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Abstract. 1. Trees outside forests (TOFs) are declining in agricultural landscapes worldwide. Although they provide valuable habitats for saproxylic species, their relative contribution to saproxylic biodiversity with respect to forests is poorly known. Our aim was to investigate the conservation value of oak TOFs for saproxylic beetles in European agricultural landscapes.2. In our design, plots pairing forest trees and TOFs were sampled in sites nested in two French regions. We studied local habitat conditions (deadwood, tree-related microhabitats, openness) and saproxylic beetle assemblages. We measured significant environmental contrasts between forest trees and TOFs, and found that the latter hosted higher microhabitat density and diversity.3. Species assemblages were strongly dissimilar between TOFs and forest trees. Even though a-diversity and abundance were not significantly different in the two contexts, the between-tree b-diversity and the c-diversity of both all and rare species were higher outside than inside forests.4. Furthermore, the potential key drivers of saproxylic beetle diversity were not consistent between forest trees and TOFs. Tree cavity was the only elementary microhabitat whose density significantly affected biodiversity metrics both inside and outside forests. Many more effects on beetle assemblages originating from surrounding conditions were observed in TOFs than in forest trees. We also confirmed that saproxylic beetle diversity is significantly associated to canopy openness.5. Consistent with our results, environmentally friendly forestry practices should include the retention of sun-exposed microhabitat-bearing trees at final harvesting. In addition, environmental policies should favour TOFs as well as oak savanna-like woodlands which are seriously threatened worldwide.

The decline of many saproxylic species results from the decrease in old-growth structures in European harvested forests. Among conservation tools, protected reserves withdrawn from regular harvesting and extended rotations have been employed to restore old-growth attributes in structurally simplified managed forests, even if the effects of such management actions on forest habitats and biodiversity remain largely unknown.In this study, we compared structural stand features and saproxylic beetle assemblages in two stand classes -recently harvested stands and long-established reserves, where less or more than 30 years had elapsed since last harvest. Habitat and saproxylic beetle data were collected according to standardized protocols in 153 plots in seven lowland deciduous forests.Tangible contrasts in stand features were found between long-established reserves and recently harvested plots. Indeed, most higher-value densities and volumes were found in unharvested areas. The difference was weaker for microhabitat-bearing tree density than for deadwood; some deadwood features, such as volume of large downed and standing deadwood showed a very pronounced difference, thus indicating a marked deleterious effect of forest harvesting on these elements. Deadwood diversity, on the other hand, was only slightly affected and the level of stand openness did not change.The response of saproxylic beetles to delayed harvesting was weaker than the structural changes in deadwood features. Indeed even if only some guilds weakly increased in non-harvested plots, harvesting classes significantly affected the abundance of a quarter of the species tested.Our results tend to question measures such as rotating and temporarily ageing patches. We argue in favor of permanent strict fixed-location reserves. Future work should examine how stands recover old-growth forest attributes and how the associated saproxylic fauna colonizes in the long term. bs_bs_banner Animal Conservation. Print ISSN 1367-9430 Set-aside forests and saproxylic beetles C. Bouget et al. Set-aside forests and saproxylic beetles C. Bouget et al.

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.

Saproxylic beetles – associated with dead wood or with other insects, fungi and microorganisms that decompose it – play a major role in forest nutrient cycling. They are important ecosystem service providers and are used as key bio-indicators of old-growth forests. In France alone, where the present study took place, there are about 2500 species distributed within 71 families. This high diversity represents a major challenge for specimen sorting and identification.The PASSIFOR project aims at developing a DNA metabarcoding approach to facilitate and enhance the monitoring of saproxylic beetles as indicators in ecological studies. As a first step toward that goal we assembled a library of DNA barcodes using the standard genetic marker for animals, i.e. a portion of the COI mitochondrial gene. In the present contribution, we release a library including 656 records representing 410 species in 40 different families. Species were identified by expert taxonomists, and each record is linked to a voucher specimen to enable future morphological examination. We also highlight and briefly discuss cases of low interspecific divergences, as well as cases of high intraspecific divergences that might represent cases of overlooked or cryptic diversity.

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Monitoring saproxylic beetle diversity, though challenging, can help identifying relevant conservation sites or key drivers of forest biodiversity, and assessing the impact of forestry practices on biodiversity. Unfortunately, monitoring species assemblages is costly, mainly due to the time spent on identification. Excluding families which are rich in specimens and species but are difficult to identify is a frequent procedure used in ecological entomology to reduce the identification cost. The Staphylinidae (rove beetle) family is both one of the most frequently excluded and one of the most species-rich saproxylic beetle families. Using a large-scale beetle and environmental dataset from 238 beech stands across Europe, we evaluated the effects of staphylinid exclusion on results in ecological forest studies. Simplified staphylinid-excluded assemblages were found to be relevant surrogates for whole assemblages. The species richness and composition of saproxylic beetle assemblages both with and without staphylinids responded congruently to landscape, climatic and stand gradients, even when the assemblages included a high proportion of staphylinid species. At both local and regional scales, the species richness as well as the species composition of staphylinid-included and staphylinid-excluded assemblages were highly positively correlated. Ranking of sites according to their biodiversity level, which either included or excluded Staphylinidae in species richness, also gave congruent results. From our results, species assemblages omitting staphylinids can be taken as efficient surrogates for complete assemblages in large scale biodiversity monitoring studies.