Retention forestry implies that biological legacies like dead and living trees are deliberately selected and retained beyond harvesting cycles to benefit biodiversity and ecosystem functioning. This model has been applied for several decades in even-aged, clearcutting (CC) systems but less so in uneven-aged, continuous-cover forestry (CCF). We provide an overview of retention in CCF in temperate regions of Europe, currently largely focused on habitat trees and dead wood. The relevance of current meta-analyses and many other studies on retention in CC is limited since they emphasize larger patches in open surroundings. Therefore, we reflect here on the ecological foundations and socio-economic frameworks of retention approaches in CCF, and highlight several areas with development potential for the future. Conclusions from this perspective paper, based on both research and current practice on several continents, although highlighting Europe, are also relevant to other temperate regions of the world using continuous-cover forest management approaches.Electronic supplementary materialThe online version of this article (10.1007/s13280-019-01190-1) contains supplementary material, which is available to authorized users.

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Insect populations are globally declining but standardized long‐term data to evaluate trends and consequences are largely missing. One difficulty among many is the rather narrow taxonomic cover of most conventional trap types, which makes the use of several complementary collection methods necessary to achieve comprehensive coverage. To avoid the effort associated with operating multiple traps, we demonstrate how to modify window traps in a simple and standardizable way to capture a wider range of flying insect taxa. While a typical window trap only has a collection unit below the windows, we added an additional collection unit on top of the windows. We tested this modified trap design in 135 study plots in a temperate forest over 5 months and compared trap catches between top and bottom collection units. The top collection unit captured considerably more individuals of Hymenoptera, Diptera, Lepidoptera, Neuroptera, Auchenorrhyncha and Thysanoptera than the bottom collection unit. In contrast, there were more individuals of Coleoptera, Heteroptera, Sternorrhyncha and Psocoptera in the bottom collection unit. Both collection units captured a highly distinct insect community and patterns were consistent throughout the season. These modified traps are suitable for collecting a broader range of flying insects compared to conventional window traps. The additional top unit is fast and easy to build and the traps require little maintenance while operating in the field. These characteristics make modified window traps with top and bottom collection units a promising tool for standardized and replicable biodiversity studies covering a broad range of insect taxa.

Crop plant domestication can change plant resistance to herbivores leading to differences in pest pressure experienced by crop plants and their wild relatives. To compare resistance to herbivores between domesticated and wild fruit trees, we quantified direct resistance and indirect resistance to a pest insect, the florivorous apple blossom weevil Anthonomus pomorum (Coleoptera: Curculionidae), for the cultivated apple Malus domestica and two wild apple species, the European crab apple M. sylvestris and the exotic M. kirghisorum. We measured weevil infestation and performance (weight, sex ratio), and weevil parasitism by parasitoid wasps for different cultivars of M. domestica and for the two wild apple species. To explain weevil and parasitoid responses to different apple species, we quantified tree characteristics including nitrogen content, size of flower buds, bark roughness, tree size, tree phenology and tree position. We found significant differences in susceptibility to weevil infestation between apple species, with lowest infestation (highest apple resistance) in M. domestica and highest infestation in M. kirghisorum. The suitability of apple species also varied significantly: weevils emerging from M. sylvestris were significantly lighter than those from M. kirghisorum. Parasitism of A. pomorum by different parasitoid species was significantly higher in M. sylvestris than in M. domestica. Infestation, weevil weight and parasitism were positively related to tree characteristics: infestation to bud nitrogen content and bark roughness, weevil size to nitrogen content and bud size, and parasitism to tree height and bud density. Our study revealed marked differences between apple species in susceptibility and suitability for the pest herbivore, but also for antagonistic parasitoids. Whereas direct resistance appeared to be higher in cultivated apple, indirect resistance via parasitoids was apparently higher in wild apple trees. Our findings suggest that wild and cultivated apple trees possess different resistance traits that may be combined to optimize resistance in commercial apple cultivars.

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