Forest Insects and Climate Change

Current Forestry Reports (2018) 4:35–50 https://doi.org/10.1007/s40725-018-0075-6 FOREST ENTOMOLOGY (E BROCKERHOFF, SECTION EDITOR) Forest Insects and Climate Change Deepa S. Pureswaran 1 & Alain Roques 2 & Andrea Battisti 3 Published online: 30 April 2018 # The Author(s) 2018 Abstract Purpose of Review Climate change affects populations of forest insect pests in a number of ways. We reviewed the most recent literature (2013–2017) on this subject including previous reviews on the topic. We provide a comprehensive discussion of the subject, with special attention to insect range expansion, insect abundance, impacts on forest ecosystems, and effects on forest insect communities. We considered forest insects according to their major guilds and biomes. Recent Findings Effects of climate change on forest insects are demonstrated for a number of species and guilds, although generalizations of results available so far are difficult because of species-specific responses to climate change. In addition, disentangling direct and indirect effects of climate change is complex due to the large number of variables affected. Modeling based on climate projections is useful when combined with mechanistic explanations. Summary Expansion of either the true range or the outbreak range is observed in several model species/groups of major insect guilds in boreal and temperate biomes. Mechanistic explanations are provided for a few species and are mainly based on increase in winter temperatures. In relation to insect abundance, climate change can either promote outbreaks or disrupt trophic interactions and decrease the severity of outbreaks. There is good evidence that some recent outbreaks of bark beetles and defoliating insects are influenced by climate change and are having a large impact on ecosystems as well as on communities of forest insects. Keywords Biome . Community . Guild . Impact . Outbreak . Range . Review Introduction There is general consensus among scientists that the global climate is changing at an unprecedented rate, with many regions experiencing warming trends, frequent high temperature extremes, and shifts in precipitation patterns [1••]. An increase of 0.61 °C in global mean temperature recorded since the beginning of the twentieth century (i.e., comparing the years 1850–1900 and 1986–2005, 5–95% CI is This article is part of the Topical Collection on Forest Entomology * Deepa S. Pureswaran 1 Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, 1055, rue du PEPS, Québec, QC G1V 4C7, Canada 2 Institut National de la Recherche Agronomique (INRA), UR 0633, Zoologie Forestière, 45075 Orléans, France 3 Department of Agronomy, Food, Natural resources Animals and Environment (DAFNAE), University of Padova, 35020 Legnaro, Italy 0.55–0.67 °C) [1, 2], and the predicted warming of 2–6 °C by 2100 [3] have direly increased the need to understand the impacts of climate change. Interactions and feedbacks between climate and the health of forest ecosystems are expected [4]. Changes in disturbance patterns mediated by climate warming are predicted to be the greatest impacts on forests in the coming decades [5]. Current increases in frequency and intensity of biotic and abiotic disturbances to forest ecosystems have been attributed, at least in part, to climate change [1••], but uncertainties remain in a number of cases. Outbreaks of forest insects are major agents of mortality and ecosystem change in forests worldwide, and climate has been attributed to be an important driver of changes to disturbance regimes mediated by forest insects. Largescale tree mortality resulting from drought, fire, and/or insect outbreaks can result in loss of carbon sinks and have feedbacks on climate change, with serious consequences for biodiversity and ecosystem function [6•, 7]. Disturbances have been defined as Bdisrupting the function of an ecosystem and changing resource availability or the physical environment^ [5]. Consequences of disturbance can result in loss of resilience accompanied by major ecological 36 transformations [8]. Forest insect outbreaks are major disturbances by native or non-native insects, as they can be synchronous over large geographic areas and cause region-wide mortality of host trees in a relatively short period of time [9, 10, 11•, 12]. Disturbance due to forest insects have been recorded to increase land surface temperature and cause declines in gross primary productivity [13, 14]. Predicted geophysical impacts of climate change include floods, droughts, and rise in sea levels. General circulation models predict the greatest warming at high latitudes in winter, a decrease in precipitation at mid-latitudes in summer, and an increase in frequency of extreme climatic events such as storms and droughts [4]. Bark beetles, for example, can cause tree mortality following severe drought that is associated with warm temperatures, due to positive feedbacks on their populations from availability of susceptible hosts and favorable temperatures, amplified over spatial and temporal scales [10, 15•]. Predictions of insect outbreaks suggest changes in spatiotemporal patterns of defoliators and bark beetles. Bentz et al. [16] predict that spruce bark beetle, Dendroctonus rufipennis, outbreaks may occur throughout the range of spruce in North America in the future. Outbreak dynamics of the spruce budworm, Choristoneura fumiferana, are predicted to change, move further north, and on to secondary host species [17, 18]. Similarly, cyclical outbreaks of larch bud moth, Zeiraphera griseana, are predicted to decrease in magnitude in optimal mid-elevation zones of the Alps, and to shift toward higher altitudes [19]. However, predictions on future outbreak dynamics of defoliators remain uncertain as there is conflicting evidence on outbreak severity [20]. In general, poleward and upward shifts of pests and pathogens have been documented, but predictions are complicated due to interactions and uncertainties associated with changing weather patterns, extreme climate events, and differing responses of plants and insects to these events [21]. The consequences of higher frequency of extreme events are still poorly documented. For example, both positive and negative effects of climate on expansion and population dynamics can occur, as was observed in the pine processionary moth, Thaumetopoea pityocampa, during summer heat waves in 2003. This heat wave led to a collapse of the front edge population in France by killing early stages of the insect [22], while at the same time, triggering a record annual expansion in the Italian Alps by facilitating female flight [23]. Insect populations are particularly responsive to climate change because of their sensitivity to temperature, short generation times, and high flight capacity. Observations of insect herbivory on an oak lineage during Quaternary climate change indicate that there was higher damage during warm and wet per (...truncated)