An exhaustive inventory of coniferous trees in an agricultural landscape

Abstract Background Various species of forest trees are commonly used for ornamental purposes and are therefore frequently found in non-forest ecosystems. These trees constitute a significant component of the trees outside forests (TOF). Although increasingly recognized as prominent feature of agricultural lands and built-up areas, not much is known, however, about TOF since they are generally absent from forest inventories. New information In the present study, we focus on the coniferous tree species that constitute potential hosts for a forest defoliator, the pine processionary moth Thaumetopoea pityocampa Den. & Schiff. (Lepidoptera, Notodontidae). We carried out an exhaustive inventory of all pines (Pinus spp.), cedars (Cedrus spp.) and Douglas-fir (Pseudotsuga menziesii) in a 22 × 22 km study window located in the open-field region of Beauce in the centre of France. We recorded a total of 3834 individuals or small groups host trees corresponding a density of 7.9 occurrences per 100 ha. We provide the spatial coordinates of the points without differentiation between tree species.


Introduction
Forest trees are commonly used for ornamental purposes and are therefore frequently found in non-forest ecosystems, especially in urbanized areas. These trees constitute an important component of the so-called trees outside forests (TOF) defined as "trees on land not defined as forest and other wooded land", a definition that is dependent on how forests and woodlands are defined themselves (Kleinn 2000). TOF provide various ecosystem services, e.g., control over soil erosion, nutrient and water cycling, biodiversity conservation or pest control, but despite a growing interest (de Foresta et al. 2013), data documenting TOF are still scarce especially in large open-field agroecosystems. A substantial proportion of TOF are ornamental or amenity trees grown for decorative purposes in gardens and landscape design projects.
In the present study, we focus on the coniferous tree species that are potential hosts for a forest defoliator, the pine processionary moth Thaumetopoea pityocampa Den. & Schiff.
(Lepidoptera, Notodontidae) (thereafter referred to as PPM). T. pityocampa feeds on pines (Pinus spp.), cedars ( Cedrus spp.), and occasionally on Douglas-fir ( Pseudotsuga menziesii) (Cielsa 2011, Roques 2015. The aim of the present survey was to carry out an exhaustive inventory of TOF constituting suitable hosts for the PPM in a 22 × 22 km study window located in the open-field region of Beauce in the centre of France (Fig. 1). Single trees, linear groups of trees and small woodlands were identified and geolocalized, and the resulting data set can be used to assess tree spatial pattern or their contribution to important landscape features (e.g. connectivity) with regards to forest organisms such as the PPM.
The geographical range of the PPM is currently expanding northward in relation to climate change (Roques 2015). During this process, the moth colonizes various non-forest areas where TOF are likely to play a key role by facilitating its dispersal especially in large openfield regions. The data reported here were specifically collected to assess how TOF that are suitable for hosts for the PPM contribute to landscape connectivity for that specie. For that reason, we did not record the tree species identity but only their status as hosts (or not). We used the data set for landscape analyses (Rossi et al. under review) and point process analyses (Rossi and Rousselet 2015). Since tree species were not recorded, we provide here the points locations without any taxonomic taxonomic information. Since -to our knowledge -there is no comparable inventory available in the literature, we publish the data set with the hope that it is useful to other researches such as comparative and/or new data analyses. Sampling description: An exhaustive inventory of PPM host trees outside forests was carried out in a 22 × 22 km = 484 km area located in the north of the Centre region of France (Fig. 1). All trees belonging to the genera Pinus, Cedrus and Pseudotsuga were considered as potential hosts. The study site was located in the southern part of an ecoregion referred to as the Drouais-Thymerais region (

Study plot bounding box
An exhaustive inventory of coniferous trees in an agricultural landscape is easier in winter when deciduous trees have lost their leaves (Rousselet et al. 2013).
Every individual or small group of host trees (single trees, linear groups of trees, small woodlands) was observed by eye, and with binoculars when necessary, from the road and public land. The geographic coordinates were recorded using a Garmin GPS12. The vendor specifies a RMS accuracy of the coordinates to be 15 meters.