Losses of natural and semi-natural forests, mostly to agriculture, are a signiWcant concern for biodiversity. Against this trend, the area of intensively managed plantation forests increases, and there is much debate about the implications for biodiversity. We provide a comprehensive review of the function of plantation forests as habitat compared with other land cover, examine the eVects on biodiversity at the landscape scale, and synthesise context-speciWc eVects of plantation forestry on biodiversity. Natural forests are usually more suitable as habitat for a wider range of native forest species than plantation forests but there is abundant evidence that plantation forests can provide valuable habitat, even for some threatened and endangered species, and may contribute to the conservation of biodiversity by various mechanisms. In landscapes where forest is the natural land cover, plantation forests may represent a low-contrast matrix, and aVorestation of agricultural land can assist conservation by providing complementary forest habitat, buVering edge eVects, and An 'oxymoron' is a Wgure of speech using an intended combination of two apparently contradictory terms. 926Biodivers Conserv (2008) 17:925-951 1 C increasing connectivity. In contrast, conversion of natural forests and aVorestation of natural non-forest land is detrimental. However, regional deforestation pressure for agricultural development may render plantation forestry a 'lesser evil' if forest managers protect indigenous vegetation remnants. We provide numerous context-speciWc examples and case studies to assist impact assessments of plantation forestry, and we oVer a range of management recommendations. This paper also serves as an introduction and background paper to this special issue on the eVects of plantation forests on biodiversity.

Biodiversity loss from plant communities is often acknowledged to affect primary production but little is known about effects on herbivores. We conducted a meta-analysis of a worldwide data set of 119 studies to compare herbivory in single-species and mixed forests. This showed a significant reduction of herbivory in more diverse forests but this varied with the host specificity of insects. In diverse forests, herbivory by oligophagous species was virtually always reduced, whereas the response of polyphagous species was variable. Further analyses revealed that the composition of tree mixtures may be more important than species richness per se because diversity effects on herbivory were greater when mixed forests comprised taxonomically more distant tree species, and when the proportion of non-host trees was greater than that of host trees. These findings provide new support for the role of biodiversity in ecosystem functioning across trophic levels.

Trade in live plants has been recognized worldwide as an important invasion pathway for non‐native plant pests. Such pests can have severe economic and ecological consequences. Nearly 70% of damaging forest insects and pathogens established in the US between 1860 and 2006 most likely entered on imported live plants. The current regulation of plant imports is outdated and needs to balance the impacts of pest damage, the expense of mitigation efforts, and the benefits of live plant importation. To inform these discussions, we document large increases in the volume and value of plant imports over the past five decades and explain recent and proposed changes to plant import regulations. Two data sources were used to estimate the infestation rate of regulated pests in live plant shipments entering the US, thus allowing evaluation of the efficacy of the current port inspection process.

Insect species associated with human goods continue to be accidentally introduced into new locations. A small proportion of these introduced species become invasive, causing a range of impacts in the receiving community.

Our ability to predict the identity of future invasive alien species is largely based upon knowledge of prior invasion history. Emerging alien species-those never encountered as aliens before-therefore pose a significant challenge to biosecurity interventions worldwide. Understanding their temporal trends, origins, and the drivers of their spread is pivotal to improving prevention and risk assessment tools. Here, we use a database of 45,984 first records of 16,019 established alien species to investigate the temporal dynamics of occurrences of emerging alien species worldwide. Even after many centuries of invasions the rate of emergence of new alien species is still high: One-quarter of first records during 2000-2005 were of species that had not been previously recorded anywhere as alien, though with large variation across taxa. Model results show that the high proportion of emerging alien species cannot be solely explained by increases in well-known drivers such as the amount of imported commodities from historically important source regions. Instead, these dynamics reflect the incorporation of new regions into the pool of potential alien species, likely as a consequence of expanding trade networks and environmental change. This process compensates for the depletion of the historically important source species pool through successive invasions. We estimate that 1-16% of all species on Earth, depending on the taxonomic group, qualify as potential alien species. These results suggest that there remains a high proportion of emerging alien species we have yet to encounter, with future impacts that are difficult to predict.

Forests are critical habitats for biodiversity and they are also essential for the provision of a wide range of ecosystem services that are important to human well-being. There is increasing evidence that biodiversity contributes to forest ecosystem functioning and the provision of ecosystem services. Here we provide a review of forest ecosystem services including biomass production, habitat provisioning services, pollination, seed dispersal, resistance to wind storms, fire regulation and mitigation, pest regulation of native and invading insects, carbon sequestration, and cultural ecosystem services, in relation to forest type, structure and diversity. We also consider relationships between forest biodiversity and multifunctionality, and trade-offs among ecosystem services. We compare the concepts of ecosystem processes, functions and services to clarify their definitions. Our review of published studies indicates a lack of empirical studies that establish quantitative and causal relationships between forest biodiversity and many important ecosystem services. The literature is highly skewed; studies on provisioning of nutrition and energy, and on cultural services, delivered by mixed-species forests are under-represented. Planted forests offer ample opportunity for optimising their composition and diversity because replanting after harvesting is a recurring process. Planting mixed-species forests should be given more consideration as they are likely to provide a wider range of ecosystem services within the forest and for adjacent land uses. This review also serves as the introduction to this special issue of Biodiversity and Conservation on various aspects of forest biodiversity and ecosystem services.

Several key tree genera are used in planted forests worldwide, and these represent valuable global resources. Planted forests are increasingly threatened by insects and microbial pathogens, which are introduced accidentally and/or have adapted to new host trees. Globalization has hastened tree pest emergence, despite a growing awareness of the problem, improved understanding of the costs, and an increased focus on the importance of quarantine. To protect the value and potential of planted forests, innovative solutions and a better-coordinated global approach are needed. Mitigation strategies that are effective only in wealthy countries fail to contain invasions elsewhere in the world, ultimately leading to global impacts. Solutions to forest pest problems in the future should mainly focus on integrating management approaches globally, rather than single-country strategies. A global strategy to manage pest issues is vitally important and urgently needed.

Scolytinae species are among the most damaging forest pests, and many of them are invasive. Over 1500 Scolytinae interceptions were recorded at New Zealand's borders between 1950 and 2000. Among the 103 species were Dendroctonus ponderosae, Ips typographus, and other high-risk species, but actual arrivals probably included many more species. Interceptions were primarily associated with dunnage, casewood (crating), and sawn timber, and originated from 59 countries, mainly from Europe, Australasia, northern Asia, and North America. New Zealand and United States interception data were highly correlated, and 7 of the 10 most intercepted species were shared. Interception frequency and establishment in New Zealand were not clearly related. By combining New Zealand and United States interceptions of true bark beetles we obtained data on species found in shipments from around the world. Logistic regression analysis showed that frequently intercepted species were about four times as likely as rarely intercepted species to be established somewhere. Interception records of wood and bark borers are valuable for the prediction of invaders and for our general understanding of invasions. The use of alternatives to solid wood packaging, such as processed wood, should be encouraged to reduce the spread of invasive wood and bark borers. Résumé : Les scolytinés sont parmi les ravageurs forestiers les plus dommageables et ils comptent plusieurs espèces envahissantes. Plus de 1500 interceptions de scolytinés ont été enregistrées aux frontières de la Nouvelle-Zélande entre 1950 et 2000. Parmi les 103 espèces, on trouvait Dendroctonus ponderosae, Ips typographus et d'autres espèces à haut risque mais les arrivées incluaient en réalité probablement beaucoup plus d'espèces. Les interceptions étaient principalement associées au bois d'arrimage, au bois de caisserie (emballages à claire-voie) et au bois scié et provenaient de 59 pays, surtout de l'Europe, de l'Australasie, du nord de l'Asie et de l'Amérique du Nord. Les données d'interception de la Nouvelle-Zélande et des États-Unis étaient étroitement corrélées et sept des dix espèces les plus souvent interceptées étaient communes. En Nouvelle-Zélande, la fréquence d'interception et l'établissement n'étaient pas clairement reliés.En combinant les interceptions des scolytes de l'écorce faites en Nouvelle-Zélande et aux États-Unis, les auteurs ont obtenu des données sur les espèces retrouvées dans les expéditions partout dans le monde. L'analyse de régression logistique a démontré que les espèces fréquemment interceptées avaient environ quatre fois plus de chances d'être éta-blies quelque part que les espèces rarement interceptées. Les données d'interception des xylophages et des insectes qui s'attaquent à l'écorce sont précieuses pour faire des prédictions au sujet des envahisseurs et pour notre compréhension générale des envahissements. L'utilisation de solutions de rechange à l'empaquetage avec du bois solide, telles que le bois transformé, devrait être encouragée pour réduire la dispers...