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For forest sustainability and vulnerability assessment, the landscape scale is considered to be more and more relevant as the stand level approaches its known limitations. This review, which describes the main forest landscape simulation tools used in the 20 European case studies of the European project “Future-oriented integrated management of European forest landscapes” (INTEGRAL), gives an update on existing decision support tools to run landscape simulation from Mediterranean to boreal ecosystems. The main growth models and software available in Europe are described, and the strengths and weaknesses of different approaches are discussed. Trades-offs between input efforts and output are illustrated. Recommendations for the selection of a forest landscape simulator are given. The paper concludes by describing the need to have tools that are able to cope with climate change and the need to build more robust indicators for assessment of forest landscape sustainability and vulnerability. The INTEGRAL project has received funding from the European Union’s Seventh Programme for research, technological development and demonstration under grant agreement No. 282887. http://www. integral-project.eu/. Moreover, financial support by the Transnational Access to Research Infrastructures activity in the 7th Framework Programme of the EC under the Trees4Future project (No. 284181) for conducting the research is gratefully acknowledged. This research has also received funding from the European Union H2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 691149 (SuFoRun). Researcher Jordi Garcia-Gonzalo was supported by a “Ramon y Cajal” research contract from the MINECO (Ref. RYC-2013-14262) and has received funding from CERCA Programme/Generalitat de Catalunya. This paper could be achieved thanks to support of EFIATLANTIC donors: Conseil regional d’Aquitaine, Ministère de l’agriculture et de la forêt.

International audience; Mixed forests are thought to be less prone to pest insect damage than monocultures. This may result from reduced host availability (i.e., density effect) or from non-host trees reducing the physical or chemical apparency of host trees (i.e., associational resistance, AR). However, associational and density effects are often confounded in mixed forests. We aimed to disentangle their relative contribution to attacks of pine trees by a specialist pest, the pine processionary moth (PPM, Thaumetopoea pityocampa). We assessed pine infestation by PPM by counting the number of winter nests during three consecutive years along an experimental gradient of pine density in presence or absence of a fast growing species, namely birch. The total number of PPM nests per plot increased with pine density (maximum in high density monocultures), while the proportion of attacked pine trees decreased along the same gradient. Birch provided associational resistance via reduced pine apparency due to their greatest higher. This mechanism occurred at two spatial scales, whenever birch was planted within pine plots or in adjacent plots. Associational resistance was stronger in dense stands, probably due to reduced distance between pines and neighboring birches. But AR faded with time, pines becoming taller than birches, making density effects preeminent over apparency effects. Our findings suggest that mixing tree species to trigger resistance to pest insects requires taking into account the relative growth rate of associated species together with the relative proportion of associated species, both within and between stands. © 2016 Elsevier B.V.

International audience; Die Reduktion von Pflanzenfraß durch Insekten ist eine der Leistungen, die von der Baumdiversität in Waldökosystemen erbracht wird. Während zunehmend anerkannt wird, dass die Zusammensetzung von Baumgemeinschaften eine wichtige Rolle beim Auslösen von gemeinschaftlicher Abwehr gegen Herbivore spielt, ist über die zugrunde liegenden Mechanismen wenig bekannt. Wir untersuchten diese Frage im ORPHEE-Experiment, indem wir den Befall durch den Pinienprozessionsspinner (Thaumetopoea pityocampa) über einen Gradienten von Monokultur bis zur Fünf-Arten-Mischung registrierten. Wir zeigten, dass der Baum-Artenreichtum per se keinen Einfluss auf die Befallswahrscheinlichkeit hatte. Dagegen hingen die Befallsraten stark von der Zusammensetzung der Bestände ab. Systeme von Pinie (Pinus pinaster) und Birke (Betula pendula) wurden weniger stark befallen, während Mischungen von Pinien und Eichen (Quercus spp) häufiger als Reinbestände von Pinien attackiert wurden. Wenn man die relative Höhe von Pinien und der vergesellschafteten Laubbaumarten in Betracht zieht, könnte dieser Effekt mit der Apparenz der Pinien erklärt werden. Die Pinien waren im Mittel 343 ± 5 cm hoch. Die Birken waren als schnellwachsende Bäume etwas höher 363 ± 6 cm) als die Pinien, während die Eichen bedeutend kleiner waren (74 ± 1 cm). Die Wirtsbäume von T. pityocampa waren damit in den Mischbeständen von Pinie und Birke teilweise verborgen, traten bei Vergesellschaftung mit Eichen aber deutlicher in Erscheinung. Wir meinen deshalb, dass die verminderte Apparenz der Pinien visuelle Signale stört, die von den Weibchen genutzt werden, um vor der Eiablage Wirtsbäume auszuwählen. Diese Untersuchung macht deutlich, dass es notwendig ist, Eigenschaften wie die Wachstumsgeschwindigkeit zu berücksichtigen, wenn die Baumarten für eine Mischkultur ausgewählt werden, um die Abwehr eines Forstbestandes gegen Schadinsekten zu verbessern.; The reduction of insect herbivory is one of the services provided by tree diversity in forest ecosystems. While it is increasingly acknowledged that the compositional characteristics of tree species assemblages play a major role in triggering associational resistance to herbivores, underlying mechanisms are less well known. We addressed this question in the ORPHEE experiment by assessing pine processionary moth infestations (Thaumetopoea pityocampa) across a tree diversity gradient from pine monocultures to five species mixtures. We showed that tree species richness per se had no effect on the probability of attack by this pest. By contrast, the infestation rate was strongly dependent on plot composition. Mixtures of pines (Pinus pinaster) and birches (Betula pendula) were less prone to T. pityocampa infestations, whereas mixtures of pines and oaks (Quercus spp.) were more often attacked than pine monocultures. By taking into account the relative height of pines and associated broadleaved species, this effect could be explained by pine apparency. Pines were on average 343 ± 5 cm height. Birches, as fast growing trees, were slightly taller than pines (363 ± 6 cm), while oak trees were significantly smaller (74 ± 1 cm). Host trees of T. pityocampa were then partly hidden in mixtures of pines and birches but more apparent in mixtures with oaks. We suggest that reduced pine apparency disrupted visual cues used by female moths to select host trees prior to oviposition. This study highlights the need to take into account tree traits such as growth rate when selecting the tree species that have to be associated in order to improve forest resistance to pest insects.

International audience; The pine processionary moth (PPM, Thaumetopoea pityocampa) is the main defoliator of pines in the Mediterranean area, necessitating constant surveillance and regular pest management. A sound understanding of the spatial distribution of infested trees, both within and between stands, is required to increase management efficiency. We hypothesized that both host tree density at stand scale and tree apparency at individual tree scale were responsible for between- and within-stand patterns of PPM infestation. We tested these hypotheses on a sample of 171 maritime pine stands in the Landes de Gascogne, the largest plantation forest in Europe. We showed that PPM infestation (percentage of infested trees) decreased significantly with stand density, and was therefore greater in older than in younger stands. The probability of a pine tree being attacked increased significantly with tree height and proximity to the edge of the stand. Mortality rates of exposed sentinel egg batches did not differ with distance from the stand edge. We discuss three likely explanations for higher infestation of taller trees at stand edges: better survival of larvae on sun-exposed trees, and random interception vs. active host selection by gravid females. Our findings suggest that stand management could be adapted in order to decrease the risk of damage by the pine processionary moth, and that predictive tools for infestation dynamics can be based on forest growth models.