Joint IUFRO 7.03.01, 7.03.06 and 7.03.14 Working Party Meeting. Antalya, Turkey, 9-14 April 2014

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  1. Rousselet, J. & Rossi, J.-P., (2014) Landscape genetics: A useful approach to understand population functioning. Joint IUFRO 7.03.01, 7.03.06 and 7.03.14 Working Party Meeting. Antalya, Turkey, 9-14 April 2014
    Résumé : Landscape genetics is a ten years old discipline combining population genetics and landscape ecology. This approach is of a major interest for understanding population functioning, especially in the context of an increasing demand of environmentally-friendly agriculture and forestry. Both conservation biology and agro-ecology, including plant protection against pests and diseases, call for a better understanding of ecological continuities. In comparison with classical population genetics approaches, landscape genetics presents the advantage to explicitly take into account the role of spatial heterogeneities in driving gene flows as well as new insights in dispersal. Here, we review the approach and provide an illustration for a forest pest, the pine processionary moth (PPM). We designed a sampling grid with a mesh size of 16 km covering about 60000 km2 in the southern part of the Paris basin where the moth has colonized wide territories during the last twenty years. This region consists of different land uses, including forests with native broad-leaved trees and exotic conifers, wetland and meadow areas, wide open-fields and large urbanized territories. If we only consider the distribution of the host tree resources, the different habitats of the PPM could be grouped into two main categories: forest lands with large artificial pine stands and non-forest lands with small stands and scattered ornamental pines. Previous field observations suggested that moth expansion could have been accelerated in areas where host trees are scarce whereas large forest stands could have retained philopatric females. We modelled the distribution of the potential host trees using our own inventories of TOFs and forest inventory data from the French institute of geographic and forestry information (IGN). Assuming a philopatric behavior of the moth when large resources are available, this allowed to calculate not only the Euclidian geographic distances between all the cells of our sampling grid, but also the least cost-path distances taking into account the main landscape features for the moth. Moreover, five individuals were collected in each cell and genotyped for eleven microsatellite markers in order to assess the spatial structure of genetic data at a fine scale. The comparison between the matrices of Euclidian and landscape distances and the matrices of genetic distances revealed that gene flow pattern was influenced by the landscape features assumed to play a role. Our results highlight the role of ornamental trees in the expansion of the PPM and call to take into consideration non-forest lands and ‘invisible’ trees in forest health management.

  2. Rossi, J.-P., Garcia, J., Roques, A., Rousselet, J., (2013) Trees outside forest as a critical component of landscape connectivity with regards to forest insects. Joint IUFRO 7.03.01, 7.03.06 and 7.03.14 Working Party Meeting. Antalya, Turkey, 9-14 April 2014
    Résumé : Various species of forest trees are commonly used for ornamental purposes and are therefore frequent in non-forest ecosystems. They constitute an important component of the so-called trees outside forests (TOF). Beyond their beneficial role in biodiversity conservation or their recreational value in urban and peri-urban landscapes, TOFs may also act as elements of ecological continuities and promote pest dissemination, expansion and invasion. This point is essential since urban areas constitute major points of entry for invasive species while both urban forests and the ecological corridors constituted by TOFs tend to favor their expansion. Not much is known, however, about the drivers of TOFs spatial distribution either in urbanized or in agricultural landscapes and only few data are available regarding their role in forest pests dispersion. TOFs are generally absent from forest inventories. The present study focused on the spatial distribution of TOFs across agricultural landscapes and its role in the dispersal of a forest pest insect, the pine processionary moth, Thaumetopoea pityocampa (PPM). This species is a common defoliator occurring on various native and exotic conifer species throughout southern Europe and Mediterranean countries, where it is the most important pine and cedar defoliator. All the TOFs belonging to the genera Pinus, Cedrus and Pseudotsuga were considered as potential hosts. Our first aim was to identify landscape drivers of TOFs distribution and fit a point process model to empirical tree distribution data in a sampling window of 22 × 22 km. We then used the model to simulate TOFs distribution at the scale of a whole ecoregion (100 × 120 km) which facilitated the evaluation of the potential contribution of TOFs to landscape connectivity with regards to PPM dispersal. Various landscape metrics were used to quantify TOF contribution to landscape connectivity. We fitted a non-stationary Poisson process to the empirical data. Ornamental TOFs distribution appeared to be largely driven by the presence of buildings and the “distance to the nearest building” proved to be an accurate covariate in the model. Both empirical and simulated data indicated that TOFs constitute the main source of landscape connectivity in the open-fields under study. Because they do not account for TOFs, forest inventories dramatically underestimated landscape connectivity hence providing an erroneous picture of the PPM habitat distribution. We conclude that TOFs must be taken into account when it comes to understand forest insects landscape dynamics or genetics. TOFs omnipresence also suggests a potentially huge role in pest dispersal and invasive species expansion.


  1. Rousselet, J., Imbault, V., Garcia, J., Lamant, T., Robinet, C., Roques, A., Dowkiw, A., Rossi, J.-P., (2013) Inventaire des arbres-hotes de la processionnaire du pin a l’interface ville-forêt-champs. AFPP – 3e conférence sur l’entretien des espaces verts, jardins, gazons, forêts, zones aquatiques et autres zones non agricoles. Toulouse – 15, 16 et 17 octobre 2013.
    Un inventaire des arbres-hôtes de la processionnaire du pin (Thaumetopoea pityocampa) a été réalisé dans une zone urbaine située entre forêts et open-fields afin d’évaluer le rôle des arbres hors forêts (AHF) dans la circulation de cet insecte à impact économique et sanitaire. Nos résultats montrent que les pins, cèdres et douglas en ville ne représentent numériquement qu’une fraction minime des arbres présents dans la région. Mais, avec une densité de plus d’un arbre et demi à l’hectare, ils sont en quantité suffisante pour générer une bonne connectivité du milieu urbain, d’autant que les arbres les plus attaqués sont les plus plantés. La plus grande proportion de ces arbres se rencontre dans les jardins de particuliers. Des politiques communales visant à gérer les populations de processionnaire du pin en faisant évoluer les pratiques ornementales devront donc nécessairement prendre en considération la composante privée du patrimoine arboré.
    Mots-clés : Thaumetopoea pityocampa, arbre hors forêt, arbre en ville, trames vertes, interface ville-campagne

  2. Rossi, J.-P., Garcia, J., Rousselet, J., (2013) Prendre en compte les arbres ornementaux pour mieux comprendre la perméabilité des paysages a la dispersion des ravageurs. Le cas des arbres hors foret et de la chenille processionnaire du pin. AFPP – 3e conférence sur l’entretien des espaces verts, jardins, gazons, forêts, zones aquatiques et autres zones non agricoles. Toulouse – 15, 16 et 17 octobre 2013.
    Certaines essences forestières sont fortement utilisées en plantation ornementale et sont donc largement présentes en dehors des forêts. Nos travaux ont pour objectif de mieux comprendre la distribution spatiale des arbres hors forêt et leur impact sur la dispersion des organismes ravageurs. Nos résultats démontrent que les arbres hors forêt constituent un facteur de connectivité important et jouent donc un rôle crucial dans la dispersion des ravageurs. Nous présentons le cas de la chenille processionnaire du pin qui soulève d’importants problèmes phytosanitaires et de santé publique.
    Mots-clés : Paysage, dispersion, connectivité, arbres ornementaux, arbres hors forêts, ravageurs