Trees outside forests in agricultural landscapes: spatial distribution and impact on habitat connectivity for forest organisms
2016
Rossi, Jean-Pierre | Garcia, Jacques | Roques, Alain | Rousselet, Jérôme | Centre de Biologie pour la Gestion des Populations (UMR CBGP) ; Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut National de la Recherche Agronomique (INRA)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Université de Montpellier (UM)-Institut de Recherche pour le Développement (IRD [Occitanie])-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro) | Unité de recherche Zoologie Forestière (URZF) ; Institut National de la Recherche Agronomique (INRA) | projet ADRIEN (Région Centre), projet Sésame (INRA métaprogramme SMach)
Context: Various species of forest trees are commonly used for ornamental purposes and are therefore frequently found in nonforest ecosystems. They constitute an important component of the so-called trees outside forests (TOF). Not much is known, however, about the drivers of TOF spatial distribution either in urbanized or in agricultural landscapes since they are generally absent from forest inventories.Objective: The present study focused on the spatial distribution of TOF across agricultural landscapes and their potential role in the dispersal of a forest pest insect, the pine processionary moth, [i]Thaumetopoea pityocampa[/i] (PPM).Methods: All the TOF belonging to the genera [i]Pinus[/i],[i]Cedrus[/i] and [i]Pseudotsuga[/i] were considered as potential hosts and inventoried within a 22 9 22 km study window. We fitted a nonstationary Poisson process to the empirical data and used the distance to the nearest building as a covariate.Results: Both empirical and simulated data indicated that TOF associated to human artifacts/urbanized areas constituted the main source of landscape connectivity for the PPM in the open fields under study. Because they do not account for TOF, forest inventories dramatically underestimate landscape connectivity and provide an erroneous picture of the PPM habitat distribution.Conclusions: We conclude that TOF, especially the ornamental component, must be taken into account when it comes to understanding forest insect landscape dynamics or genetics. The omnipresence of TOF also suggests a potentially huge role in pest dispersal and invasive species expansion.
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