availability of breeding substrates (windthrows).  The main endogenous regulating factor was a strong intraspecific competition for host trees.  Temperature-related metrics did not significantly influence population dynamics, even though they are known to influence voltinism.  Predator (Thanasimus formicarius) density did not exert any important regulating impact.

Økland and Berryman (2004)

Population dynamics model Identify the role played by resource dynamics in regional population changes.

Time series of pheromone trap catches from 1979 to 2000 in approximately 100 localities throughout southeast Norway.

Statistical model at two spatial scales (whole area and 12 subregions); additional analyses of time-series before and after a large windfelling in 1987.

 The endogenous dynamics were dominated by lag 1 density dependence.  Windfelling appears to be an important predictor of the dynamics; uncertainty due to only one large windfall event in the time series.  Weak influence of drought stress; uncertainty linked to the absence of severe droughts within the time series.

Economics and Politics of Bark Beetles Chapter 15

Stadelmann et al. (2013b)

593

Continued

594

TABLE 15.1 Risk Models Developed for the Management of Ips typographus in Europe—cont’d Type of Model/Objectives

Data

Method

Main Results

Baier et al. (2007)

Phenology model Spatio-temporal simulation of I. typographus’ seasonal development in Kalkalpen National Park, Austria.

Digital elevation model for interpolating temperature and solar radiation, as well as air and bark temperature measurements.

Phenology model (PHENIPS), using a flight initiation lower threshold of 16.5
C and thermal accumulation of 140 degree-days (dd) from April 1st onward (upper and lower thresholds: 38.9 and 8.3
C, respectively). Thermal sum for total development: 557 dd. Reemergence of parental beetles when 49.7% of this sum is reached. Discontinuance of reproductive activity at a day length <14.5 h.

Spatially explicit estimate of local maximum number of generations, allowing to predict the potential impact of bark beetle outbreaks.

J€ onsson et al. (2009)

Phenology model Describe the temperature thresholds for swarming and temperature requirements for development from egg to adult for three future climate change scenarios during the period 1961– 2100.

Daily climatic data (1961–2100) from three climate change scenarios obtained from the Rossby Centre Regional Climate Model RCA3 with different adjustments.

Phenology model. The model of J€ onsson et al. (2007) was used, with some adjustments.

 I. typographus able to initiate a second generation in south Sweden during 50% of the years around the mid-century.  By the end of the century, a second generation will be initiated in south Sweden in 63–81% of the years; and less frequently in the rest of the country.  Later, 1–2 generations per year are predicted, and the northern distribution limit for the second generation will vary.

J€ onsson et al. (2011)

Phenology model Extends the existing model of J€ onsson et al. (2007), based on temperature only by including reproductive diapause initiated by photoperiodic and thermal cues; use this extended model to assess the impact of global warming on voltinism in I. typographus.

Three different climate datasets (1950–2010) including climate change scenarios. Monitoring data from trap catches over various periods between 1979 and 2007, according to country (Sweden, Norway, Denmark).

Phenology model based on several steps: (1) comparison of the output of a phenology model and monitoring data; (2) development and parameterization of a diapause model; (3) analysis of model sensitivity; (4) inclusion of climatic scenarios in the model.

 Higher temperatures can result in increased frequency and length of late summer swarming (producing a second generation in southern Scandinavia and a third generation in lowland parts of central Europe).  Reproductive diapause will not prevent the occurrence of an additional generation per year.  However, day length could restrict late summer swarming.

Gilbert et al. (2005)

Spatial model Study large-scale patterns in bark beetle populations that would benefit from the abundant breeding material provided by the 1999 storm in France.

Large-scale survey in the spring and in the autumn of 2000, after the December 1999 storm, in 898 locations distributed throughout wind-damaged areas in France. Local abundance of four conifer bark beetle species scored on a 0 to 5 scale.

Geostatistical estimators to explore the extent and intensity of spatial autocorrelation. Statistical analysis to correlate results with site, stand, and neighborhood landscape metrics of the forest cover.

 Large-scale spatial dependence and regional variations in abundance.  Significant relationships with the number of coniferous patches.

Bark Beetles

References

Kautz et al. (2011)

Spatial model Quantify the spatio-temporal dispersion of I. typographus:  Parameterize the size and shape of infestation patches.  Model an infestation gradient.  Assess the risk of subsequent infestations at the landscape scale.

Analysis of attacked patches (5 trees), based on a 22-year time series of annual color-infrared images (1:10,000 to 1:15,000) of a 130 km3 area in the Bavarian Forest National Park (Germany).

GIS-based spatial correlations between successive patches calculated by a distance ring approach based on nearest distance relations. Overlaying this distribution with the distribution of potential hosts.

 The infestation spread was strongly distance dependent, following an inverse power law.  On average, 65% of new infestations occurred within a 100 m radius of the previous year’s infestations, and 95% within 500 m.  During outbreak periods within the study’s time series, a higher percentage of infestations within short distance (<100 m) were observed.  Larger patches tended to have more complex shapes.

Color-infrared aerial photographs (1:10,000–1:15,000) of deadwood areas (100% mortality due to I. typographus) taken twice a year (June–July and September– October) from 1988 to 2010 in the Bavarian Forest National Park (Germany).

Spatially explicit variables seen as meaningful for structure and pattern analysis were calculated using the structural analysis program FRAGSTATS. Comparison with, and incorporation to, an agent-based simulation model (SAMBIA) (Fahse and Heurich, 2011).

 Non-directional movements of the centroid of the deadwood patches from 1988 to 2001.  Northeast-southwest movement during the 2001–2007 period.  The mean Euclidean nearest neighbor distance of dead wood patches over the whole period was 116 m (143), the minimum was 22 m.

Wichmann and Ravn (2001)

Spatial model Analysis of dispersion patterns of infestation spots after an outbreak.

Field collected data from the forest of Rold Skov (7280 ha; Denmark) in 1982–1983: ground surveys of windthrown areas and infestation patches, salvage harvests and pheromone trap catches.

GIS and statistical analyses.

 Attack densities were not spatially correlated with trap catches.  Attack densities were correlated with the timing of salvage harvests (the later the harvest, the higher the attacks).  Nearly 90% of the new attacks occur within 100 m from an old attack, nearly 80% within 50 m, and 50% of the new attacks occur within 20 m from an old attack.

J€ onsson et al. (2007)

Climate change model Evaluate the effect of regional (southern Sweden) climate change scenarios for the period 2070– 2099.

Temperatures data (1961–1990). Bark beetle activity monitored in 1980, 1981, 1984, and 1985 used for validating the model.

Phenology model based on the relationship between thermal conditions and phenology models of I. typographus presented in the literature.

 Step-wise effect of temperature increase on the population dynamics.  Earlier spring swarming and faster development increase the probability of a second swarming during summer.  Because immature stages die during the winter, the autumn temperature will have a decisive impact on the population size of the following spring.

Seidl et al. (2008)

Climate change model Effects of bark beetle disturbance on timber production and carbon sequestration over 100 years.

Norway spruce management unit in Austria.

Simulation under two scenarios of climatic change, including a submodule of bark beetle-induced tree mortality, under four management strategies (no managements; three active management strategies).

 Strong increase in bark beetle damage under climate change scenarios.  Reduced C storage in the actively managed strategies.  Under some scenarios: increased C sequestration in unmanaged control (stand density effect).

 Describe the long-term spatiotemporal infestation patterns of I. typographus in the Bavarian Forest National Park (Germany), at the landscape scale.  Analyze the spatio-temporal movements of infestation patches.

Continued

595

Spatial model

Economics and Politics of Bark Beetles Chapter 15

Lausch et al. (2013)

596 Bark Beetles

TABLE 15.1 Risk Models Developed for the Management of Ips typographus in Europe—cont’d References

Type of Model/Objectives

Data

Method

Main Results

Temperli et al. (2013)

Climate change model Identify and assess the mechanisms and feedbacks driving short-term and long-term interactions between beetle disturbance, climate change, and windthrow. Predict how they may change in the future.

Model parameterization using measurements of infested area from the recent outbreak in the Bavarian Forest, Germany (Kautz et al., 2011) and monthly climate data from the Black Forest (1950– 2000).

Spatially explicit model incorporating beetle phenology and forest susceptibility, and integrated in a climate-sensitive fine-grain landscape model (LandClim) Four spatiotemporal scales: shortterm, patch scale; short-term, landscape scale; long-term, patch scale; long-term, landscape-scale Baseline climate compared to a weak and a strong climate change scenario.

 Short-term, patch scale: spruce age, spruce share, drought index, and windthrown spruce biomass positively correlated alone and in combinations with tree susceptibility; increased infestation probabilities occurred in decades with large windthrow events.  Short-term, landscape scale: windthrow had a comparatively weak influence on bark beetle damage because it affected only a small fraction of the landscape, whereas changes in temperature and drought affected trees throughout the landscape.  Under climate change scenarios, beetle activity combined with warmer and dryer conditions at the drier-warmer parts of the new range, generating a negative feedback for the beetles by suppressing the host trees.

Economics and Politics of Bark Beetles Chapter 15

597

TABLE 15.2 Storm Damage and Subsequent Damage caused by Ips typographus in Germany, Switzerland, France, Sweden, and Austria Country (storm) Germany

Switzerland (Vivian)

Switzerland (Lothar)

France (Lothar)

Storm Damage (m3)

I. typographus Damage (m3)

Date

Damage (spruce)

Date

Damage

References

1972

9,200,000 m3

1972

>8000

Abgrall (2000)

1973–1975

>567,450

1976–1978

>134,920

1990

60,000

1991

140,000

1992

500,000

1993

480,000

1995

300,000

1995

135,000

1996

289,000

1997

90,000

1998

87,000

1999

86,000

Total

2,167,000

2000

162,000 NB—warm spring and summer

2001

1,300,000

2002

1 100,000

2003

2,067,000 NB—extremely hot summer

2004

1,350,000

2005

1,015,000

2006

727,000

2007

285,000

2008

85,000

2009

100,000

Total

8,191,000

1999

24,500

2000

–

2001

514,000

2002

295,000

2003

308,700 NB—extremely hot summer

2004

378,000

2005

453,000

Total

1,948,700

1990

1999

1999

5,000,000 m

8,000,000 m (spruce)

3

3

3

87,600,000 m (all conifers, North-Eastern France)

Abgrall (2000)

Meier et al. (2013) WSL—Forest Protection Overviews, 2014

Nageleisen (2006, 2007) (partial reports, for North-Eastern France)

Continued

TABLE 15.2 Storm Damage and Subsequent Damage caused by Ips typographus in Germany, Switzerland, France, Sweden, and Austria—cont’d Country (storm) Sweden (Gudrun)

Austria

I. typographus Damage (m3)

Storm Damage (m3) Date

Date

Damage

References

2005

3

75,000,000 m

2006

1,500,000

Lindel€ ow and Schroeder (2008)

2007

12,000,000 m3

2007

>500,000

2002

4,000,000 m3 (all tree species)

2002

545,762

2003

1,485,421

2004

1,945,001

2005

2,148,970

2006

1 953,765

2007

1,738,468

2008

1,563,216

2009

2,470,772

2010

2,350,623

2011

1,375,634

2012

702,126

Total

18,279,758

2007– 2008

Damage (spruce)

Ca. 18,700,000 m3 (all tree species)

Steyrer and Krehan (2009); Krehan et al. (2012); Bundesforschungszentrum fu¨r Wald. (2014)

FIGURE 15.2 Blue staining (Ophiostoma sp.) and symptoms of lignivorous fungi, Stereum sanguinolentum (Alb. and Schwein.) Fr. (brown staining) on a standing spruce mass attacked and killed six months previously. Right figure: close up of the blue and brown staining. Photo courtesy Emmanuel Defay.

Economics and Politics of Bark Beetles Chapter 15

reduce its value by 50%. Later on, lignivorous fungi (e.g., Stereum sanguinolentum (Alb. and Schwein.) Fr.) may colonize the wood, which then loses most of its remaining value. The damage caused by I. typographus is not restricted to timber losses and changes in silvicultural planning. In mountainous areas, losing the trees represents a reduced protection against avalanches (Bebi et al., 2012). However, leaving the snags on the slope can still provide effective protection for about 30 years (Kupferschmid Albisetti et al., 2003). The environmental and social impacts of I. typographus outbreaks have been only partially investigated. The Bavarian Forest National Park in Germany is an extremely rich source of information regarding the multiple features of a large and long-lasting I. typographus outbreak, because of its unique beetle management rules. The National Park was established in 1970 and now covers more than 240 km2. Its large forests have been allowed to develop free of human interference. In direct continuity, on the other side of the border with the Czech Republic, the 690 km2-wide Sˇumava National Park is also a protected area. These protected zones are only a part of the Bavarian Forest Nature Park (3070 km2) and the Sˇumava Protected Landscape Area (1000 km2), respectively. The entire area is known as the “Greater Bohemian Forest Ecosystem” (Heurich et al., 2011). Large outbreaks of I. typographus occurred in the park in the 1980s after several windthrow events. A decision was made at that time to exert no control on the beetles in the natural zone of the national park. This decision is still under effect and as a result the outbreak is still ongoing. Consequently, the spruce forest has been killed in over 6000 ha (Lausch et al., 2011). This exceptional situation of an undisturbed beetle population over a vast territory has allowed in-depth investigations regarding various negative or positive impacts of the bark beetles, as well as extensive modeling. Some aspects of the environmental impacts of I. typographus have been measured in the Bavarian Forest National Park. Measurements on a 110 ha water catchment characterized by 81% dead trees at the end of a 1989–1999 observation period showed a steep increase of the runoff/ precipitation ratio (0.84 in 1997–1999 vs. 0.64 in 1989– 1996), correlated with deforestation. Nitrate concentration in the soil solution peaked (up to 60 mg/l) at 50 and 100 cm depth during the first 4 years of beetle activity, then decreased with the regrowth of the vegetation. Nitrate leaching was important, with peak values temporarily exceeding 50 mg/l in seepage water and 25 mg/l in springs and streams (Zimmermann et al., 2000). Similar observations were made by Huber (2005), who also found spatial heterogeneity in nitrate leaching, which he attributed to different patterns of vegetation regrowth. Ips typographus can also have positive effects. In the Bavarian Forest National Park, the recolonization dynamics

599

of the 5800 ha of naturally occurring Norway spruce stands killed by I. typographus from 1988 to 2010 (Lausch et al., 2013) was studied by Lehnert et al. (2013) and Mu¨ller et al. (2008, 2010), who concluded that I. typographus is a “keystone species” for the maintenance or improvement of forest biodiversity, because its activities open the stands, and the deadwood it creates favors endangered saproxylic beetles. In Switzerland, salvage logging resulted in considerable amounts of deadwood, providing a key resource for biodiversity (Priewasser et al., 2013). In Sweden, Schroeder (2007) followed six reserves hit by a storm in 1995 and found that 81% of the snags remaining in 2006 were from bark beetle-killed trees (19% were felled by the storm) and argued that preserving bark beetle-killed trees would be a cost-effective means to increase the amounts of coarse woody debris in the forest, hence favoring endangered saproxylic species. Public perception of I. typographus outbreaks has also been analyzed in the Bavarian Forest National Park. As central stakeholders in the national park, tourists are facing scenes of utter devastation, which do not correspond to their expectations. Mu¨ller and Job (2009) used structural equation modeling to compare three models explaining their “bark beetle attitude.” They found that, globally, tourists have a neutral attitude towards bark beetles but that tourists with a higher familiarity with the park have a more positive attitude towards the park’s policy. Mu¨ller (2011) analyzed political conflicts going on for 20 years within and around the park regarding bark beetle management. He describes two diverging attitudes, one of them hostile to the present policy, seen as imposed by external forces, the other more favorable. “Sauber Forstwirtschaft” (clean forestry) has long been a practical or legal rule in European countries, prescribing that felled conifers must be peeled, and that bark beetleattacked trees must be immediately removed from the stands. When comparing tree mortality during the years following a storm in Sweden, fewer trees were killed by the beetles during the first year in unmanaged stands (windthrows not removed) than in managed stands, probably because the windthrows left in place captured most of the insects the year following the storm (Schroeder and Lindel€ow, 2002). This trend reversed in subsequent years, however, and in the 4-year period after the storm, twice as many trees were killed per ha in the unmanaged stand as compared to the managed stands. In a recent study covering 9 years and 487 forest districts in Switzerland, Stadelmann et al. (2013a) provide quantitative arguments in favor of salvage-logging, stressing the priority of salvage logging after a storm. J€onsson et al. (2012) reached similar conclusions from a modeling approach in Sweden. As discussed above, the situation of national parks is particular, because their priorities focus on biodiversity. In the Sˇumava National Park (Czech Republic), salvage logging had a

600

Bark Beetles

FIGURE 15.3 Stocks of windthrows stored under sprinkling water in the Vosges (France) after the Lothar storm (December 1999). The pictures were taken in June 2002. Photos: J.-C. Gre´goire.

detrimental effect on forest recovery, compared to leaving the dead trees on site (Jona´sˇova´ and Prach, 2008). Salvage logging often requires careful planning, in particular when very large amounts of timber become suddenly available, with markets plummeting and with logging personnel and equipment in very high demand. Often, the vast amounts of timber salvaged after a storm cannot be processed immediately and need to be safely stored. Millions of m3 were thus kept under water sprinkling after the recent storms in Europe (Bj€ orkhem et al., 1977; Jonsson, 2004). For example, in Sweden, the Byholma site sheltered one ow and Schroeder, 2008), and million m3 in 2007 (Lindel€ more than 6.5 million m3 were stored under sprinkling water in France between 1999 and 2001 (Figure 15.3) (Flot and Vautherin, 2002; Moreau et al., 2006). These massive salvage-logging and storage operations require equally massive logistics. A European lorry carries on average 30 m3 of timber. To fill a one million m3 storage unit such as the Byholma site mentioned above, more than 33,300 such lorry loads are necessary. Supposing that 50 lorries could be operated daily, about 670 days (almost 2 years) of uninterrupted work (logging and transportation) are necessary, with the consequence that timely removal of vulnerable material from the stands is not always feasible. In addition, the water storage of conifer logs raises environmental problems, as phenols and diterpene resin acids leak into the soil or the aquatic ecosystems (Jonsson, 2004; Hedmark et al., 2009). Spatially explicit damage assessment is an extremely important issue regarding I. typographus, since salvage logging is the preferred option to prevent further damage. Pest monitoring is intensively carried out in many countries. For example, in Switzerland (WSL—Forest Protection Overviews, 2014) and Austria (Bundesforschungszentrum fu¨r Wald, 2014), yearly damage reports fed by a network of local observers are available online. In France, a similar database is kept centrally (De´partement de la Sante´ des Foreˆts, 2014). The same situation exists in the Belgian

Walloon region (Observatoire wallon de la Sante´ des Foreˆts, 2014). One difficulty in these assessments is that they rely upon forest inventories, which even in the best cases are not totally accurate because some forest officers tend to overestimate or underestimate damage (Franklin et al., 2004). Based on the issues discussed above, risk planning is an extremely important component in the politics of I. typographus management. Enormous progress has been made recently in risk modeling (Table 15.2), for immediate and local use, as well as on a more prospective level, for long-term planning in view of climate change. Among the drivers that are recurrently identified in these models are the previous year’s volume of windthrows and volume of attacked timber, as well as the local volume of standing trees. A second “political” element of long-term planning could concern, whenever possible, the choice of the species selected for reforestation. In general terms, forest tree diversity reduces herbivory in oligophagous animal species (Jactel and Brockerhoff, 2007). More specifically, Warze´e et al. (2006), analyzing the relationships between I. typographus and the predatory clerid beetle, Thanasimus formicarius L. in northeastern France, caught a much higher predator/prey ratio (many more predators and less prey) in spruce stands mixed with pines than in pure spruce stands. They attributed this difference to the higher reproductive success of T. formicarius when it can pupate in the thicker bark of pines. A third aspect that relates to politics is the quarantine dimension, i.e., the set of rules and practices designed to prevent the pest from entering new areas. Within Europe, I. typographus outbreaks seem to happen only in areas where the insects have been long established. Recolonizing Eurasia after the glaciations, Norway spruce (Picea abies (L.)) has spread naturally only in higher elevations and latitudes (Taberlet et al., 1998; EUFORGEN, 2009). During the last 150 years, however, it has been widely planted

Economics and Politics of Bark Beetles Chapter 15

outside of this limited range. At the same time, Picea sitchensis (Bong.) Carrie`re was also introduced in Europe from northwestern America. Ips typographus has followed its ancient and new hosts into these new territories, but with a time lag. In Belgium, for example, P. abies plantations started around 1885 (Scheepers et al., 1997), and I. typographus colonized the country quite slowly afterwards. In the early 1970s, it was largely established in the country (Dourojeanni, 1971), but at densities too low for causing outbreaks. The first outbreaks only appeared in 1976 (J.C. Gre´goire, pers. observ.), during an exceptionally hot, dry summer (IRM, 2014). Some northwestern, lower elevation parts of France (Normandy, Brittany), also recently planted, are still under colonization. The beetles are present and occasionally colonize windthrows (Gilbert et al., 2005), but never reach outbreak level, suggesting that an Allee threshold has not yet been reached (Liebhold and Tobin, 2008), in spite of the heavy commercial movements of spruce roundwood, sometimes infested, within Europe or from outside the European Union (Piel et al., 2006, 2008). This is probably also an important reason why it has never established in the USA or New Zealand, where it is listed as a quarantine pest, although it is regularly intercepted. Ips typographus was found 286 times at US ports between 1985 and 2000 (Haack, 2001), and constituted 6% of all bark beetles intercepted in New Zealand between 1950 and 2000 (Brockerhoff et al., 2006). In the European Union, special provisions in the phytosanitary rules (Commission Directive, 2008) grant to Great Britain and Ireland the status of “Protected Zones” that allow these countries, free so far from I. typographus, to restrict intra-European Union commercial movements of coniferous logs and timber.

4.2 A Deadly Mistake, but for Which Party?—Secondary Ambrosia Beetles Attacking Living Beech in Europe The ambrosia beetles Trypodendron domesticum (L.) and Trypodendron signatum (F.) are known as secondary species, attacking dying or dead broadleaved trees to which they are attracted by volatiles (e.g., ethanol) produced in the trees’ fermenting tissues (Kerck, 1972; Holighaus and Schu¨tz, 2006). In the early 2000s, however, these species attacked standing beech trees (Fagus sylvatica L.) in Belgium, Germany, France, and Luxemburg, affecting more than 1.8 million m3 (Eisenbarth et al., 2001; Huart et al., 2003; Arend et al., 2006). The first symptoms, observed in 1999, were not very surprising, as they were concentrated around necrotic areas dating from the winter 1998–1999 and probably related to frost damage (Huart et al., 2003). In the following years, however, these insects attacked areas on apparently healthy trees. Three

601

Ophiostoma species were found in the galleries: O. quercus (Georgev.) Nannf., O. bacillisporum (Butin and G. Zimm.) de Hoog and R. J. Scheff., and a new species, O. arduennense F.-X. Carlier, Decock, K. Jacobs and Maraite (Carlier et al., 2006). Several secondary fungi rapidly colonized the stems of some of the attacked trees. These included Fomes fomentarius (L.) Fr., Fomitopsis pinicola (Sw.) P. Karst., Stereum hirsutum (Willd.) Pers., and Trametes versicolor (L.) Lloyd) (La Spina et al., 2013). The breaking of whole trees or large branches raised serious safety issues for foresters, forest workers, hikers, and hunters, but the main consequence of this outbreak was economic. Valuable bolts that had been reserved for slicing and that were to be exported to China were embargoed because of the staining of the wood. It was even difficult to sell the wood for pulp, because of the rapid development of lignivorous fungi. As the timber market had decreased after the Lothar storm in December 1999, many owners had preferred to keep their stock standing, postponing any sale in hopes of an improved market, and found their assets seriously diminished. After 2002, the outbreak subsided and many trees recovered, sealing the often-aborted galleries under new wood. However, the remaining stands are still marked in the memory of sawyers, and very low prices are offered for the local timber. The losses were high for the forest market, as the remaining beetles attacked the standing trees, perished in their attempt to colonize these trees, but left stains in the wood. Similar, smaller outbreaks were observed in the past in Belgium (1929 and 1942) and in neighboring countries (Zycha, 1943; Prieels, 1961; Poncelet, 1965; Nageleisen, 1993), and other secondary ambrosia bark beetles have been observed to attack living trees in other parts of the world (Ku¨hnholz et al., 2001; Coyle et al., 2005). The causes of this phenomenon are still unknown. One hypothesis regarding the Belgian outbreak is that the early frost in the winter of 1998–1999 affected trees that were still physiologically unprepared. The trees were affected in two ways: direct frost necroses (explaining the first insect attacks in 1999) and longer-term damage (explaining the subsequent attacks on apparently healthy trees). La Spina et al. (2013) explored this hypothesis further by analyzing the Belgian weather records, and by direct experiments where they inflicted frost wounds to mature trees using dry ice. The meteorological records showed “very exceptional” (one occurrence in 56 years) cold waves 1 year before the outbreaks in 1929 and 1942, and an “exceptional” (one occurrence in 30 years) one in 1998. The field experiments carried out by La Spina et al. (2013) resulted in beetle attacks but, contrary to the field observations in 1999–2002, the galleries were limited to a heavily necrotic zone in the sapwood. Other hypotheses could be developed, such as adverse soil conditions (drought, waterlogging) and/or sublethal

602

Bark Beetles

attacks of pathogenic fungi could have weakened the trees and made them attractive to the insects. Ranger et al. (2010, 2013) induced ethanol production in potted trees submitted to flood-stress, which made them attractive to Xylosandrus germanus (Blandford). McPherson et al. (2001, 2008) observed ambrosia beetles attracted to and colonizing oaks infected by Phytophthora ramorum Werres, De Cock and Man in’t Veld, and Kelsey et al. (2013) showed that the infected trees produced ethanol that was attractive to ambrosia beetles. In Europe, Jung (2009) linked beech decline to infection by Phytophthora spp. In a survey of 49 sites in southern Belgium, Schmitz et al. (2009) found P. cambivora (Petri) Buisman and P. gonapodyides (H. E. Petersen) Buisman infecting living trees in 19 sites. Waterlogging and fungal infection could act jointly, as floodstress on the one hand reduces tree resistance and induces ethanol production, and on the other hand favors the production and propagation of the Phytophthora zoospores.

4.3 Fallen and Standing Alike— The Spruce Beetle in North America The spruce beetle D. rufipennis is widely distributed across North America (Chapter 8). It extends from central Alaska to Newfoundland and down the Rocky Mountains almost to Mexico (Wood, 1982). This beetle breeds in all Picea species within its range, although black spruce, P. mariana (Mill.) Britton, Sterns and Poggenburg, is rarely attacked, and susceptibility and suitability vary among other species (Werner et al., 2006a). The spruce beetle is associated with several species of fungi, most commonly Leptographium abietinum (Peck) M. J. Wingf. (Six and Bentz, 2003). This insect shows markedly different population dynamics in different regions, and hence poses very different levels and types of management concerns. Appropriate management tactics, and accompanying policy issues, vary accordingly. This diversity of impacts and behaviors also makes spruce beetle a useful model for understanding management options for bark beetles in general. Throughout much of its range, D. rufipennis is a truly eruptive species, capable of undergoing intermittent large-scale outbreaks. Landscape-scale outbreaks occur throughout coastal Alaska, British Columbia, and the northwestern USA and Rocky Mountains (Safranyik, 1988; Eisenhart and Veblen, 2000; Werner et al., 2006a). A large outbreak in central British Columbia resulted in mortality over 175,000 ha (Cozens, 1997). From 1920 to 1989, 847,000 ha of spruce forest in Alaska were impacted (Holsten, 1990). An outbreak from 1989 to 2004 in Alaska resulted in 1.2 million ha of affected spruce forests, with an estimated 30 million trees killed per year. More than 90% of trees >11 cm were killed in some stands (Werner et al., 2006a). These outbreaks completely transform the

structures and compositions of forests, converting them from predominantly spruce to either angiosperms, such as birch and aspen, conifers such as pine, hemlock or fir, and sometimes grasses, depending on location and the heterogeneity of the forest (Lewis and Lindgren, 2000; Boucher and Mead 2006; Werner et al., 2006a). Impacts include economic losses, wildlife habitat effects, hydrological changes, aesthetic value loss, and increased risk to humans due to danger trees and possibly catastrophic fire (Werner et al., 2006a). Outbreaks are commonly followed by increased populations of secondary bark beetles such as Ips spp., which can be problematic in residential areas. Spruce trees that are too small to support beetle development survive these outbreaks, forming the basis for an eventual return to spruce. Like other eruptive bark beetles, D. rufipennis outbreaks are relatively uncommon, and there are long intervening periods during which populations are low. During these endemic periods, populations are held within a relatively stable range by a combination of tree defense, resource availability, interspecific competition, predators, weather, and their interactions (Chapter 1). The release of D. rufipennis populations from endemic to eruptive dynamics is often associated with scattered windthrow events (Safranyik, 1985), in combination with stresses on host tree defense, such as drought (Hart et al., 2014), and abnormally high temperatures that increase the beetles’ overwintering survival and accelerate development (Werner et al., 1977; Werner and Holsten, 1985; Hansen and Bentz, 2003). This insect has a facultative diapause, and in regions where semivoltinism is common, responds to warm conditions by shifting to a univoltine life cycle, greatly increasing the likelihood of outbreaks (Hansen et al., 2001b). At high densities, however, populations of this insect become self-amplifying, as they successfully enter and overwhelm vigorous trees regardless of their defensive capabilities (Lewis and Lindgren, 2002; Wallin and Raffa, 2004; Raffa et al., 2008). Throughout much of its range, the spruce beetle never or rarely undergoes major outbreaks. The reasons vary with region, but further demonstrate how a combination of factors is required for an outbreak to occur (Raffa et al., 2008). In interior Alaska, populations are typically univoltine and the habitat consists of extensive tracts of Picea, two ingredients that foster outbreaks. However, spruce beetles there are almost entirely limited to windthrown or otherwise stressed trees. The reasons are not entirely clear, but interspecific competition appears much higher in interior than coastal Alaska, probably arising from the drier conditions, and hence drier phloem, that favor Ips spp. (Werner et al., 2006b). Likewise, throughout the Great Lakes region, D. rufipennis is almost entirely limited to highly stressed trees. Although populations there are univoltine, the forests are much more diverse than in the west,

Economics and Politics of Bark Beetles Chapter 15

4.4 A Political, Economic and Ecological Challenge—The Mountain Pine Beetle in British Columbia The mountain pine beetle D. ponderosae is without a doubt the most destructive bark beetle in North America (Safranyik and Carroll, 2006), and possibly the world. Large-scale eruptions have occurred with semi-regular frequency in western North America, averaging about 40 years in British Columbia (Alfaro et al., 2010). During the past decades, several outbreaks have occurred that have been characterized by increasing intensity and scale, with the most recent surpassing all others by a large margin (Westfall and Ebata, 2014; Petersen and Stuart, 2014). The result has been substantial ecological and socioeconomic impacts, even including a notable occurrence of allergies to air-borne mountain pine beetle allergens (Stark and Li, 2009), and an international court challenge to Canadian lumber pricing practices under the US-Canada Softwood Lumber Agreement (Woo, 2012; Petersen and Stuart, 2014). The impacts have been particularly notable in British Columbia, where the main host tree, lodgepole pine (Pinus contorta var. latifolia Engelm.), is one of the primary commercial conifer species. As of 2012, well over

one billion US dollars had been invested by provincial and federal governments to mitigate the impact of the outbreak, and about 700 million m3 of lodgepole pine had been killed (Ministry of Forests, Lands and Natural Resources Operations, 2012). Lodgepole pine is a highly adaptable species with a wide distribution in western North America (Forrest, 1980). It is a fast-growing seral conifer that occupies vast areas of the Central Plateau of British Columbia as a leading species. In areas with frequent fires, this species often persists as a climax species in even-aged monocultures because a high proportion of the population has serotinous cones that persist on trees for many years, only opening and releasing seed after exposure to heat (Lotan and Critchfield, 1990). Homogeneous, mature lodgepole pine stands in Tweedsmuir and Entiako Provincial Parks (British Columbia), and the lack of management in these areas, are frequently pointed to as the initial cause of the current outbreak (Gawalko, 2004), but Aukema et al. (2006) showed that outbreaks also started concurrently in many parts of British Columbia. In the absence of fire, lodgepole pine is susceptible to mountain pine beetle outbreaks, leading to complex, multi-layered stand structures (Axelson et al., 2009). In mixed species stands, lodgepole pine is eventually displaced by long-lived species like Picea, Pseudotsuga, and Abies spp., in part due to mountain pine beetle-caused mortality of pines older than 80 years. Taylor et al. (2006), using projections from 1990 inventory data, showed that the average age of lodgepole pine stands changed from 51 years in 1910 to 114 years in 2010, and the age distribution from 17% mountain-pine beetle susceptible trees to 56% (Figure 15.4). This change was due to increasingly effective fire protection and relatively low harvesting rates until the 1960s. The increase in availability of

Proportion of susceptible age classes (%)

which can dampen population responses to environmental perturbations. Further, interspecific competition, especially from Dryocoetes spp., is much more intense in the Midwest than west (Haberkern and Raffa, 2003; Raffa et al., in press). For example, a huge blowdown event in the Boundary Waters region of northern Minnesota raised concerns about subsequent spruce beetle outbreaks. Instead, a highly diverse subcortical community emerged (Gandhi et al., 2009) and large-scale outbreaks did not follow. Further, ratios of predator to tree-killing bark beetle populations appear to be relatively higher in midwestern than western forests (Raffa et al., in press), and predacious beetles in this region are strongly attracted to frontalin (Haberkern and Raffa, 2003), a component of the spruce beetle’s pheromone plume (Dyer, 1973). In this region, therefore, protection from spruce beetles need not be as proactive as in western North America, and remedial responses can be initiated after events such as spruce budworm, Choristoneura fumiferana (Clemens), outbreaks. In the eastern provinces of Canada and New England, spruce beetle appears more aggressive than in the Midwest, but less than in the west. Small, localized outbreaks may follow drought or outbreak by spruce budworm. However, these outbreaks do not appear to become self-sustaining on a landscape scale. The optimal strategy, then, is again one of careful monitoring, followed by sanitation where potential losses appear imminent, coupled with landscape-scale management of C. fumiferana.

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60%

53%

56%

49%

50% 35%

40% 26%

30%

20%

10%

17%

0% 1910

1930

1950

1970

1990

2010

Years FIGURE 15.4 Change over time of the proportion of susceptible age classes (90 to 150 cm DBH), following increasingly successful fire control. Redrawn from Taylor et al. (2006).

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susceptible hosts played a major role in driving the development of the current outbreak. Climate plays an important role in the population dynamics of mountain pine beetle (Chapter 13). Cold fall and winter temperatures, rather than host availability, have limited the latitudinal and elevational range of mountain pine beetle (Carroll et al., 2004). Significant increases in mean temperatures over the past few decades have reduced the occurrence of population-limiting cold events. Petersen and Stuart (2014) cite data indicating a 1.5
C increase of mean annual temperature from the mid-20th century and 10.4
C higher spring minimum temperatures from 1943 to 2008. Consequently, previously climatically unsuitable habitat for mountain pine beetle has now become suitable, generating conditions conducive to range expansion (Carroll et al., 2006; Cudmore et al., 2010; Safranyik et al., 2010; Cullingham et al., 2011), threatening sensitive whitebark pine (Pinus albicaulis Engelm.) ecosystems (Logan et al., 2010; Raffa et al., 2013), and impacting management (Konkin and Hopkins, 2009; Petersen and Stuart, 2014). After a large outbreak in the late 1980s, general strategies and tactics for bark beetle management (https://www. for.gov.bc.ca/tasb/legsregs/fpc/fpcguide/beetle/chap2.htm) were implemented under the Forest Practices Code of British Columbia Act. As of January 1, 2004, this prescriptive piece of legislation was replaced by the resultsbased Forest and Range Practices Act. Further legislative changes at the time of the initial population buildup of the current outbreak had a potentially negative impact on the ability of the British Columbia government to manage the most recent outbreak (Petersen and Stuart, 2014). Government oversight and staffing were reduced both in response to legislative changes and budget cuts, and this included the closure of many Regional Forest Service Offices in a number of small, resource-dependent communities, causing significant socioeconomic impact, which was further exacerbated in areas affected by the outbreak (Parfitt, 2010; Petersen and Stuart, 2014). The Federal Government of Canada provided funding for research and limited management activities through the Mountain Pine Beetle Initiative (Ministry of Forests, Lands and Natural Resources Operations, 2012; Petersen and Stuart, 2014). However, it is unlikely that the outbreak would have been stopped in a more favorable economic climate. Due to the uplift in annual allowable cut (AAC) and a focus on salvage of low-value beetle-killed pine (Burton, 2006; Petersen and Stuart, 2014) there has been a need to find alternate uses for the harvested pine. Dead pine may remain standing for many years, but loses value due to checking, staining, and decay (Lewis and Hartley, 2006; Lewis and Thompson, 2011). Consequently, other markets have been sought, e.g., utilization of dead wood for bioenergy (Kumar et al., 2008; Mahmoudi et al., 2009) or for

innovative products such as “Denim Pine” (Byrne et al., 2006) and “Beetlecrete” (Hopper, 2010). Further economic impact has been on recreation (McFarlane and Watson, 2008). There has also been concern about the potential impact on carbon sequestration (Kurz et al., 2008), although some studies in areas with advanced regeneration have indicated that they serve as carbon sinks due to increased sequestration by remaining live vegetation (Brown et al., 2010; Hansen, 2014). A pervasive paradigm has been that bark beetle outbreaks result in an increased risk of fire. However, recent studies indicated that climate is the primary determinant factor of wildfire frequency and intensity (Kulakowski and Jarvis, 2011; Simard et al., 2011). In a review, Page et al. (2014) questioned the validity of conclusions based on modeling, however. Due to the magnitude of the outbreak, there has been considerable concern over impacts on wildlife (ChanMcLeod, 2006; Ritchie, 2008; Saab et al., 2014). Bark insectivores, and particularly cavity nesters, appear to benefit initially (Martin et al., 2006; Norris and Martin, 2008; Drever et al., 2009; Saab et al., 2014), whereas populations of some other guilds, e.g., flickers (Colaptes auratus (L)) and red-naped sapsuckers (Sphyrapicus nuchalis Baird), decreased (Martin et al., 2006). Impacts on mammals varied (Saab et al., 2014). Direct impact on American marten (Martes americana (Turton)) populations may depend on management scenario (Steventon and Daust, 2009), although loss of primary prey species like American red squirrel (Tamiasciurus hudsonicus (Erxleben)) had a ripple effect, and fragmentation was negative for both marten and fisher (Martes pennanti (Erxleben)) populations due to their poor dispersal ability (Chan-McLeod, 2006). Ungulates are affected in different ways depending on habitat requirements (Chan-McLeod, 2006), with loss of cover being a primary driver. There is particular concern for impacts on caribou (Rangifer tarandus caribou (Gmelin)) with potential loss of habitat (Cichowski and Williston, 2005; McNay et al., 2008; Ritchie, 2008), including loss of terrestrial lichens and changes in snow accumulation patterns. Pacific salmon are indirectly impacted by the outbreak due to increasing water temperatures and altered hydrological cycles (Pacific Fisheries Resource Conservation Council, n.d.; Bewley et al., 2010).

4.5 A Chronic Presence—The Pine Engraver Across the Continent The pine engraver Ips pini (Say) has a transcontinental distribution across North America, and can utilize almost all Pinus and sometimes other genera within its range (Wood, 1982). With such a broad geographic and host species range, I. pini exemplifies the adaptive plasticity that bark beetles can show in their ecology, behavior, and

Economics and Politics of Bark Beetles Chapter 15

physiology with local biotic and abiotic conditions. Because of this plasticity, the socioeconomic impacts of this insect and optimal management approaches vary widely. In the western United States and Canada, I. pini coincides with several outbreak pine-killing species, such as D. ponderosae and D. brevicomis LeConte. In these regions, I. pini is largely a secondary insect, orienting to plant and insect volatiles emitting from trees attacked by the more aggressive species, or colonizing severely stressed trees either alone or in a scramble competition (Rankin and Borden, 1991; Safranyik et al., 1996). Throughout much of the west, I. pini is at least partially beneficial to humans, because it reduces reproductive success of primary bark beetles. For example, when D. ponderosae colonize fireinjured trees, competition with I. pini is one of the factors that limit its population increase (Powell et al., 2012). However, this competitive effect can be reduced somewhat, by vertical partitioning of the resource, whereby I. pini is often concentrated in the upper stems. Under some conditions, I. pini can be a pest in western forests, particularly during drought years or in highly dense stands (Kegley et al., 1997). During a chronic outbreak in Montana from 1974 to 1994 in ponderosa pine (Gara et al., 1999), slash management to promote rapid drying of host material was shown to be important. For example, how slash is distributed and treated, and how the equipment is used affects colonization rate, rate of drying, and prevalence of natural enemies (Six et al., 2002). The timing of thinning operations can be optimized to minimize population buildup (Gara et al., 1999). Finally, providing a “green chain,” i.e., providing a continuous supply of fresh slash during beetle flight, was recommended to prevent spillover attacks into live trees (Kegley et al., 1997) In the midwestern and northeastern portions of North America, there are no landscape-scale aggressive bark beetles that attack pine. In these regions, I. pini fills the niche of a primary, tree-killing species. However, the live trees this beetle selects almost always show at least moderate acute or chronic stress prior to attack. In the Great Lakes region, stress caused by belowground herbivory and accompanying root infection provide a continuous but limited source of susceptible trees (Klepzig et al., 1991). In plantations having high populations of these predisposing agents, I. pini can be problematic and sometimes requires direct control by sanitation or pheromone-based mass trapping. However, unlike aggressive species, I. pini populations do not become selfsustaining and encompass entire landscapes after an initial population increase. For example, during drought years, both the numbers of I. pini and the proportion of trees it kills that did not have prior root infection increase markedly. Unlike species such as D. ponderosae and D. rufipennis, after the drought subsides, I. pini populations again become restricted to trees with previously colonized roots or lower stems, and populations decline (Aukema et al., 2010). Reliance on such

605

a predictably and spatially concentrated resource as rootinfested trees appears to facilitate predator impacts (Erbilgin et al., 2002), but the spatial separation of plantations can inhibit predator dispersal to new infestations (Ryall and Fahrig, 2005). Ips pini also shows high plasticity in its pheromone chemistry. All I. pini produce ipsdienol, but local populations vary in the stereochemistry of their signals (Lanier et al., 1972, 1975; Miller et al., 1989). Most western populations produce almost entirely ()-ipsdienol. In contrast, midwestern and eastern populations produce blends that are either racemic or biased toward (+)-ipsdienol. Some areas of western Canada produce substantial amounts of (+)-ipsdienol. In addition to enantiomeric differences, midwestern and eastern populations produce lanierone, which is not attractive by itself, but greatly increases attraction to ipsdienol (Teale and Lanier, 1991; Miller et al., 1997). Western populations do not produce lanierone, although it is weakly to strongly synergistic to ()-ipsdienol in Arizona and Montana, and British Columbia, Canada (Miller et al., 1997; Steed and Wagner, 2008). Furthermore, populations in both Arizona and Montana had seasonal shifts in preference (Steed and Wagner, 2008). These patterns appear to arise from local selective pressures, specifically avoidance of interspecific competition with sympatric Ips (Birch et al., 1980; Borden et al., 1992), and escape from predators that exploit beetle pheromones in prey finding (Raffa and Dahlsten, 1995). That is, pheromone blends produced by I. pini differ from those of sympatric congenerics, which in the west include other species producing ipsdienol but in the midwest produce ipsenol. Likewise, local predators show mismatches from their prey in preferences for stereochemistry and derived components, suggesting time-lagged coevolution (Raffa et al., 2007). Regardless of their evolutionary origins, these variable mixtures, and the distinctions between local predator and prey preferences, provide opportunities to greatly improve both the efficacy and selectivity of pheromonally-based population monitoring and control methods (Dahlsten et al., 2003), but at the same time cause commercial challenges due to the need for locally specific blends, which increase cost of management. In addition to the above distinctions between eastern and western populations, I. pini also shows plasticity in its life history with latitude and elevation. It has an apparently facultative diapause, showing variation in cold tolerance and voltinism, both between regions and between years within regions (Lombardero et al., 2000). The number of generations per year can range from one to five depending on regional temperatures. This insect also shows plasticity in its overwintering behavior. In northern regions of the Midwest, it overwinters as adults in the soil. In other regions, it overwinters both during various life stages under the bark and as adults in soil.

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From a management perspective, knowledge of the population dynamics of I. pini, i.e., its responding to a resource pulse but not becoming self-driving, can be used to guide control strategies. Specifically, losses to this insect can be reduced by controlling the predisposing agents, by controlling I. pini directly, or both. This can involve tactics such as seasonally timing thinning operations to avoid infestation by lower-stem colonizing beetles such as D. valens, removing slash, sanitation clearing, or localized application of semiochemicals (Kegley et al., 1997). This contrasts with the eruptive bark beetle species, which can only be successfully managed by preventing initial population increases beyond a critical threshold. Thus, from a policy standpoint, I. pini does not necessitate coordinated actions on a large scale, but instead can be effectively addressed as needed by local private or government land managers.

5.

CONCLUSIONS

Bark beetles are important forest disturbance agents, reshaping whole landscapes and exerting a large variety of economic, environmental, and social impacts. Some of these impacts incur very high socioeconomic costs, while others exert positive influences on species richness and biodiversity. Although a substantial amount of information is available, and much practical and political knowledge has been developed, we are very far from mastering the “bark beetle ecosystem.” In the best of cases, we can to some extent anticipate or mitigate bark beetle impact where such actions are consistent with management objectives. Climate change and biological invasions are important threats against which satisfactory solutions, if any, remain to be found.

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