Abstract• This article synthesizes and reviews the available information on the effects of forestry practices on the occurrence of biotic and abiotic hazards, as well as on stand susceptibility to these damaging agents, concentrating on mammal herbivores, pest insects, pathogenic fungi, wind and fire.• The management operations examined are site selection, site preparation, stand composition, regeneration method, cleaning and weed control, thinning and pruning, and harvesting. For each of these operations we have examined how they influence the occurrence of biotic and abiotic damaging agents, the susceptibility of European forests, and describe the ecological processes that may explain these influences.• Overall, we find that the silvicultural operations that have the largest influence on both biotic and abiotic risks to European forest stands are closely related to species composition and the structure of the overstorey. Four main processes that drive the causal relationships between stand management and susceptibility have been identified: effect on local microclimate, provision of fuel and resources to biotic and abiotic hazards, enhancement of biological control by natural enemies and changes in individual tree physiology and development.• The review demonstrates an opportunity to develop silvicultural methods that achieve forest management objectives at the same time as minimising biotic and abiotic risks. Mots-clés :sylviculture / peuplement / occurrence / sensibilité / Résumé -Influences de la sylviculture sur le risque de dégâts biotiques et abiotiques dans les peuplements forestiers.• Cette revue bibliographique s'intéresse aux effets de la sylviculture sur la sensibilité des peuplements forestiers aux principaux agents de dégâts biotiques et abiotiques que sont les mammifères herbivores, les insectes ravageurs, les champignons pathogènes, le feu et les vents forts. * Corresponding author: herve.jactel@pierroton.inra.frArticle published by EDP Sciences Ann. For. Sci. 66 (2009) 701 H. Jactel et al.• Les pratiques forestières analysées sont la sélection et la préparation des sites de reboisement, la définition de la composition en essences et le choix du matériel génétique, les méthodes de régé-nération et d'entretien, les modalités d'éclaircie et d'élagage, le mode de récolte finale. L'influence de chacune de ces opérations sur l'occurrence des agents de dégâts biotiques et abiotiques et sur la sensibilité des peuplements est examinée ainsi que les processus écologiques sous-jacents.• Les opérations sylvicoles qui se révèlent les plus déterminantes pour la sensibilité des forêts en Europe sont celles qui affectent la composition et la structure de la strate arborée. Quatre principaux processus écologiques semblent expliquer la relation entre sylviculture et sensibilité des peuplements : la modification du micro-climat, l'apport de ressources ou de combustible aux agents de dégâts, l'amélioration du contrôle biologique par les ennemis naturels et l'altération de la physiologie et du développement des arb...

Allochronic speciation refers to a mode of sympatric speciation in which the differentiation of populations is primarily due to a phenological shift without habitat or host change. However, it has been so far rarely documented. The present paper reports on a plausible case of allochronic differentiation between sympatric populations of the pine processionary moth (PPM), Thaumetopoea pityocampa. The PPM is a Mediterranean insect with winter larval development. A phenologically atypical population with early adult activity and summer larval development was detected 10 years ago in Portugal. Mitochondrial and nuclear sequences strongly suggest that the 'summer' individuals are closely related to the sympatric winter population, while microsatellite data show a reduction in allelic richness, a distortion of allelic frequencies and significant genetic differentiation. Moreover, monitoring of adult flights suggests that reproductive activity does not overlap between the summer and winter populations. We postulate that the summer population appeared after a sudden phenological shift of some individuals of the sympatric winter population, leading to a founder effect and complete reproductive isolation. Given that the individuals showing this new phenology are subject to different selection pressures, the observed allochronic differentiation may rapidly lead to deeper divergence.

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A plausible case of allochronic differentiation, where barrier to gene flow is primarily attributable to a phenological shift, was recently discovered in Portugal for the pine processionary moth Thaumetopoea pityocampa. Previous results suggested that the observed ‘summer population’ (SP) originated from the sympatric winter population (WP). Our objectives were to finely analyse these patterns and test their stability in time, through field monitoring and genetic analyses of larvae and adults across different years. Reproductive activity never overlapped between SP and WP. Microsatellites showed a clear differentiation of the SP, consistent with a strong reduction in gene flow owing to the phenological shift. Assignment tests suggested that some individuals shift from the SP to the WP phenology, causing some hybridization. We discuss these patterns and their maintenance over time. This could be a first stage of allochronic speciation, and SP should be considered as a distinct phenological race.

Native to Australasia, Eucalyptus (sensu lato) is one of the most planted genera of trees in the world. However, the sustainability of Eucalyptus species as plantation trees in non-native areas is increasingly threatened by the introduction and spread of Eucalyptus-feeding insects fromAustralia. We examine patterns and potential trends with respect to the global spread of Eucalyptusfeeding insects. Likely pathways of introduction and drivers of the rapid distribution of these insects, as well as management options are considered. The rate of introductions is shown to have increased nearly fivefold since the 1980s. As a result, the number of non-native pests of eucalypts outside of Australia has doubled in less than three decades. Furthermore, the rate of secondary spread among continents has also increased. Surprisingly, we found no association between area planted and the number of pests or new introductions. Only a small number of countries have been the points of first detection outside the native range; these countries have acted as bridgeheads to other regions.Quarantine regulations aimed at reducing the spread of invasive organisms appear to be ineffective at a global scale, and pathways allowing these invasions to occur are poorly understood or unknown. An expanded suite of management options are needed to provide resilience against the rapid accrual and homogenization of eucalypt pests, thereby ensuring the sustainability of eucalypt forestry worldwide.

A process of adaptive divergence for tolerance to high temperatures was identified using a rare model system, consisting of two sympatric populations of a Lepidoptera (Thaumetopoea pityocampa) with different life cycle timings, a ‘mutant’ population with summer larval development, Leiria SP, and the founder natural population, having winter larval development, Leiria WP. A third, allopatric population (Bordeaux WP) was also studied. First and second instar larvae were experimentally exposed to daily‐cycles of heat treatment reaching maximum values of 36, 38, 40 and 42 °C; control groups placed at 25 °C. A lethal temperature effect was only significant at 42 °C, for Leiria SP, whereas all temperatures tested had a significant negative effect upon Leiria WP, thus indicating an upper threshold of survival c.a. 6 °C above that of the WP. Cox regression model, for pooled heat treatments, predicted mortality hazard to increase for Leiria WP (+108%) and Bordeaux WP (+78%) in contrast to Leiria SP; to increase by 24% for each additional °C; and to decrease by 53% from first to second instar larvae. High variability among individuals was observed, a population characteristic that may favour selection and consequent adaptation. Present findings provide an example of ecological differentiation, following a process of allochronic divergence. Results further contribute to a better understanding of the implications of climate change for ecological genetics.

1. Exotic tree species are widely used in forest plantations for their often high productivity and performance compared to native trees. However, these advantages may be compromised by herbivore damage. 2. A list of European insect species that have expanded their host range to one of 28 exotic tree species introduced to Europe was compiled from a systematic literature review. The number of successful expansions was analysed using three predictors: (i) phylogenetic relatedness between exotic and European tree species; (ii) area covered by exotic tree species in Europe; and (iii) time since their introduction into Europe. 3. In total, 590 host expansions of native insects to exotic trees were found, mainly of polyphagous species (43%); 25% of the cases reported some type of damage. Bark and wood borers, and defoliators were the dominant guilds. 4. The number of recruited native insect species and cases where major damage occurred was positively correlated with the geographical extent of exotic trees in Europe and the presence of congeneric native trees. 5. Synthesis and applications. The use of exotic tree species creates opportunities for native insect herbivores to expand their host range and increase their damage if they are widely planted next to native congeners. Risk assessment studies are recommended when introducing new tree species for forestry plantations. Risk assessments should include trials on susceptibility to any potential damaging organisms in the introduced range.