Unraveling the drivers of intensifying forest disturbance regimes in Europe

Natural disturbances like wildfire, windthrow and insect outbreaks are critical drivers of composition, structure and functioning of forest ecosystems. They are strongly climate‐sensitive, and are thus likely to be distinctly affected by climatic changes. Observations across Europe show that in recent decades, forest disturbance regimes have intensified markedly, resulting in a strong increase in damage from wind, bark beetles and wildfires. Climate change is frequently hypothesized as the main driving force behind this intensification, but changes in forest structure and composition associated with management activities such as promoting conifers and increasing standing timber volume (i.e. ‘forest change’) also strongly influence susceptibility to disturbances. Here, we show that from 1958 to 2001, forest change contributed in the same order of magnitude as climate change to the increase in disturbance damage in Europe's forests. Climate change was the main driver of the increase in area burnt, while changes in forest extent, structure and composition particularly affected the variation in wind and bark beetle damage. For all three disturbance agents, damage was most severe when conducive weather conditions and increased forest susceptibility coincided. We conclude that a continuing trend towards more disturbance‐prone conditions is likely for large parts of Europe's forests, and can have strong detrimental effects on forest carbon storage and other ecosystem services. Understanding the interacting drivers of natural disturbance regimes is thus a prerequisite for climate change mitigation and adaptation in forest ecosystem management.     

Influence of global warming on forest coleopteran communities with special reference to ambrosia and bark beetles

Forest insect pests are one of the major disturbance factors in forest ecosystems and their outbreaks are expected to be more severe under the influence of global warming. Coleopterans are dominant among forest insects and their ecological functions include general detritivores, dead wood feeders, fungivores, herbivores, live wood feeders and predators. Ambrosia and bark beetles contribute to ecological succession of forests and, therefore, ecological functions of forests can be changed in response to their outbreaks. Mountain pine beetle (MPB) outbreaks are the most dramatic example of changes in the ecological functions of forest due to the outbreak of a forest insect pest altered by global warming. Composition of coleopteran species varies with latitude. However, composition of functional groups is consistent with latitude which indicates that resources available to beetles are consistent. In coleopteran communities, ambrosia and bark beetles can become dominant due to increases of dead or stressed trees due to the warming climate. This can also induce changes in the ecological functions of coleopterans, i.e. selective force to displace trees that have lower ecological fitness due to temperature increase. Therefore, recent increases in the density ambrosia and bark beetles offer a chance to study ecological processes in forests under the influence of global warming.     

Factors influencing bark beetle outbreaks after forest fires on the Iberian Peninsula

Fires are among the most globally important disturbances in forest ecosystems. Forest fires can be followed by bark beetle outbreaks. Therefore, the dynamic interactions between bark beetle outbreaks and fire appear to be of general importance in coniferous forests throughout the world. We tested three hypotheses of how forest fires in pine ecosystems (Pinus pinaster Alton and P. radiata D. Don) in Spain could alter the population dynamics of bark beetles and influence the probability of further disturbance from beetle outbreaks: fire could affect the antiherbivore resin defenses of trees, change their nutritional suitability, or affect top-down controls on herbivore populations. P. radiata defenses decreased immediately after fire, but trees with little crown damage soon recovered with defenses higher than before. Fire either reduced or did not affect nutritional quality of phloem and either reduced or had no effect on the abundance, diversity, and relative biomass of natural enemies. After fire, bark beetle abundance increased via rapid aggregation of reproductive adults on scorched trees. However, our results indicate that for populations to increase to an outbreak situation, colonizing beetles must initiate attacks before tree resin defenses recover, host trees must retain enough undamaged phloem to facilitate larval development, and natural enemies should be sufficiently rare to permit high beetle recruitment into the next generation. Coincidence of these circumstances may promote the possibility of beetle populations escaping to outbreak levels.     

Climate change and the outbreak ranges of two North American bark beetles

Abstract

• 1 One expected effect of global climate change on insect populations is a shift in geographical distributions toward higher latitudes and higher elevations. Southern pine beetle Dendroctonus frontalis and mountain pine beetle Dendroctonus ponderosae undergo regional outbreaks that result in large‐scale disturbances to pine forests in the south‐eastern and western United States, respectively.
• 2 Our objective was to investigate potential range shifts under climate change of outbreak areas for both bark beetle species and the areas of occurrence of the forest types susceptible to them.
• 3 To project range changes, we used discriminant function models that incorporated climatic variables. Models to project bark beetle ranges employed changed forest distributions as well as changes in climatic variables.
• 4 Projected outbreak areas for southern pine beetle increased with higher temperatures and generally shifted northward, as did the distributions of the southern pine forests.
• 5 Projected outbreak areas for mountain pine beetle decreased with increasing temperature and shifted toward higher elevation. That trend was mirrored in the projected distributions of pine forests in the region of the western U.S. encompassed by the study.
• 6 Projected outbreak areas for the two bark beetle species and the area of occurrence of western pine forests increased with more precipitation and decreased with less precipitation, whereas the area of occurrence of southern pine forests decreased slightly with increasing precipitation.
• 7 Predicted shifts of outbreak ranges for both bark beetle species followed general expectations for the effects of global climate change and reflected the underlying long‐term distributional shifts of their host forests.

     

Large carbon release legacy from bark beetle outbreaks across Western United States

Warmer conditions over the past two decades have contributed to rapid expansion of bark beetle outbreaks killing millions of trees over a large fraction of western United States (US) forests. These outbreaks reduce plant productivity by killing trees and transfer carbon from live to dead pools where carbon is slowly emitted to the atmosphere via heterotrophic respiration which subsequently feeds back to climate change. Recent studies have begun to examine the local impacts of bark beetle outbreaks in individual stands, but the full regional carbon consequences remain undocumented for the western US. In this study, we quantify the regional carbon impacts of the bark beetle outbreaks taking place in western US forests. The work relies on a combination of postdisturbance forest regrowth trajectories derived from forest inventory data and a process‐based carbon cycle model tracking decomposition, as well as aerial detection survey (ADS) data documenting the regional extent and severity of recent outbreaks. We find that biomass killed by bark beetle attacks across beetle‐affected areas in western US forests from 2000 to 2009 ranges from 5 to 15 Tg C yr^?1 and caused a reduction of net ecosystem productivity (NEP) of about 6.1–9.3 Tg C y^?1 by 2009. Uncertainties result largely from a lack of detailed surveys of the extent and severity of outbreaks, calling out a need for improved characterization across western US forests. The carbon flux legacy of 2000–2009 outbreaks will continue decades into the future (e.g., 2040–2060) as committed emissions from heterotrophic respiration of beetle‐killed biomass are balanced by forest regrowth and accumulation.     

Anomalous outbreaks of an invasive defoliator and native bark beetle facilitated by warm temperatures,changes in precipitation and interspecific interactions

Biotic disturbance agents such as insects can be highly responsive to climatic change and have widespread ecological and economic impacts on forests. Quantifying the responses of introduced and native insects to climate, including how dynamics of one agent may mediate those of another, is important for forecasting disturbance and associated impacts on forest structure and function. We investigated drivers of outbreaks by larch casebearer Coleophora laricella, an invasive defoliator, and eastern larch beetle Dendroctonus simplex, a native, tree‐killing bark beetle, on tamarack Larix laricina from 2000 to in Minnesota, USA. We evaluated the utility of temporal, spatial and climatic variables in predicting the presence/absence of outbreaks of each insect in cells of rasterized aerial survey data. The role of defoliation by larch casebearer in outbreaks of eastern larch beetle was also investigated. For both species, the most important predictors of outbreak occurrence were proximity of conspecific outbreaks in space and time. For larch casebearer, outbreak occurrence was positively associated with spring precipitation and warmer growing seasons. Outbreak occurrence of eastern larch beetle was positively associated with warmer and dryer years and was more likely in cells with prior defoliation by larch casebearer. Our results demonstrate that climate can drive large scale outbreaks of introduced and non‐native disturbance agents on a single host species, and that interactions at the tree level between such agents may scale up to manifest across large temporal and spatial scales.     

Climate change induces multiple risks to boreal forests and forestry in Finland: A literature review

Climate change induces multiple abiotic and biotic risks to forests and forestry. Risks in different spatial and temporal scales must be considered to ensure preconditions for sustainable multifunctional management of forests for different ecosystem services. For this purpose, the present review article summarizes the most recent findings on major abiotic and biotic risks to boreal forests in Finland under the current and changing climate, with the focus on windstorms, heavy snow loading, drought and forest fires and major insect pests and pathogens of trees. In general, the forest growth is projected to increase mainly in northern Finland. In the south, the growing conditions may become suboptimal, particularly for Norway spruce. Although the wind climate does not change remarkably, wind damage risk will increase especially in the south, because of the shortening of the soil frost period. The risk of snow damage is anticipated to increase in the north and decrease in the south. Increasing drought in summer will boost the risk of large‐scale forest fires. Also, the warmer climate increases the risk of bark beetle outbreaks and the wood decay by Heterobasidion root rot in coniferous forests. The probability of detrimental cascading events, such as those caused by a large‐scale wind damage followed by a widespread bark beetle outbreak, will increase remarkably in the future. Therefore, the simultaneous consideration of the biotic and abiotic risks is essential.     

Radiative forcing of natural forest disturbances

Forest disturbances are major sources of carbon dioxide to the atmosphere, and therefore impact global climate. Biogeophysical attributes, such as surface albedo (reflectivity), further control the climate‐regulating properties of forests. Using both tower‐based and remotely sensed data sets, we show that natural disturbances from wildfire, beetle outbreaks, and hurricane wind throw can significantly alter surface albedo, and the associated radiative forcing either offsets or enhances the CO₂ forcing caused by reducing ecosystem carbon sequestration over multiple years. In the examined cases, the radiative forcing from albedo change is on the same order of magnitude as the CO₂ forcing. The net radiative forcing resulting from these two factors leads to a local heating effect in a hurricane‐damaged mangrove forest in the subtropics, and a cooling effect following wildfire and mountain pine beetle attack in boreal forests with winter snow. Although natural forest disturbances currently represent less than half of gross forest cover loss, that area will probably increase in the future under climate change, making it imperative to represent these processes accurately in global climate models.     

A Decade of Streamwater Nitrogen and Forest Dynamics after a Mountain Pine Beetle Outbreak at the Fraser Experimental Forest,Colorado

Forests of western North America are currently experiencing extensive tree mortality from a variety of bark beetle species, and insect outbreaks are projected to increase under warmer, drier climates. Unlike the abrupt biogeochemical changes typical after wildfire and timber harvesting, the outcomes of insect outbreaks are poorly understood. The mountain pine bark beetle (Dendroctonus ponderosae) began to attack lodgepole pine (Pinus contorta) at the Fraser Experimental Forest in 2002 and spread throughout the research area by 2007. We compared streamwater nitrogen (N) from 2003 through 2012 with data from the previous two decades in four watersheds with distinct forest management histories, stand structures, and responses to the beetle outbreak. Watersheds dominated by old-growth had larger trees and lost 85% of overstory pine and 44% of total basal area to bark beetles. In contrast, managed watersheds containing a mixture of second-growth (30–60 year old) and old-growth (250- to 350-year old) had higher density of subcanopy trees, smaller mean tree diameter, and lower bark beetle-induced mortality (~26% of total basal area). Streamwater nitrate concentrations were significantly higher in old-growth watersheds during the outbreak than pre-outbreak levels during snowmelt and base flow seasons. In mixed-age stands, streamwater nitrate concentrations were unaffected by the outbreak. Beetle outbreak elevated inorganic N export 43 and 74% in two old-growth watersheds though the amounts of N released in streamwater were low (0.04 and 0.15 kg N ha^?1) relative to atmospheric inputs (<2% of annual N deposition). Increased height, diameter, and foliar N of measured in residual live trees augmented demand for N, far in excess of the change in N export during the outbreak. Reallocation of soil resources released after pine mortality to overstory and understory vegetation helps explain high nutrient retention in watersheds affected by bark beetle outbreaks.     

The European spruce bark beetle <Emphasis Type="Italic">Ips typographus</Emphasis> in a national park: from pest to keystone species

The influence of natural disturbance on biodiversity is poorly known in the intensively cultivated landscape of Europe. As an example of insect disturbance we studied effects of gaps generated by outbreaks of the spruce bark beetle (Ips typographus) on biodiversity in the area of the National Park “Bavarian Forest” and compared them with openings (e.g. meadows) created by humans in these forests. Insects were sampled using flight interception traps across twelve ecotones between edges of closed forest, six bark beetle gaps and six meadows. The diversity and species density of true bugs and of bees/wasps increased significantly from the closed stand to the edge, and continued to increase inside the openings at interior and exterior edges. Species density in saproxylic beetles also increased significantly from closed forest to opening, but only across ecotones including bark beetle gaps. Similarly, the number of critically endangered saproxylic beetles increased significantly in bark beetle gaps. Using indicator species analysis a total of 60 species were identified as possessing a statistically significant value indicating preference for one of the habitat types along the ecotones: 29 of them preferred gaps, 24 preferred meadows, three were characteristic for edges of meadows, three for edges of bark beetle gaps, but only one was typical of closed forest. Most of our results support the thesis that I. typographus fulfils the majority of criteria for a keystone species, particularly that of maintenance of biodiversity in forests. Our results emphasize the value for the study and conservation of insect diversity of the policy of non-interference with natural processes pursued in some protected areas. As a recommendation to forest management for increasing insect diversity even in commercial forest, we suggest that logging in recent gaps in medium aged mixed montane stands should aim at retention of a part of the dead wood. Planting should be avoided, to lengthen the important phase of sunlit conditions.     

Climate drivers of bark beetle outbreak dynamics in Norway spruce forests

Bark beetles are among the most devastating biotic agents affecting forests globally and several species are expected to be favored by climate change. Given the potential interactions of insect outbreaks with other biotic and abiotic disturbances, and the potentially strong impact of changing disturbance regimes on forest resources, investigating climatic drivers of destructive bark beetle outbreaks is of paramount importance. We analyzed 17 time‐series of the amount of wood damaged by Ips typographus, the most destructive pest of Norway spruce forests, collected across 8 European countries in the last three decades. We aimed to quantify the relative importance of key climate drivers in explaining timber loss dynamics, also testing for possible synergistic effects. Local outbreaks shared the same drivers, including increasing summer rainfall deficit and warm temperatures. Large availability of storm‐felled trees in the previous year was also strongly related to an increase in timber loss, likely by providing an alternative source of breeding material. We did not find any positive synergy among outbreak drivers. On the contrary, the occurrence of large storms reduced the positive effect of warming temperatures and rainfall deficit. The large surplus of breeding material likely boosted I. typographus population size above the density threshold required to colonize and kill healthy trees irrespective of other climate triggers. Importantly, we found strong negative density dependence in I. typographus that may provide a mechanism for population decline after population eruptions. Generality in the effects of complex climatic events across different geographical areas suggests that the large‐scale drivers can be used as early warning indicators of increasing local outbreak probability.     

Significant increase in natural disturbance impacts on European forests since 1950

Over the last decades, the natural disturbance is increasingly putting pressure on European forests. Shifts in disturbance regimes may compromise forest functioning and the continuous provisioning of ecosystem services to society, including their climate change mitigation potential. Although forests are central to many European policies, we lack the long-term empirical data needed for thoroughly understanding disturbance dynamics, modeling them, and developing adaptive management strategies. Here, we present a unique database of >170,000 records of ground-based natural disturbance observations in European forests from 1950 to 2019. Reported data confirm a significant increase in forest disturbance in 34 European countries, causing on an average of 43.8 million m³ of disturbed timber volume per year over the 70-year study period. This value is likely a conservative estimate due to under-reporting, especially of small-scale disturbances. We used machine learning techniques for assessing the magnitude of unreported disturbances, which are estimated to be between 8.6 and 18.3 million m³/year. In the last 20 years, disturbances on average accounted for 16% of the mean annual harvest in Europe. Wind was the most important disturbance agent over the study period (46% of total damage), followed by fire (24%) and bark beetles (17%). Bark beetle disturbance doubled its share of the total damage in the last 20 years. Forest disturbances can profoundly impact ecosystem services (e.g., climate change mitigation), affect regional forest resource provisioning and consequently disrupt long-term management planning objectives and timber markets. We conclude that adaptation to changing disturbance regimes must be placed at the core of the European forest management and policy debate. Furthermore, a coherent and homogeneous monitoring system of natural disturbances is urgently needed in Europe, to better observe and respond to the ongoing changes in forest disturbance regimes.     

A model for the conquest of a tree by bark beetles

A model for the interaction between attacking bark beetles and a tree is developed and discussed. It is shown that in addition to the more intuitive outcomes where the tree wins or the beetles win, it is also deduced that under certain conditions there may exist a stable coexistence (at least for some period of time) between the beetles and a living tree. Finally, it is demonstrated that the outcome of the tree-beetle interaction often depends on initial conditions such as the number of colonizing beetles.
These results are discussed with reference to empirical findings, as well as to the development of proper population dynamics models for bark beetles in a forest stand, and models developed for assisting forest managers in avoiding bark beetle outbreaks and for minimizing the damage caused by a bark beetle outbreak.     

Influences of the biophysical environment on blister rust and mountain pine beetle,and their interactions,in whitebark pine forests

Aim To understand how the biophysical environment influences patterns of infection by non‐native blister rust (caused by Cronartium ribicola) and mortality caused by native mountain pine beetles (Dendroctonus ponderosae) in whitebark pine (Pinus albicaulis) communities, to determine how these disturbances interact, and to gain insight into how climate change may influence these patterns in the future. Location High‐elevation forests in south‐west Montana, central Idaho, eastern and western Oregon, USA. Methods Stand inventory and dendroecological methods were used to assess stand structure and composition and to reconstruct forest history at sixty 0.1‐ha plots. Patterns of blister rust infection and mountain pine beetle‐caused mortality in whitebark pine trees were examined using nonparametric Kruskal–Wallis ANOVA, Mann–Whitney U‐tests, and Kolmogorov–Smirnov two‐sample tests. Stepwise regression was used to build models of blister rust infection and mountain pine beetle‐related mortality rates based on a suite of biophysical site variables. Results Occurrence of blister rust infections was significantly different among the mountain ranges, with a general gradient of decreasing blister rust occurrence from east to west. Evidence of mountain pine beetle‐caused mortality was identified on 83% of all dead whitebark pine trees and was relatively homogenous across the study area. Blister rust infected trees of all ages and sizes uniformly, while mountain pine beetles infested older, larger trees at all sites. Stepwise regressions explained 64% and 58% of the variance in blister rust infection and beetle‐caused mortality, respectively, indicating that these processes are strongly influenced by the biophysical environment. More open stand structures produced by beetle outbreaks may increase the exposure of surviving whitebark pine trees to blister rust infection. Main conclusions Variability in the patterns of blister rust infection and mountain pine beetle‐caused mortality elucidated the fundamental dynamics of these disturbance agents and suggests that the effects of climate change will be complex in whitebark pine communities and vary across the species’ range. Interactions between blister rust and beetle outbreaks may accelerate declines or facilitate the rise of rust resistance in whitebark pine depending on forest conditions at the time of the outbreak.     

Natural disturbance impacts on ecosystem services and biodiversity in temperate and boreal forests

In many parts of the world forest disturbance regimes have intensified recently, and future climatic changes are expected to amplify this development further in the coming decades. These changes are increasingly challenging the main objectives of forest ecosystem management, which are to provide ecosystem services sustainably to society and maintain the biological diversity of forests. Yet a comprehensive understanding of how disturbances affect these primary goals of ecosystem management is still lacking. We conducted a global literature review on the impact of three of the most important disturbance agents (fire, wind, and bark beetles) on 13 different ecosystem services and three indicators of biodiversity in forests of the boreal, cool‐ and warm‐temperate biomes. Our objectives were to (i) synthesize the effect of natural disturbances on a wide range of possible objectives of forest management, and (ii) investigate standardized effect sizes of disturbance for selected indicators via a quantitative meta‐analysis. We screened a total of 1958 disturbance studies published between 1981 and 2013, and reviewed 478 in detail. We first investigated the overall effect of disturbances on individual ecosystem services and indicators of biodiversity by means of independence tests, and subsequently examined the effect size of disturbances on indicators of carbon storage and biodiversity by means of regression analysis. Additionally, we investigated the effect of commonly used approaches of disturbance management, i.e. salvage logging and prescribed burning. We found that disturbance impacts on ecosystem services are generally negative, an effect that was supported for all categories of ecosystem services, i.e. supporting, provisioning, regulating, and cultural services (P < 0.001). Indicators of biodiversity, i.e. species richness, habitat quality and diversity indices, on the other hand were found to be influenced positively by disturbance (P < 0.001). Our analyses thus reveal a ‘disturbance paradox’, documenting that disturbances can put ecosystem services at risk while simultaneously facilitating biodiversity. A detailed investigation of disturbance effect sizes on carbon storage and biodiversity further underlined these divergent effects of disturbance. While a disturbance event on average causes a decrease in total ecosystem carbon by 38.5% (standardized coefficient for stand‐replacing disturbance), it on average increases overall species richness by 35.6%. Disturbance‐management approaches such as salvage logging and prescribed burning were neither found significantly to mitigate negative effects on ecosystem services nor to enhance positive effects on biodiversity, and thus were not found to alleviate the disturbance paradox. Considering that climate change is expected to intensify natural disturbance regimes, our results indicate that biodiversity will generally benefit from such changes while a sustainable provisioning of ecosystem services might come increasingly under pressure. This underlines that disturbance risk and resilience require increased attention in ecosystem management in the future, and that new approaches to addressing the disturbance paradox in management are needed.     

Influence of temperature on spring flight initiation for southwestern ponderosa pine bark beetles (Coleoptera: Curculionidae, Scolytinae)

Determination of temperature requirements for many economically important insects is a cornerstone of pest management. For bark beetles (Coleoptera: Curculionidae, Scolytinae), this information can facilitate timing of management strategies. Our goals were to determine temperature predictors for flight initiation of three species of Ips bark beetles, five species of Dendroctonus bark beetles, and two genera of bark beetle predators, Enoclerus spp. (Coleoptera: Cleridae) and Temnochila chlorodia (Mannerheim) (Coleoptera: Ostomidae), in ponderosa pine forests of northcentral Arizona. We quantified beetle flight activity using data loggers and pheromone-baited funnel traps at 18 sites over 4 yr. Ambient air temperature was monitored using temperature data loggers located in close proximity to funnel traps. We analyzed degree-day accumulation and differences between minimum, average, and maximum ambient temperature for the week before and week of first beetle capture to calculate flight temperature thresholds. Degree-day accumulation was not a good predictor for initiation of beetle flight. For all species analyzed other than D. adjunctus Blandford, beetles were captured in traps only when springtime temperatures exceeded 15.0 degrees C. D. adjunctus was collected when maximum temperatures reached only 14.5 degrees C. Once initial flights had begun, beetles were often captured when maximum ambient air temperatures were below initial threshold temperatures. Maximum and average air temperatures were a better predictor for beetle flight initiation than minimum temperature. We establish a temperature range for effective monitoring of bark beetles and their predators, and we discuss the implications of our results under climate change scenarios.     

Investigating the abundance and flight period of bark beetles (Coleoptera: Curculionidae: Scolytinae) over elevational gradients in Sitka spruce forests

1. A warming climate, as predicted under current climate change projections, is likely to influence the population dynamics of many forest insect species. Numerous bark beetle species in both Europe and North America have already responded to a warming climate by significantly expanding their geographical ranges.
2. The aim of the current study was to investigate how populations of bark beetles within stands of Sitka spruce, a widely planted non-native commercial plantation tree species in the U.K., were likely to respond to a warming climate. Experimental plots were established in stands of Sitka spruce over elevational gradients in two commercial forest plantations, and the abundance and emergence times of key bark beetle species were assessed over a 3-year period using flight interception traps. The air temperature difference between the lowest and highest experimental plot in each forest was consistently >1°C throughout the 3-year period.
3. In general, the abundance of the most dominant bark beetle species (e.g. Trypodendron, Dryocoetes, Hylastes spp.) was higher, and emergence times tended to be earlier in the year at the lower elevation plots, where temperatures were higher, although not all bark beetle species responded in the same manner.
4. The results of the study indicated that, under the projected future climate warming scenarios, monoculture Sitka spruce stands at low elevations may potentially be more vulnerable to significant outbreak events from existing or invasive bark beetle species. Hence, consideration of establishing more resilient forests of Sitka spruce by diversifying the species composition and structure of Sitka spruce stands is discussed.

     

Stand‐replacing fires reduce susceptibility of lodgepole pine to mountain pine beetle outbreaks in Colorado

Aim As climate change is increasing the frequency, severity and extent of wildfire and bark beetle outbreaks, it is important to understand how these disturbances interact to affect ecological patterns and processes, including susceptibility to subsequent disturbances. Stand‐replacing fires and outbreaks of mountain pine beetle (MPB), Dendroctonus ponderosae, are both important disturbances in the lodgepole pine, Pinus contorta, forests of the Rocky Mountains. In the current study we investigated how time since the last stand‐replacing fire affects the susceptibility of the stand to MPB outbreaks in these forests. We hypothesized that at a stand‐scale, young post‐fire stands (< c. 100–150 years old) are less susceptible to past and current MPB outbreaks than are older stands. Location Colorado, USA. Methods We used dendroecological methods to reconstruct stand‐origin dates and the history of outbreaks in 23 lodgepole pine stands. Results The relatively narrow range of establishment dates among the oldest trees in most sampled stands suggested that these stands originated after stand‐replacing or partially stand‐replacing fires over the past three centuries. Stands were affected by MPB outbreaks in the 1940s/1950s, 1980s and 2000s/2010s. Susceptibility to outbreaks generally increased with stand age (i.e. time since the last stand‐replacing fire). However, this reduced susceptibility of younger post‐fire stands was most pronounced for the 1940s/1950s outbreak, less so for the 1980s outbreak, and did not hold true for the 2000s/2010s outbreak. Main conclusions Younger stands may not have been less susceptible to the most recent outbreak because: (1) after stands reach a threshold age of > 100–150 years, stand age does not affect susceptibility to outbreaks, or (2) the high intensity of the most recent outbreak reduces the importance of pre‐disturbance conditions for susceptibility to disturbance. If the warm and dry conditions that contribute to MPB outbreaks concurrently increase the frequency and/or extent of severe fires, they may thereby mitigate the otherwise increased landscape‐scale susceptibility to outbreaks. Potential increases in severe fires driven by warm and dry climatic trends may lead to a negative feedback by making lodgepole pine stands less susceptible to future MPB outbreaks.     

The suppression of Dendroctonus frontalis and subsequent wildfire have an impact on forest stand dynamics

Question: Interacting disturbance effects from Dendroctonus frontalis outbreaks and wildfire are thought to maintain Pinus spp. composition in the southeastern U. S. Our objective was to assess forest composition, structure, and succession following the interaction of two frequently occurring disturbance events in southern Pinus spp. forests: cut‐and‐leave suppression, a commonly used means for managing D. frontalis outbreaks, and wildfire. Location: Western Gulf Coastal Plain, Louisiana, USA. Method: Pinus taeda stands with cut‐and‐leave suppression and subsequent wildfire were compared to stands undisturbed by D. frontalis but with the same wildfire events twenty years after Pinus spp. mortality. The woody plant community was assessed in three different size classes and used to predict future forest types with the Forest Vegetation Simulator (50 years). Results: P. taeda is the most abundant (> 50%) species of saw‐ and poletimber‐sizes following cut‐and‐leave suppression with wildfire and in stands only with fire. Using canonical correspondence analysis, vegetation assemblages were primarily explained by slope position and elevation (7.6% variation explained). Fire intensity and stand age also accounted for variance in the ordination (4.4% and 3.1%, respectively). Dominant and co‐dominant P. taeda forest types were predicted by the model to be the most abundant forest types in each disturbance regime. In addition, new regeneration represents high hazard for future mortality from D. frontalis. Conclusion: Our study demonstrates that cut‐and‐leave suppression with additional wildfire disturbance maintains P. taeda composition, and does not alter forest composition differently from stands receiving only wildfire. As a result, predicted Pinus spp. basal area under both disturbances is great enough to facilitate future bark beetle disturbance.     

Response of ground and rove beetles (Coleoptera: Carabidae,Staphylinidae) to operational oil sands mine reclamation in northeastern Alberta,a case study

Species loss caused by anthropogenic disturbance threatens forest ecosystems globally. Until 50 years ago, the major sources of boreal forest disturbance in western Canada were a combination of forest wild fire events, pest insect outbreaks, and forest timber harvesting. However, in the 1960s, when the oil boom started in Alberta, oil and gas development along with oil sands mining quickly became another major forest disturbance agent. In this case study we report the effects of operational oil sands mine reclamation on terrestrial arthropod communities and compare them with nearby burned and mature forest sites as a way to provide a benchmark from which to understand the long-term trajectory of recovery for these groups. During the summer of 2016 over 6700 epigaeic beetles were collected using pitfall traps. A total of 43 species of ground beetles and 118 species of rove beetles were collected. Epigaeic beetle assemblages differed between the reclaimed, burned, and mature forest sites. Partitioning of beta diversity in the reclaimed, burned areas and mature forests indicated that species turnover formed the largest component of diversity. Species richness patterns were similar among sites; however, cluster analysis indicated that epigaeic beetle assemblages were only 20% similar between the reclaimed and natural sites. Although ground beetles of the reclaimed area showed positive spatial autocorrelation among treatments, both ground and rove beetles showed responses to the reclamation treatments. The reclaimed areas were dominated by small- to medium-sized open-habitat eurytopic species, whereas the fire and mature forest sites were dominated by larger forest species. The reclaimed area of this case study constitutes a novel, reconstructed ecosystem that is clearly not equivalent in species assemblage to burnt stands of similar age or to mature forest stands.