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Climate change impacts on species and ecosystem functioning may depend on climatic context and study systems. Climate warming and intensified herbivory are two stressors to plants that often appear in combination and are predicted to increase in cold environments. Effects of multiple drivers on plant performance are difficult to predict and warrant studies that use experimental manipulations along climatic gradients to produce more realistic knowledge. Our three study sites by the Sognefjord in Norway, that differed mainly in climatic conditions (ca. 5°C growing season difference), ranged from hemi-boreal lowland (100 masl, Low), via boreal mid-montane (500 masl) to alpine timberline (900 masl, High) bioclimates. At each site, in a randomized block design, we simulated growing-season warming using open-top chambers (OTCs) and experimentally induced herbivory resistance using the plant hormone methyl jasmonate (MeJA). We recorded growth, mortality, flower and fruit numbers, and insect herbivory on tagged ramets in permanent plots across three years (2016-2018) in three open woodland populations of two functionally important plant species with contrasting traits, Vaccinium myrtillus (bilberry) and V. vitis-idaea (lingonberry). Growth of both dwarf shrubs decreased with warming in the warm lowland populations (Low) but increased in the alpine populations (High). Shoot mortality increased most with warming at Low but was reduced at High. Reproduction, both flowering and fruiting, decreased with induced resistance treatment, but the effect was larger when warmed for bilberry and increased with elevation for both species. Leaf herbivory in bilberry increased with warming at Low but decreased at High. The combined warming and resistance treatment had only synergistic negative interaction effects on fruit numbers in bilberry. The clear context-and species-dependent effects of climate warming and increased resistance in this study may predict a potential decline in performance, as well as abundance and distribution, of these functionally important Vaccinium species at our lowest site. Bilberry reproduction appeared to be particularly susceptible to both climate warming and induced resistance in the manipulated populations. Such combined negative effects on plant performance are likely to have considerable knock-on effects via altered species' interactions and ecosystem functioning. [ABSTRACT FROM AUTHOR]

Globally, climate change greatly impacts the production of major crops, and there have been many attempts to model future yields under warming scenarios in recent years. However, projections of future yields may not be generalisable to all crop growing regions, particularly those with diverse topography and bioclimates. In this study, we demonstrate this by evaluating the links between changes in temperature and precipitation and changes in wheat, barley, and potato yields at the county-level during 1980–2019 in Norway, a Nordic country with a range of climates across a relatively small spatial scale. The results show that the impacts of climate variables on yield vary widely by county, and that for some crops, the strength and direction of the link depends on underlying local bioclimate. In addition, our analysis demonstrates the need for some counties to focus on weather changes during specific crucial months corresponding with certain crop growth stages. Furthermore, due to the local climatic conditions and varying projected climate changes, different production opportunities are likely to occur in each county. [ABSTRACT FROM AUTHOR]

Glacier forelands provide important sites to study climate-forced ecological succession because a chronosequence is apparent along a single valley. However, most studies of invertebrate succession in forelands provide a single snapshot of community assemblage patterns. With glaciers retreating rapidly worldwide, it is important to begin re-surveying community composition and assessing changes in relation to new terrain revealed by the retreating ice. In this study, we repeat a survey of spiders and beetles along the glacier foreland of the sub-alpine glacier Austerdalsbreen in western Norway, 15 years after an initial assessment in 2004, during which time the glacier has retreated 400 m. Invertebrates were sampled in 18 sites that represent a terrain age gradient of approximately 10–250 years since glacier recession. Forty spider species and 70 beetle species were identified, constituting the richest record in Nordic glacier forelands for these two taxonomic groups. Furthermore, three distinctive stages of succession were determined using TWINSPAN and NMDS: (1) a pioneer colonizer stage; (2) an intermediate successional stage; and (3) two late colonizer stages. Additionally, a species group of omnipresent species was identified. The transition from pioneer stage to early succession was characterized by a high degree of taxonomic replacement. Compared to the findings in 2004, we found that the composition of species groups on relatively old terrain is becoming more similar, while the differences between the species groups on the younger terrain are widening. This discrepancy is discussed in relation to climate warming, which potentially facilitates faster establishment of vegetation and early successional invertebrates and may therefore increase competition stress for cold-adapted pioneer species. [ABSTRACT FROM AUTHOR]

Plants have the capacity to alter their phenotype in response to environmental factors, such as herbivory, a phenomenon called phenotypic plasticity. However, little is known on how plant responses to herbivory are modulated by environmental variation along ecological gradients. To investigate this question, we used bilberry (Vaccinium myrtillus L.) plants and an experimental treatment to induce plant defenses (i.e., application of methyl jasmonate; MeJA), to observe ecological responses and gene expression changes along an elevational gradient in a boreal system in western Norway. The gradient included optimal growing conditions for bilberry in this region (ca. 500 m a.s.l.), and the plant's range limits at high (ca. 900 m a.s.l.) and low (100 m a.s.l.) elevations. Across all altitudinal sites, MeJA‐treated plants allocated more resources to herbivory resistance while reducing growth and reproduction than control plants, but this response was more pronounced at the lowest elevation. High‐elevation plants growing under less herbivory pressure but more resource‐limiting conditions exhibited consistently high expression levels of defense genes in both MeJA‐treated and untreated plants at all times, suggesting a constant state of "alert." These results suggest that plant defense responses at both the molecular and ecological levels are modulated by the combination of climate and herbivory pressure, such that plants under different environmental conditions differentially direct the resources available to specific antiherbivore strategies. Our findings are important for understanding the complex impact of future climate changes on plant–herbivore interactions, as this is a major driver of ecosystem functioning and biodiversity. [ABSTRACT FROM AUTHOR]

• Abundance of rowan saplings increased excessively in old growth boreal forest when excluding ungulates or when herbivore density decreased. • Rowan growth was clearly limited by ungulate browsing, and saplings were not able to escape the "browse trap" by growing beyond ca. half a meter. • Rowan saplings established in juniper nurse plants were protected against browsing and showed reduced mortality and increased growth. • Our study showed that nurse plants enabled saplings to escape from feeding ungulates in boreal forest. Recent increases in ungulate herbivore populations have intensified browsing pressure in northern forest ecosystems. High browsing pressure affects recruitment into tree populations and saplings are among the most impacted and critical tree stages. This calls for research on factors that enhance sapling survival and promote recovery of herbivore preferred species. One understudied factor in ungulate dominated boreal forests is the ability of young trees to escape large herbivores by utilising "nurse plants". First, we examined the impact of ungulate browsing on the abundance and size of rowan (Sorbus aucuparia), a functionally important tree species in an old-growth boreal pine forest, western Norway. The responses were compared between exclosures and ungulate-access plots over ten years (2001–2011) combined with investigations along a browsing intensity gradient (Exp. A). In a second experiment we investigated whether rowan saplings escape browsing and enhance growth and survival by growing within nurse plants. Consequently, we planted rowan saplings in ungulate browsing areas, inside and outside coniferous juniper (Juniper communis) bushes, and analysed the treatment effect on browsing, growth, and survival of rowan saplings across five years (2013–2018; Exp B). Excluding large herbivores resulted in a large increase in rowan saplings which were six times more abundant in exclosures (0.44 ind./m2) compared to ungulate-access plots (0.07 ind./m2) after ten years (Exp. A). The abundance of rowan saplings also decreased with higher browsing intensity. Moreover, the rowans in exclosures grew to almost twice the height of the ungulate-access rowans. The protected rowan saplings experienced significantly less browsing damage, and only 25% of the protected plants experienced heavy browsing or died after the first winter, compared to 70% of the unprotected plants (Exp. B). After five years, 50% more unprotected than protected plants experienced heavy browsing or mortality, and growth in protected plants was nearly 50% greater over the period. The negative impact of ungulate browsing on abundance and growth of rowans can be counteracted by positive plant-plant interactions. Rowan saplings growing within nurse plants showed significantly less browsing and better performance indicating high functional importance of the forest understorey. Forest managed with multi-layered and multi-species understoreys may therefore also be beneficial for tree recruitment in browsed boreal forest landscapes. [ABSTRACT FROM AUTHOR]

This article examines the abundance, life history, host-plant relationships, and overwintering biology of Acyrthosiphon calvulus Ossiannilsson (Homoptera: Aphididae) as a precursor to understanding its rarity and potential response to a changing climate. Acyrthosiphon calvulus is restricted to a few scattered localities on the west coast of Spitsbergen, Svalbard, Norway, where it reproduces on Salix polaris WG (Salicaceae) and its taxonomically unrelated root parasite Pedicularis hirsuta L. (Scrophulariaceae) . Acyrthosiphon calvulus overwinters as eggs. Hatching fundatrices give rise directly to males and oviparae, which mate and lay overwintering eggs. The life cycle is closely synchronized with the phenology of S. polaris and appears genetically programmed, lacking summer generations of viviparae. Alate forms are similarly unknown. The progeny sequence of fundatrices resulted in a sex ratio for the sexuales that is strongly female biased (3:1). Eggs hatch coincided with budburst in early June and fundatrices developed on the expanding leaves. Egg production by oviparae corresponded with leaf senescence in July and August. Overwintering egg survival was high, with supercooling points ranging from −29 to −40 °C, lower than the extreme winter minimum temperature recorded (−28 °C). Egg development and hatching occurred at or below 5 °C and sub-zero temperatures were not required to break diapause. The scarcity and fragmented distribution of A. calvulus is discussed in the context of the ubiquity of its host plants on Spitsbergen. [ABSTRACT FROM AUTHOR]