Phenological synchrony between eastern spruce budworm and its host trees increases with warmer temperatures in the boreal forest

Seasonality of forest insects: why diapause matters

Insects have major impacts on forest ecosystems, from herbivory and soil-nutrient cycling to killing trees at a large scale. Forest insects from temperate, tropical, and subtropical regions have evolved strategies to respond to seasonality; for example, by entering diapause, to mitigate adversity and to synchronize lifecycles with favorable periods. Here, we show that distinct functional groups of forest insects; that is, canopy dwellers, trunk-associated species, and soil/litter-inhabiting insects, express a variety of diapause strategies, but do not show systematic differences in diapause strategy depending on functional group. Due to the overall similarities in diapause strategies, we can better estimate the impacts of anthropogenic change on forest insect populations and, consequently, on key ecosystems.

Complementary roles of two classes of defense chemicals in white spruce against spruce budworm

MAIN CONCLUSION

Monoterpenes and phenolics play distinct roles in defending white spruce trees from insect defoliators. Monoterpenes contribute to the toxicity of the foliage, deterring herbivory, whereas phenolics impede budworm growth. This study demonstrates the complex interplay between monoterpenes and phenolics and their collective influence on the defense strategy of white spruce trees against a common insect defoliator. Long-lived coniferous trees display considerable variations in their defensive chemistry. The impact of these defense phenotype variations on insect herbivores of the same species remains to be thoroughly studied, mainly due to challenges in replicating the comprehensive defense profiles of trees under controlled conditions. This study methodically examined the defensive properties of foliar monoterpenes and phenolics across 80 distinct white spruce families. These families were subsequently grouped into two chemotypes based on their foliar monoterpene concentrations. To understand the separate and combined effects of these classes on tree defenses to the eastern spruce budworm, we conducted feeding experiments using actual defense profiles from representative families. Specifically, we assessed budworm response when exposed to substrates amended with phenolics alone or monoterpenes. Our findings indicate that the ratios and amounts of monoterpenes and phenolics present in the white spruce foliage influence the survival of spruce budworms. Phenotypes associated with complete larval mortality exhibited elevated ratios (ranging from 0.4 to 0.6) and concentrations (ranging from 1143 to 1796 ng mg-1) of monoterpenes. Conversely, families characterized by higher phenolic ratios (ranging from 0.62 to 0.77) and lower monoterpene concentrations (ranging from 419 to 985 ng mg-1) were less lethal to the spruce budworm. Both classes of defense compounds contribute significantly to the overall defensive capabilities of white spruce trees. Monoterpenes appear critical in determining the general toxicity of foliage, while phenolics play a role in slowing budworm development, thereby underscoring their collective importance in white spruce defenses.

Climate-driven shifts in leaf senescence are greater for boreal species than temperate species in the Acadian Forest region in contrast to leaf emergence shifts

The Acadian Forest Region is a temperate-boreal transitional zone in eastern North America which provides a unique opportunity for understanding the potential effects of climate change on both forest types. Leaf phenology, the timing of leaf life cycle changes, is an important indicator of the biological effects of climate change, which can be observed with stationary timelapse cameras known as phenocams. Using four growing seasons of observations for the species Acer rubrum (red maple), Betula papyrifera (paper/white birch) and Abies balsamea (balsam fir) from the Acadian Phenocam Network as well as multiple growing season observations from the North American PhenoCam Network we parameterized eight leaf emergence and six leaf senescence models for each species which span a range in process and driver representation. With climate models from the Fifth Phase of the Coupled Model Intercomparison Project (CMIP5) we simulated future leaf emergence, senescence and season length (senescence minus emergence) for these species at sites within the Acadian Phenocam Network. Model performances were similar across models and leaf emergence model RMSE ranged from about 1 to 2 weeks across species and models, while leaf senescence model RMSE ranged from about 2 to 4 weeks. The simulations suggest that by the late 21st century, leaf senescence may become continuously delayed for boreal species like Betula papyrifera and Abies balsamea, though remain relatively stable for temperate species like Acer rubrum. In contrast, the projected advancement in leaf emergence was similar across boreal and temperate species. This has important implications for carbon uptake, nutrient resorption, ecology and ecotourism for the Acadian Forest Region. More work is needed to improve predictions of leaf phenology for the Acadian Forest Region, especially with respect to senescence. Phenocams have the potential to rapidly advance process-based model development and predictions of leaf phenology in the context of climate change.

Management Implications for the Nantucket Pine Tip Moth From Temperature-Induced Shifts in Phenology and Voltinism Attributed to Climate Change

Forest insect pest phenology and infestation pressure may shift as temperatures continue to warm due to climate change, resulting in greater challenges for sustainable forest management . The Nantucket pine tip moth (NPTM) (Rhyacionia frustrana Comstock) (Lepidoptera: Tortricidae) is a native forest regeneration pest in the southeastern U.S. with multiple generations per year. Changes in NPTM voltinism may result from temperature-induced shifts in NPTM phenology. Degree-day models have been used to develop optimal spray dates (OSDs) for NPTM. The 2000 Spray Timing Model (STM), based on temperature data from 1960 to 2000, provided generation-specific 5-d OSDs to effectively time applications of contact insecticides. An updated degree-day model, the 2019 STM, is based on temperature data from 2000 to 2019 and was used to detect changes in voltinism as well as shifts in phenology and OSDs. Based on the model, increased voltinism occurred at 6 of the 28 study locations (21%). Changes in voltinism occurred in the Piedmont and Coastal Plain of Georgia, U.S., with shifts from three to four or four to five generations a year, depending on location. The OSDs from the 2019 STM were compared to the 2000 STM OSDs. Over half (57%) of the OSDs differed by 5-15 d, with the majority (66%) resulting in earlier spray dates. The 2019 STM will help growers adapt NPTM control tactics to temperature-induced phenology shifts. NPTM serves as an example of temperature-induced changes attributed to climate change in a forest insect pest with important implications to forest management.

Pine processionary moth outbreaks cause longer growth legacies than drought and are linked to the North Atlantic Oscillation

Climatic warming is assumed to expand the geographic range of insect pests whose distribution is mainly constrained by low temperatures. This is the case of the pine processionary moth (Thaumetopoea pityocampa), which is one of the main conifer defoliators in the Mediterranean Basin. Warmer winters may lead to a northward/upward expansion of this insect, as short-term studies have shown. However, no long-term data, i.e. spanning at least one century, has been used to examine these projections. We test the hypotheses that climatic warming (i) has caused an upward shift of the pine processionary moth, and (ii) has increased the frequency of severe defoliations. We used dendrochronological methods to reconstruct defoliations over the period 1900-2006 in 14 sites spanning a wide altitudinal range (1070-1675 m) in Teruel, eastern Spain. We built local ring-width chronologies for four co-occurring pine species with different degree of susceptibility against the moth defoliations, from highly suitable or palatable species (Pinus nigra) to moderately (Pinus sylvestris, Pinus halepensis) or rarely defoliated species (Pinus pinaster). We validated the tree-ring reconstructions of outbreaks using a field record of stand defoliations spanning the period 1971-2006. Outbreaks in the most affected P. nigra stands corresponded to abrupt one- to two-year growth reductions (70-90% growth loss). Reconstructed outbreaks occurred on average every 9-14 years. The growth memory of outbreaks was weaker but lasted longer (1-6 years) than that due to droughts (1-3 years). Neither an upward expansion nor an increase in outbreak frequency was observed. Severe PPM defoliations did not increase as climate warmed, rather they were positively related to the winter North Atlantic Oscillation.

Abundance and Distribution of Foliage on Balsam Fir and White Spruce in Reference to Spruce Budworm Ecology and Absolute Population Density Estimation

We describe the distribution and amount of foliage, expressed as foliated branch surface area, weight, or number of buds in the live crown of healthy open-grown and closed-canopy balsam fir and white spruce trees. Balsam fir and white spruce have very similar total foliage surface area and weight. The live crown of white spruce trees contains fewer buds than balsam fir of similar dimensions. Thus, bud density per unit foliage weight or surface area is higher in balsam fir than in white spruce. We also observed that buds tend to grow in clusters more often on balsam fir than on white spruce, and that larvae of the spruce budworm preferentially attack buds that grow in clusters. Equations were developed to predict the total surface area and weight of foliage as well as number of buds in the live crown for estimation of absolute population density of spruce budworm. These equations use diameter at breast height (DBH) and the number of nodes in the live crown as predictors. When data on the number of live nodes are unavailable, it can be estimated from tree height. Equations were also developed from which to estimate foliage area, weight or bud numbers from DBH only.

Quantifying and predicting population connectivity of an outbreaking forest insect pest

Context

Dispersal has a key role in the population dynamics of outbreaking species such as the spruce budworm (Choristoneura fumiferana) as it can synchronize the demography of distant populations and favor the transition from endemic to epidemic states. However, we know very little about how landscape structure influences dispersal in such systems while such knowledge is essential for better forecasting of spatially synchronous population dynamics and to guide management strategies.

Objectives

We aimed to characterize the spatial environmental determinants of spruce budworm dispersal to determine how these features affect outbreak spread in Quebec (Canada). We then apply our findings to predict expected future landscape connectivity and explore its potential consequences on future outbreaks.

Methods

We used a machine-learning landscape genetics approach on 447 larvae covering most of the outbreak area and genotyped at 3562 SNP loci to identify the main variables affecting connectivity.

Results

We found that the connectivity between outbreak populations was driven by the combination of precipitation and host cover. Our forecasting suggests that between the current and next outbreaks, connectivity may increase between Ontario and Quebec, and might decrease in the eastern part, which could have the effect of limiting outbreak spread from Ontario and Quebec to the eastern provinces.

Conclusions

Although we did not identify any discrete barriers, low connectivity areas might constrain dispersal in the current and future outbreaks and should in turn, be intensively monitored. However, continued sampling as the outbreak progresses is needed to confirm the temporal stability of the observed patterns.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10980-021-01382-9.

Limited increase in asynchrony between the onset of spring green-up and the arrival of a long-distance migratory bird

For many migrant bird species around the world, climate change has been shown to induce changes in the timings of arrival and the onset of spring food availability at breeding sites. However, whether such changes enlarged asynchrony between the timings of spring arrival of long-distance migratory birds and onset of vegetation greenness increase remain controversial. We used a 29-year phenological dataset to investigate the temporal changes in spring first-sighting date (FSD) of a long-distance migratory bird (barn swallow, Hirundo rustica), from observations at 160 local breeding sites across northern China, and the vegetation green-up onset date (VGD), determined from satellite observations of vegetation greenness. We found that both FSD and VGD trended earlier at over two-thirds of the breeding sites. FSD significantly advanced at 26.9% of the sites, and VGD significantly advanced at 23.8% of the sites. The degree of asynchrony between FSD and VGD changed significantly at one-third of the breeding sites (22.5% with an increase versus 11.3% with a decrease), leading to a limited increase of phenological mismatch. We speculated that climate change did not disrupt the climatic connections between most breeding sites and corresponding non-breeding sites (wintering grounds and migration routes). Our findings suggest that climate change may not greatly increase phenological mismatch between first arrival date of barn swallows and VGD at breeding sites. Importantly, this study should serve as a cue to encourage ecologists and conservation biologists to expand the context under which to explore the ecological consequences of phenological shifts beyond asynchrony, such as individual survival, population demography and ecosystem-level consequences.

Landscape-scale population connectivity in two parasitoid species associated with the spruce budworm: Testing the birdfeeder effect using genetic data

Periodic and spatially synchronous outbreaks of insect pests have dramatic consequences for boreal and sub-boreal forests. Within these multitrophic systems, parasitoids can be stabilizing agents by dispersing toward patches containing higher host density (the so-called birdfeeder effect). However, we know little about the dispersal abilities of parasitoids in continuous forested landscapes, limiting our understanding of the spatiotemporal dynamics of host-parasitoid systems, and constraining our ability to predict forest resilience in the context of global changes. In this study, we investigate the spatial genetic structure and spatial variation in genetic diversity of two important species of spruce budworm larval parasitoids during outbreaks: Apanteles fumiferanae Viereck (Braconidae) and Glypta fumiferanae (Viereck) (Ichneumonidae). Using parasitoids sampled in 2014 from 26 and 29 locations across a study area of 350,000 km² , we identified 1,012 and 992 neutral SNP loci for A. fumiferanae (N = 279 individuals) and G. fumiferanae (N = 382), respectively. Using DAPC, PCA, AMOVA, and IBD analyses, we found evidence for panmixia and high genetic connectivity for both species, matching the previously described genetic structure of the spruce budworm within the same context, suggesting similar effective dispersal during outbreaks and high parasitoid population densities between outbreaks. We also found a significant negative relationship between genetic diversity and latitude for A. fumiferanae but not for G. fumiferanae, suggesting that northern range limits may vary by species within the spruce budworm parasitoid community. These spatial dynamics should be considered when predicting future insect outbreak severities in boreal landscapes.

Improved performance of the eastern spruce budworm on black spruce as warming temperatures disrupt phenological defences

Phenological shifts, induced by global warming, can lead to mismatch between closely interacting species. The eastern spruce budworm, Choristoneura fumiferana, an important outbreaking insect defoliator in North America, mainly feeds on balsam fir, Abies balsamea, which has historically been well synchronized with the insect. But as climate change pushes the northern range limit of the budworm further north into the boreal forest, the highly valuable black spruce, Picea mariana, historically protected against the budworm by its late budburst phenology, is suffering increased defoliation during the current outbreak. We tested the hypothesis that rising temperatures can lead, not to a mismatch, but to an improved match between the budworm and black spruce through differential phenological advancement. For 3 years, eastern spruce budworm larvae were reared from instar 2 to pupae, on both black spruce and balsam fir, in a temperature free-air controlled enhancement experiment (T-FACE) consisting in 24 field plots, half of which were heated at +2°C from March to October. Our results show that every year, larval development was faster on heated trees and pupation was earlier than on unheated trees. Bud development was also accelerated in heated trees of both species. However, there was no difference in mass between pupae that developed at +2°C and controls at the end of the season. Finally, we found no difference either in development rate or pupal mass between larvae reared on black spruce and those reared on balsam fir. This suggests that under higher temperature regimes, eastern spruce budworm will be as successful on black spruce as on balsam fir, as black spruce budburst becomes better synchronized with the insect's emergence from diapause. This could lead to critical changes in outbreak dynamics and severity with important ecological state shifts at the landscape level.

Phenological sensitivity to temperature mediates herbivory

Species interactions drive ecosystem processes and are a major focus of global change research. Among the most consequential interactions expected to shift with climate change are those between insect herbivores and plants, both of which are highly sensitive to temperature. Insect herbivores and their host plants display varying levels of synchrony that could be disrupted or enhanced by climate change, yet empirical data on changes in synchrony are lacking. Using evidence of herbivory on herbarium specimens collected from the northeastern United States and France from 1900 to 2015, we provide evidence that plant species with temperature-sensitive phenologies experience higher levels of insect damage in warmer years, while less temperature-sensitive, co-occurring species do not. While herbivory might be mediated by interactions between warming and phenology through multiple pathways, we suggest that warming might lengthen growing seasons for phenologically sensitive plant species, exposing their leaves to herbivores for longer periods of time in warm years. We propose that elevated herbivory in warm years may represent a previously underappreciated cost to phenological tracking of climate change over longer timescales.

Spatiotemporal Dynamics of 20th-Century Spruce Budworm Outbreaks in Eastern Canada: Three Distinct Patterns of Outbreak Severity

Spruce budworm (SBW) outbreaks are a major disturbance in North American forests. In Quebec, Canada, the recent history of SBW outbreaks at the local scale is well-known. Studies at the Québec scale nonetheless remain rare despite the need to better understand the dynamics of SBW outbreaks at a larger scale. This study aimed to reconstruct the spatiotemporal dynamics of SBW outbreaks during the 20th century across the insect's range in southern Quebec. To this end, we sampled 83 stands throughout southern Quebec. These stands were selected according to their age and the presence of black, white, and red spruce. In fact, spruce, unlike balsam fir, survives the SBW outbreaks and can record them in these growth rings. In each stand, cores were taken from 20 spruce trees. The dendrochronological series of more than 1,600 trees were analyzed, and we identified, through the k-means grouping of stands, the spatial patterns of tree growth for the three previously documented 20th century SBW outbreaks. The outbreaks were not homogeneous across the distribution range of the insect. Two groups of stands showed early- (1905–1930) and late-century (1968–1988) outbreaks of high severity and a mid-century (1935–1965) outbreak of moderate severity. This pattern is explained mainly by the presence of the insect within the balsam fir–yellow birch and balsam fir–white birch bioclimatic domains, areas where outbreaks tend to be most severe because of the abundance of balsam fir, the main SBW host species. However, these two models differ in terms of the duration of outbreaks. A third, more northern, cluster of stands experienced lower severity outbreaks over the 20th century, a pattern explained by a lower proportion of balsam fir trees in these landscapes. Our study shows that, on the one hand, these three groups of stands are defined by outbreaks of specific duration (an outbreak period beginning when more than 20% of the trees are affected and ending when <20% of the trees are affected) and severity (in terms of percentage of affected trees), and on the other hand they are spatially distinct and subject to different climatic conditions.

Detecting Tree Species Effects on Forest Canopy Temperatures with Thermal Remote Sensing: The Role of Spatial Resolution

Canopy temperatures are important for understanding tree physiology, ecology, and their cooling potential, which provides a valuable ecosystem service, especially in urban environments. Linkages between tree species composition in forest stands and air temperatures remain challenging to quantify, as the establishment and maintenance of onsite sensor networks is time-consuming and costly. Remotely-sensed land surface temperature (LST) observations can potentially acquire spatially distributed crown temperature data more efficiently. We analyzed how tree species modify canopy air temperature at an urban floodplain forest (Leipzig, Germany) site equipped with a detailed onsite sensor network, and explored whether mono-temporal thermal remote sensing observations (August, 2016) at different spatial scales could be used to model air temperatures at the tree crown level. Based on the sensor-network data, we found interspecific differences in summer air temperature to vary temporally and spatially, with mean differences between coldest and warmest tree species of 1 °C, and reaching maxima of up to 4 °C for the upper and lower canopy region. The detectability of species-specific differences in canopy surface temperature was found to be similarly feasible when comparing high-resolution airborne LST data to the airborne LST data aggregated to 30 m pixel size. To realize a spatial resolution of 30 m with regularly acquired data, we found the downscaling of Landsat 8 thermal data to be a valid alternative to airborne data, although detected between-species differences in surface temperature were less expressed. For the modeling of canopy air temperatures, all LST data up to the 30 m level were similarly appropriate. We thus conclude that satellite-derived LST products could be recommended for operational use to detect and monitor tree species effects on temperature regulation at the crown scale.

Linking radial growth patterns and moderate-severity disturbance dynamics in boreal old-growth forests driven by recurrent insect outbreaks: A tale of opportunities, successes, and failures

In boreal landscapes, emphasis is currently placed on close-to-nature management strategies, which aim to maintain the biodiversity and ecosystem services related to old-growth forests. The success of these strategies, however, depends on an accurate understanding of the dynamics within these forests. While moderate-severity disturbances have recently been recognized as important drivers of boreal forests, little is known about their effects on stand structure and growth. This study therefore aimed to reconstruct the disturbance and postdisturbance dynamics in boreal old-growth forests that are driven by recurrent moderate-severity disturbances. We studied eight primary old-growth forests in Québec, Canada, that have recorded recurrent and moderately severe spruce budworm (Choristoneura fumiferana [Clem.]) outbreaks over the 20th century. We applied an innovative dendrochronological approach based on the combined study of growth patterns and releases to reconstruct stand disturbance and postdisturbance dynamics. We identified nine growth patterns; they represented trees differing in age, size, and canopy layer. These patterns highlighted the ability of suppressed trees to rapidly fill gaps created by moderate-severity disturbances through a single and significant increase in radial growth and height. Trees that are unable to attain the canopy following the disturbance tend to remain in the lower canopy layers, even if subsequent disturbances create new gaps. This combination of a low stand height typical of boreal forests, periodic disturbances, and rapid canopy closure often resulted in stands constituted mainly of dominant and codominant trees, similar to even-aged forests. Overall, this study underscored the resistance of boreal old-growth forests owing to their capacity to withstand repeated moderate-severity disturbances. Moreover, the combined study of growth patterns and growth release demonstrated the efficacy of such an approach for improving the understanding of the fine-scale dynamics of natural forests. The results of this research will thus help develop silvicultural practices that approximate the moderate-severity disturbance dynamics observed in primary and old-growth boreal forests.

Driving factors of conifer regeneration dynamics in eastern Canadian boreal old-growth forests

Old-growth forests play a major role in conserving biodiversity, protecting water resources, and sequestrating carbon, as well as serving as indispensable resources for indigenous societies. Novel silvicultural practices must be developed to emulate the natural dynamics and structural attributes of old-growth forests and preserve the ecosystem services provided by these boreal ecosystems. The success of these forest management strategies depends on developing an accurate understanding of natural regeneration dynamics. Our goal was therefore to identify the main patterns and drivers involved in the regeneration dynamics of old-growth forests with a focus on boreal stands dominated by black spruce (Picea mariana (L.) Mill.) and balsam fir (Abies balsamea (L.) Mill.) in eastern Canada. We sampled 71 stands in a 2 200 km2 study area located within Quebec's boreal region. For each stand, we noted tree regeneration (seedlings and saplings), structural attributes (diameter distribution, deadwood volume, etc.), and abiotic (slope and soil) factors. The presence of seed-trees located nearby and slopes having moderate to high angles most influenced balsam fir regeneration. In contrast, the indirect indices of recent secondary disturbances (e.g., insect outbreaks or windthrows) and topographic constraints (slope and drainage) most influenced black spruce regeneration. We propose that black spruce regeneration dynamics can be separated into distinct phases: (i) layering within the understory, (ii) seedling growth when gaps open in the canopy, (iii) gradual canopy closure, and (iv) production of new layers once the canopy is closed. These dynamics are not observed in paludified stands or stands where balsam fir is more competitive than black spruce. Overall, this research helps explain the complexity of old-growth forest dynamics, where many ecological factors interact at multiple temporal and spatial scales. This study also improves our understanding of ecological processes within primary old-growth forests and identifies the key factors to consider when ensuring the sustainable management of old-growth boreal stands.

Host Tree Species Affects Spruce Budworm Winter Survival

With current trends in global warming, it has been suggested that spruce budworm outbreaks may spread to northern parts of the boreal forest. However, the major constraints for a northward expansion are the availability of suitable host trees and the insect winter survival capacity. This study aimed to determine the effect of larval feeding on balsam fir, white spruce and black spruce on various spruce budworm life history traits of both the parental and the progeny generations. Results indicated that the weight of the overwintering larval progeny and their winter survival were influenced by host tree species on which larvae of the parental generation fed. White spruce was the most suitable host for the spruce budworm, producing the heaviest pupae and the heaviest overwintering larvae while black spruce was the least suitable, producing the smallest pupae and the smallest overwintering progeny. Overwintering larvae produced by parents that fed on black spruce also suffered higher winter mortality than individuals coming from parents that fed on balsam fir or white spruce. With current trends in global warming, spruce budworm is expected to expand its range to northern boreal forests where black spruce is the dominant tree species. Such northern range expansion might not result in outbreaks if low offspring winter survival on black spruce persist.

Warming counteracts defoliation-induced mismatch by increasing herbivore-plant phenological synchrony

Climate change is altering phenology; however, the magnitude of this change varies among taxa. Compared with phenological mismatch between plants and herbivores, synchronization due to climate has been less explored, despite its potential implications for trophic interactions. The earlier budburst induced by defoliation is a phenological strategy for plants against herbivores. Here, we tested whether warming can counteract defoliation-induced mismatch by increasing herbivore-plant phenological synchrony. We compared the larval phenology of spruce budworm and budburst in balsam fir, black spruce, and white spruce saplings subjected to defoliation in a controlled environment at temperatures of 12, 17, and 22°C. Budburst in defoliated saplings occurred 6-24 days earlier than in the controls, thus mismatching needle development from larval feeding. This mismatch decreased to only 3-7 days, however, when temperatures warmed by 5 and 10°C, leading to a resynchronization of the host with spruce budworm larvae. The increasing synchrony under warming counteracts the defoliation-induced mismatch, disrupting trophic interactions and energy flow between forest ecosystem and insect populations. Our results suggest that the predicted warming may improve food quality and provide better growth conditions for larval development, thus promoting longer or more intense insect outbreaks in the future.

Prediction of the Long-Term Potential Distribution of Cryptorhynchus lapathi (L.) under Climate Change

The poplar and willow borer, Cryptorhynchus lapathi (L.), is a severe worldwide quarantine pest that causes great economic, social, and ecological damage in Europe, North America, and Asia. CLIMEX4.0.0 was used to study the likely impact of climate change on the potential global distribution of C. lapathi based on existing (1987–2016) and predicted (2021–2040, 2041–2080, and 2081–2100) climate data. Future climate data were simulated based on global climate models from Coupled Model Inter-comparison Project Phase 5 (CMIP5) under the RCP4.5 projection. The potential distribution of C. lapathi under historical climate conditions mainly includes North America, Africa, Europe, and Asia. Future global warming may cause a northward shift in the northern boundary of potential distribution. The total suitable area would increase by 2080–2100. Additionally, climatic suitability would change in large regions of the northern hemisphere and decrease in a small region of the southern hemisphere. The projected potential distribution will help determine the impacts of climate change and identify areas at risk of pest invasion in the future. In turn, this will help design and implement effective prevention measures for expanding pest populations, using natural enemies, microorganisms, and physical barriers in very favorable regions to impede the movement and oviposition of C. lapathi.

Modelling Post-Disturbance Successional Dynamics of the Canadian Boreal Mixedwoods

Natural disturbances, such as fire and insect outbreaks, play important roles in natural forest dynamics, which are characterized over long time scales by changes in stand composition and structure. Individual-based forest simulators could help explain and predict the response of forest ecosystems to different disturbances, silvicultural treatments, or environmental stressors. This study evaluated the ability of the SORTIE-ND simulator to reproduce post-disturbance dynamics of the boreal mixedwoods of eastern Canada. In 1991 and 2009, we sampled all trees (including seedlings and saplings) in 431 (256 m2) plots located in the Lake Duparquet Research and Teaching Forest (western Quebec). These plots were distributed in stands originating from seven wildfires that occurred between 1760 and 1944, and which represented a chronosequence of post-disturbance stand development. We used the 1991 inventory data to parameterize the model, and simulated short- to long-term natural dynamics of post-fire stands in both the absence and presence of a spruce budworm outbreak. We compared short-term simulated stand composition and structure with those observed in 2009 using a chronosequence approach. The model successfully generated the composition and structure of empirical observations. In long-term simulations, species dominance of old-growth forests was not accurately estimated, due to possible differences in stand compositions following wildfires and to differences in stand disturbance histories. Mid- to long-term simulations showed that the secondary disturbance incurred by spruce budworm did not cause substantial changes in early successional stages while setting back the successional dynamics of middle-aged stands and accelerating the dominance of white cedar in late-successional post-fire stands. We conclude that constructing a model with appropriate information regarding stand composition and disturbance history considerably increases the strength and accuracy of the model to reproduce the natural dynamics of post-disturbance boreal mixedwoods.

A Conceptual Framework for the Spruce Budworm Early Intervention Strategy: Can Outbreaks be Stopped?

The spruce budworm, Choristoneura fumiferana, Clem., is the most significant defoliating pest of boreal balsam fir (Abies balsamea (L.) Mill.) and spruce (Picea sp.) in North America. Historically, spruce budworm outbreaks have been managed via a reactive, foliage protection approach focused on keeping trees alive rather than stopping the outbreak. However, recent theoretical and technical advances have renewed interest in proactive population control to reduce outbreak spread and magnitude, i.e., the Early Intervention Strategy (EIS). In essence, EIS is an area-wide management program premised on detecting and controlling rising spruce budworm populations (hotspots) along the leading edge of an outbreak. In this article, we lay out the conceptual framework for EIS, including all of the core components needed for such a program to be viable. We outline the competing hypotheses of spruce budworm population dynamics and discuss their implications for how we manage outbreaks. We also discuss the practical needs for such a program to be successful (e.g., hotspot monitoring, population control, and cost–benefit analyses), as well as the importance of proactive communications with stakeholders.

Prey-predator phenological mismatch under climate change

Insect phenology is affected by climate change and main responses are driven by phenotypic plasticity and evolutionary changes. Any modification in seasonal activity in one species can have consequences on interacting species, within and among trophic levels. In this overview, we focus on synchronisation mismatches that can occur between tightly interacting species such as hosts and parasitoids or preys and predators. Asynchronies happen because species from different trophic levels can have different response rates to climate change. We show that insect species alter their seasonal activities by modifying their life-cycle through change in voltinism or by altering their development rate. We expect strong bottom-up effects for phenology adjustments rather than top-down effects within food-webs. Extremely complex outcomes arise from such trophic mismatches, which make consequences at the community or ecosystem levels tricky to predict in a climate change context. We explore a set of potential consequences on population dynamics, conservation of species interactions, with a particular focus on the provision of ecosystem services by predators and parasitoids, such as biological pest control.