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Summary 1.Range expansions mediated by recent climate warming have been documented for many insect species, including some important forest pests. However, whether climate change also influences the eruptive dynamics of forest pest insects, and hence the ecological and economical consequences of outbreaks, is largely unresolved. 2. Using historical outbreak records covering more than a century, we document recent outbreak range expansions of two species of cyclic geometrid moth, Operophtera brumata Bkh. (winter moth) and Epirrita autumnata L. (autumnal moth), in subarctic birch forest of northern Fennoscandia. The two species differ with respect to cold tolerance, and show strikingly different patterns in their recent outbreak range expansion. 3. We show that, during the past 15-20 years, the less cold-tolerant species O. brumata has experienced a pronounced north-eastern expansion into areas previously dominated by E. autumnata outbreaks . Epirrita autumnata , on the other hand, has expanded the region in which it exhibits regular outbreaks into the coldest, most continental areas. Our findings support the suggestion that recent climate warming in the region is the most parsimonious explanation for the observed patterns. 4. The presence of O. brumata outbreaks in regions previously affected solely by E. autumnata outbreaks is likely to increase the effective duration of local outbreaks, and hence have profound implications for the subarctic birch forest ecosystem.

Although it is well known that insects are sensitive to temperature, how they will be affected by ongoing global warming remains uncertain because these responses are multifaceted and ecologically complex. We reviewed the effects of climate warming on 31 globally important phytophagous (plant‐eating) insect pests to determine whether general trends in their responses to warming were detectable. We included four response categories (range expansion, life history, population dynamics, and trophic interactions) in this assessment. For the majority of these species, we identified at least one response to warming that affects the severity of the threat they pose as pests. Among these insect species, 41% showed responses expected to lead to increased pest damage, whereas only 4% exhibited responses consistent with reduced effects; notably, most of these species (55%) demonstrated mixed responses. This means that the severity of a given insect pest may both increase and decrease with ongoing climate warming. Overall, our analysis indicated that anticipating the effects of climate warming on phytophagous insect pests is far from straightforward. Rather, efforts to mitigate the undesirable effects of warming on insect pests must include a better understanding of how individual species will respond, and the complex ecological mechanisms underlying their responses.

Summary1. Home range size, spatial organization and territoriality of reproductive Arctic foxes were studied during the summer. The influence of spatial distribution and availability of the main prey was investigated in order to evaluate whether the spatial organization of Arctic foxes was coherent with key predictions of the resource dispersion hypotheses (RDH). The RDH includes the spatial characteristics of resource abundance, while there is also growing attention to the importance of the temporal characteristics of resource abundance. Hence the role of temporal and spatio-temporal predictability of prey explaining carnivore spatial organization was also investigated in this study. 2. The study was conducted on Svalbard; a simple High-Arctic terrestrial ecosystem which allowed unique estimates of prey abundance. The main prey of the Arctic fox (Svalbard reindeer Rangifer tarandus platyrhynchus , seabirds Alcidae and Procellariidae and geese Anseridae ) was surveyed systematically. These surveys revealed highly contrasting patterns in prey abundance within the terrestrial ecosystem. 3. Arctic fox summer home ranges varied in size (4-60 km 2 ), as well as in overlap (17-76%). The diverse spatial organization covaried with spatial and temporal patterns in prey abundance. Small home ranges (10 ± 5·6 km 2 ) with large overlap (76 ± 19·6%) were characteristic for coastal areas where prey was concentrated in small patches and predictable both in space and time. Medium home ranges (23 ± 4·2 km 2 ) and overlap (50 ± 6·6%) occurred inland where prey was clumped in larger patches and less predictable. Large home ranges (52 ± 8·4 km 2 ) with little overlap (17 ± 3·5%) occurred inland where prey was widely scattered and unpredictable. 4. Spatial dispersion and richness of prey resources explained most of the variation in Arctic fox spatial organization. The RDH framework could be used to explain the presence of relaxed territoriality found in this study. We suggest that the observed absence of more permanent social groups is due to the extremely severe winter conditions which force juvenile individuals to disperse from the natal area during the first winter. 5. Predictability of resources was an additional significant factor affecting both home-range size and overlap. Resource predictability captures the degree to which an animal can depend on its environment to offer suitable and secure living conditions over time. 6. This study emphasize the need to incorporate both spatial and temporal characteristics of resource distribution in order to fully understand the diversity of spatial arrangements among carnivores.

The release of cold temperature constraints on photosynthesis has led to increased productivity (greening) in significant parts (32-39%) of the Arctic, but much of the Arctic shows stable (57-64%) or reduced productivity (browning, <4%). Summer drought and wildfires are the bestdocumented drivers causing browning of continental areas, but factors dampening the greening effect of more maritime regions have remained elusive. Here we show how multiple anomalous weather events severely affected the terrestrial productivity during one water year (October 2011-September 2012) in a maritime region north of the Arctic Circle, the Nordic Arctic Region, and contributed to the lowest mean vegetation greenness (normalized difference vegetation index) recorded this century. Procedures for field data sampling were designed during or shortly after the events in order to assess both the variability in effects and the maximum effects of the stressors. Outbreaks of insect and fungal pests also contributed to low greenness. Vegetation greenness in 2012 was 6.8% lower than the 2000-11 average and 58% lower in the worst affected areas that were under multiple stressors. These results indicate the importance of events (some being mostly neglected in climate change effect studies and monitoring) for primary productivity in a high-latitude maritime region, and highlight the importance of monitoring plant damage in the field and including frequencies of stress events in models of carbon economy and ecosystem change in the Arctic. Fourteen weather events and anomalies and 32 hypothesized impacts on plant productivity are summarized as an aid for directing future research.