Data availabilityThe datasets generated during and/or analyzed during the current study are not publicly available due to further analyses on the data but are available from the corresponding author on reasonable request. Declaration on conflicts of interestThe authors declare that they have no conflict of interest. Total number of characters: 66 681 Number of tables: 5 (+1 in supplementary data) Number of figures: 6 (+ 1 in supplementary data) Reference to pre-print servers (when relevant):The Preprint version of this article is available in the BioRxiv server, https://www.biorxiv.org/content/10.1101/2020.02.11.943753v1 . CC-BY 4.0 International license available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made Forest decline differentially affects trophic guilds of canopy-dwelling beetles Key messageDecline can affect the structure, resources and microclimates of the forest canopy, and potentially have cascading effects on canopy-dwelling species. Our survey shows that an oak decline can promote saproxylic beetles, especially xylophagous ones, and generalist phyllophagous weevils. However, it negatively affects specialist phyllophagous species and has no effect on seminiphagous weevils.

The ongoing global change could be an additional threat to the establishment and the long-term survival of Populus nigra L., an emblematic European riparian species. With the general aim of gaining insights into the adaptive potential of this species, we (i) quantified variations within and among three French P. nigra populations for key physiological attributes, i.e., water-use efficiency (assessed from bulk leaf carbon isotope discrimination, Δ(13)C), growth performance and related leaf traits, (ii) examined genotype and population by environment interactions, and (iii) explored the relationship between Δ(13)C and growth. Thirty genotypes were sampled in each of three naturally established populations and grown in two different sites, Orléans (ORL) and Guémené-Penfao (GMN). In ORL, two similar plots were established and different watering regimes were applied in order to test for the drought response. Significant variations were observed for all traits within and among populations irrespective of site and watering. Trait variation was larger within than among populations. The effect of drought was neither genotype- nor population-dependent, contrary to the effect of site. The population ranking was maintained in all sites and watering regimes for the two most complex traits: Δ(13)C and growth. Moreover, these two traits were unrelated, which indicates that (i) water-use efficiency and growth are largely uncoupled in this species, and (ii) the environmental factors driving genetic structuration for Δ(13)C and growth act independently. The large variations found within populations combined with the consistent differences among populations suggest a large adaptive potential for P. nigra.

http://www.eje.cz tent and frequency of declines are expected to increase worldwide (Allen et al., 2010; IPCC, 2013). As decline progresses, forest ecosystems undergo dramatic changes in terms of composition, structure and functioning. In particular, there are conspicuous changes in the structure of the canopy that are uncommon in those of healthy trees, such as dead branches and cavities, which increase the structural complexity of the canopy at scale levels of stand, tree and branch (Ishii et al., 2004). However, it may also negatively affect the amount and quality of other critical resources, such as foliage, fruit and seed (Houston, 1981). Such profound structural modifi cations can modulate microclimates, habitat opportunities, and trophic resources for canopy-dwelling communities. For instance, oak decline can promote saproxylic and generalist leaf-feeding beetles, but have a negative effect on specialist leaf-feeders (Sallé et al., 2020). Decline-induced environmental changes can also shape habitat conditions at understory and ground levels. Raphidioptera and Mecoptera are two ancient taxonomic orders of insects frequently encountered in moist temperate forests (Byers & Thornhill, 1983; Aspöck, 2002). Raphidi