Abstract
Global change challenges the adaptive potential of forests. Large-scale alterations of forest canopies have been reported across Europe, and further modifications are expected in response to the predicted changes in drought and windstorm regimes. Since forest canopies are dynamic interfaces between atmosphere and land surface, communities of canopy-dwelling insects are at the forefront of major changes in response to both direct and indirect effects of climate change. First, we briefly introduce the factors shaping arthropod communities in the canopy of temperate forests. Second, we cover the significant impacts of a forest decline on canopy structure and functioning, and more specifically its contrasted effects on insect microhabitats, trophic resources and forest microclimates. Deleterious effects may be expected for several guilds of leaf-dwelling insects. Nonetheless, a forest decline could also lead to transient or long-lasting resource pulses for other canopy-dwelling guilds, especially saproxylic species depending on deadwood substrates and tree-related microhabitats. The novel microclimates may also become more favorable for some particular groups of insects. We pinpoint current knowledge gaps and the technological locks that should be undone to improve our understanding of the canopy biotope and biodiversity in temperate forests. We highlight the need for integrative approaches to reveal the mechanisms at play. We call for cross-scale studies and long-term collaborative research efforts, involving different disciplines such as community and disturbance ecology, plant and insect ecophysiology, and thermal ecology, to better anticipate ongoing functional and conservation issues in temperate forest ecosystems.
Highlights
Forest ecosystems worldwide are currently facing increasing levels of environmental stress, posing severe challenges to their adaptive capacity (Allen et al, 2010; Seidl et al, 2017)
Drought and windstorms have been identified as major drivers of recent forest diebacks and declines in temperate Europe, either through their direct impacts on tree health and survival or by promoting large-scale outbreaks of opportunistic species (Carnicer et al, 2011; Sallé et al, 2014; Seidl et al, 2014, 2017; Biedermann et al, 2019; Senf et al, 2020)
Biodiversity in the Canopy of Declining Forests have been increasing in Europe during the last decades, with a recent acceleration (Gregow et al, 2017; Senf et al, 2020)
Summary
Forest ecosystems worldwide are currently facing increasing levels of environmental stress, posing severe challenges to their adaptive capacity (Allen et al, 2010; Seidl et al, 2017). Drought and windstorms have been identified as major drivers of recent forest diebacks and declines in temperate Europe, either through their direct impacts on tree health and survival or by promoting large-scale outbreaks of opportunistic species (Carnicer et al, 2011; Sallé et al, 2014; Seidl et al, 2014, 2017; Biedermann et al, 2019; Senf et al, 2020). Droughts and windstorms can directly affect canopy structure by inducing leaf and twig shedding, and provoking branch and stem breakage (Bréda et al, 2006; Mitchell, 2013) They can have long-lasting effects when they act as inciting factors of forest declines (Manion, 1981). Our aim is to highlight the gaps in our knowledge on the functional response of temperate forest ecosystems to global environmental change, and to stimulate cross-scale studies involving various disciplines to ameliorate predictions that should feed management plans
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