References of "Lejeune, Philippe"
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See detailGrille : Plugin de création de grilles d'échantillonnage pour le logiciel QGIS
De Thier, Olivier ULg; Handerek, Daphné ULg; Modave, Maxime et al

Software (2015)

Le plugin Grille pour QGIS est destiné à définir et créer des grilles d’échantillonnage dans le cadre d’inventaires et de recensements appliqués à la gestion des ressources naturelles.

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See detailForEstimator
Dedry, Laurent ULg; De Thier, Olivier ULg; Perin, Jérôme ULg et al

Software (2015)

ForEstimator est un plugin (une extension) QGIS qui permet d'estimer la hauteur dominante de peuplements résineux en Wallonie.

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See detailA novel procedure to measure shrinkage-free tree-rings from very large wood samples combining photogrammetry, high-resolution image processing, and GIS tools
Latte, Nicolas ULg; Beeckman, Hans; Bauwens, Sébastien ULg et al

in Dendrochronologia (2015), 34

We present a new procedure for wood sampling and tree-ring measurement that can be used for dendrochronological investigation on very large trees, specifically adapted for tropical rainforest species ... [more ▼]

We present a new procedure for wood sampling and tree-ring measurement that can be used for dendrochronological investigation on very large trees, specifically adapted for tropical rainforest species. This procedure takes advantage of the technological developments in computing, image processing, and geographic information systems (GIS) to overcome the technical limitations of the currently used methods. Two types of wood samples can be used (stem disks and/or bars) depending on tree diameter, and the difficulty of ring delineation and crossdating. Bars are an effective compromise between cores and disks. We developed an application combining several programs (Excel, R, ArcGIS, and MapWinGIS) in the Windows operating system for semi-automatic measurement of tree-rings from high-resolution images of the sanded cross-section. Using an innovative method to reverse the wood shrinkage resulting from the drying process, tree-ring measurement can be performed on shrinkage-free images, thus referring to the actual growth of the tree. [less ▲]

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See detailDétection de l'érosion dans un bassin versant agricole par comparaison d'images multidates acquises par drone
Lisein, Jonathan ULg; Pineux, Nathalie ULg; Pierrot-Deseilligny, marc et al

Scientific conference (2015, March 26)

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See detailNineteenth century human history explains the dominance of light-demanding tree species in Central African moist forests
Morin, Julie ULg; Fayolle, Adeline ULg; Favier, Charly et al

Poster (2015, March 21)

The canopy of central African moist forests is dominated by light-demanding trees. Most of these species show a distribution of diameters that indicates a regeneration shortage. Here we show through the ... [more ▼]

The canopy of central African moist forests is dominated by light-demanding trees. Most of these species show a distribution of diameters that indicates a regeneration shortage. Here we show through the combined analysis of botanical, palaeoecological, archaeological and historical data that most of these trees are not older than ca. 180 years. This age corresponds to the early 19th century (around 1830) when the slave-raiding, the interethnic wars and the colonization of the inlands by the Europeans disturbed the human spatial occupancy. After 1885, the spatial clumping of people and villages along the main communication axes induced less itinerancy in the forest. We believe that former activities such as shifting cultivation created scattered openings in the canopy, large enough to allow light-demanding trees to establish. Nowadays, common logging operations do not create openings sufficiently large for the regeneration of these high value timber species. Our findings emphasize the need to include considerations about the history of human spatial occupancy and activities to understand forest dynamics. We need silvicultural guidelines adapted to the autecology of the species. Population enforcements (e.g. enrichment) will be needed to ensure the sustainability of timber yields in forests dominated by long-lived light-demanding trees. [less ▲]

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See detailHow Tightly Linked Are Pericopsis elata (Fabaceae) Patches to Anthropogenic Disturbances in Southeastern Cameroon?
Bourland, Nils; Cerisier, François; Daïnou, Kasso ULg et al

in Forests (2015), 6(2), 293-310

While most past studies have emphasized the relationships between specific forest stands and edaphic factors, recent observations in Central African moist forests suggested that an increase of slash-and ... [more ▼]

While most past studies have emphasized the relationships between specific forest stands and edaphic factors, recent observations in Central African moist forests suggested that an increase of slash-and-burn agriculture since 3000–2000 BP (Before Present) could be the main driver of the persistence of light-demanding tree species. In order to examine anthropogenic factors in the persistence of such populations, our study focused on Pericopsis elata, an endangered clustered timber species. We used a multidisciplinary approach comprised of botanical, anthracological and archaeobotanical investigations to compare P. elata patches with surrounding stands of mixed forest vegetation (“out-zones”). Charcoal samples were found in both zones, but were significantly more abundant in the soils of patches. Eleven groups of taxa were identified from the charcoals, most of them also present in the current vegetation. Potsherds were detected only inside P. elata patches and at different soil depths, suggesting a long human presence from at least 2150 to 195 BP, as revealed by our charcoal radiocarbon dating. We conclude that current P. elata patches most likely result from shifting cultivation that occurred ca. two centuries ago. The implications of our findings for the dynamics and management of light-demanding tree species are discussed. [less ▲]

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See detailHOW MANY HIPPOS (HOMHIP): Algorithm for automatic counts of animals with infra-red thermal imagery from UAV
Lhoest, Simon ULg; Linchant, Julie ULg; Quevauvillers, Samuel ULg et al

in International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences (2015), XL-3/W3

The common hippopotamus (Hippopotamus amphibius L.) is part of the animal species endangered because of multiple human pressures. Monitoring of species for conservation is then essential, and the ... [more ▼]

The common hippopotamus (Hippopotamus amphibius L.) is part of the animal species endangered because of multiple human pressures. Monitoring of species for conservation is then essential, and the development of census protocols has to be chased. UAV technology is considering as one of the new perspectives for wildlife survey. Indeed, this technique has many advantages but its main drawback is the generation of a huge amount of data to handle. This study aims at developing an algorithm for automatic count of hippos, by exploiting thermal infrared aerial images acquired from UAV. This attempt is the first known for automatic detection of this species. Images taken at several flight heights can be used as inputs of the algorithm, ranging from 38 to 155 meters above ground level. A Graphical User Interface has been created in order to facilitate the use of the application. Three categories of animals have been defined following their position in water. The mean error of automatic counts compared with manual delineations is +2.3% and shows that the estimation is unbiased. Those results show great perspectives for the use of the algorithm in populations monitoring after some technical improvements and the elaboration of statistically robust inventories protocols. [less ▲]

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See detailWIMUAS: Developing a tool to review wildlife data from various UAS flight plans
Linchant, Julie ULg; Lhoest, Simon ULg; Quevauvillers, Samuel ULg et al

in International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences (2015), XL-3/W3

To get around UAS limitations and propose a viable solution for wildlife monitoring, the development of new inventory methods is needed. However, most authors use the classic systematic transect method as ... [more ▼]

To get around UAS limitations and propose a viable solution for wildlife monitoring, the development of new inventory methods is needed. However, most authors use the classic systematic transect method as data processing and statistics are easier. We thus created an application to process data from every type of flight plan and to help detect and compare observations on large datasets. WiMUAS is a small software compatible with the open-source QGIS© that allows the creation of visual maps compatible with geographical information systems based on telemetry data and payload parameters to estimate the covered area. The application also has a slider for animal detection that allows multiple observers to record and compare their results for accurate counts. We then tested it on data from a trial realized on savannah animal populations in Democratic Republic of Congo using the Falcon UAS. We created a new type of flight plan, a rosette-shaped design that can be covered in three flights,.and repeated it twice. More than 5000 images were collected during the six flights. Image projection gives an area of 12,4 km2 for the first trial and of 12,1 km2 for the second. The mean sampling rate for both test is 6,1 %. Observers spotted buffaloes, hippos, warthogs and various antelopes with different success over an average rate of 8 images reviewed per minute. Resulting densities observed by the three observers are similar for each test (coefficient of variation 6,9 and 8,6 % respectively) but mean densities vary a lot between the two trials (23,8 and 6,5 animals/km2 respectively). [less ▲]

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See detailHow Many Hippos (HOMHIP): Algorithm for automatic counts of animals with infrared thermal imagery from UAV
Lhoest, Simon ULg; Linchant, Julie ULg; Quevauvillers, Samuel ULg et al

in International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences (2015), XL-3/W3

The common hippopotamus (Hippopotamus amphibius L.) is part of the animal species endangered because of multiple human pressures. Monitoring of species for conservation is then essential, and the ... [more ▼]

The common hippopotamus (Hippopotamus amphibius L.) is part of the animal species endangered because of multiple human pressures. Monitoring of species for conservation is then essential, and the development of census protocols has to be chased. UAV technology is considering as one of the new perspectives for wildlife survey. Indeed, this technique has many advantages but its main drawback is the generation of a huge amount of data to handle. This study aims at developing an algorithm for automatic count of hippos, by exploiting thermal infrared aerial images acquired from UAV. This attempt is the first known for automatic detection of this species. Images taken at several flight heights can be used as inputs of the algorithm, ranging from 38 to 155 meters above ground level. A Graphical User Interface has been created in order to facilitate the use of the application. Three categories of animals have been defined following their position in water. The mean error of automatic counts compared with manual delineations is +2.3% and shows that the estimation is unbiased. Those results show great perspectives for the use of the algorithm in populations monitoring after some technical improvements and the elaboration of statistically robust inventories protocols. [less ▲]

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See detailWIMUAS: A TOOL TO REVIEW WILDLIFE DATA FROM VARIOUS FLIGHT PLANS
Linchant, Julie ULg; Lhoest, Simon ULg; Quevauvillers, Samuel ULg et al

in International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences (2015), XL-3/W3

To get around UAS limitations and propose a viable solution for wildlife monitoring, the development of new inventory methods is needed. However, most authors use the classic systematic transect method as ... [more ▼]

To get around UAS limitations and propose a viable solution for wildlife monitoring, the development of new inventory methods is needed. However, most authors use the classic systematic transect method as data processing and statistics are easier. We thus created an application to process data from every type of flight plan and to help detect and compare observations on large datasets. WiMUAS is a small software compatible with the open-source QGIS© that allows the creation of visual maps compatible with geographical information systems based on telemetry data and payload parameters to estimate the covered area. The application also has a slider for animal detection that allows multiple observers to record and compare their results for accurate counts. We then tested it on data from a trial realized on savannah animal populations in Democratic Republic of Congo using the Falcon UAS. We created a new type of flight plan, a rosette-shaped design that can be covered in three flights,.and repeated it twice. More than 5000 images were collected during the six flights. Image projection gives an area of 12,4 km2 for the first trial and of 12,1 km2 for the second. The mean sampling rate for both test is 6,1 %. Observers spotted buffaloes, hippos, warthogs and various antelopes with different success over an average rate of 8 images reviewed per minute. Resulting densities observed by the three observers are similar for each test (coefficient of variation 6,9 and 8,6 % respectively) but mean densities vary a lot between the two trials (23,8 and 6,5 animals/km2 respectively). [less ▲]

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See detailCanopy Gap Mapping from Airborne Laser Scanning: An Assessment of the Positional and Geometrical Accuracy
Bonnet, Stéphanie ULg; Gaulton, Rachel; Lehaire, François et al

in Remote Sensing (2015), 7

Canopy gaps are small-scale openings in forest canopies which offer suitable micro-climatic conditions for tree regeneration. Field mapping of gaps is complex and time-consuming. Several studies have used ... [more ▼]

Canopy gaps are small-scale openings in forest canopies which offer suitable micro-climatic conditions for tree regeneration. Field mapping of gaps is complex and time-consuming. Several studies have used Canopy Height Models (CHM) derived from airborne laser scanning (ALS) to delineate gaps but limited accuracy assessment has been carried out, especially regarding the gap geometry. In this study, we investigate three mapping methods based on raster layers produced from ALS leaf-off and leaf-on datasets: thresholding, per-pixel and per-object supervised classifications with Random Forest. In addition to the CHM, other metrics related to the canopy porosity are tested. The gap detection is good, with a global accuracy up to 82% and consumer’s accuracy often exceeding 90%. The Geometric Accuracy (GAc) was analyzed with the gap area, main orientation, gap shape-complexity index and a quantitative assessment index of the matching with reference gaps polygons. The GAc assessment shows difficulties in identifying a method which properly delineates gaps. The performance of CHM-based thresholding was exceeded by that of other methods, especially thresholding of canopy porosity rasters and the per-pixel supervised classification. Beyond assessing the methods performance, we argue the critical need for future ALS-based gap studies to consider the geometric accuracy of results. [less ▲]

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See detailForEstimator : un nouvel outil cartographique pour mieux connaître la forêt wallonne
Dedry, Laurent ULg; De Thier, Olivier ULg; Perin, Jérôme ULg et al

in Forêt-Nature (2015), (135), 40-46

Suite à l’acquisition par le Service public de Wallonie d’une couverture LiDAR de l’ensemble du territoire régional, et à l’établissement d’un modèle numérique de hauteur basé sur cette dernière, Gembloux ... [more ▼]

Suite à l’acquisition par le Service public de Wallonie d’une couverture LiDAR de l’ensemble du territoire régional, et à l’établissement d’un modèle numérique de hauteur basé sur cette dernière, Gembloux Agro-BioTech (GxABt) a mis au point un plugin QGIS, baptisé «ForEstimator», permettant aux gestionnaires et propriétaires forestiers de calculer facilement la hauteur dominante de leurs peuplements d’épicéas et de douglas équiennes. De plus, pour corriger l’ancienneté des données LiDAR, le plugin est couplé à un modèle de prédiction de la croissance de la hauteur dominante. Cette originalité permet d’actualiser l’estimation à une date postérieure à l’acquisition des données LiDAR. Parallèlement, l’équipe de GxABT a pu déterminer l’arbre le plus haut de Wallonie. Il s’agit d’un douglas de 61 mètres de haut au sein d’un peuplement mélangé de douglas et tsuga, planté en 1900, situé à Bouillon. ForEstimator permet aux gestionnaires forestiers de produire facilement des cartes de hauteur dominante, de productivité des peuplements, etc. [less ▲]

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See detailAgent-based modelling of the spatial pattern of leisure visitation in forests: A case study in Wallonia, south Belgium
Li, Sen; Colson, Vincent; Lejeune, Philippe ULg et al

in Environmental Modelling & Software (2015), 71

The leisure use of forests is a fast growing sector in European tourism. The difficulties in monitoring real usage pattern have hindered communications in tourism, conservation and public health in ... [more ▼]

The leisure use of forests is a fast growing sector in European tourism. The difficulties in monitoring real usage pattern have hindered communications in tourism, conservation and public health in forested areas. In this study, we present an agent-based model to approximate forest visit patterns at the regional level, based on the visitor, residential and forest attributes. The model was then adapted locally for Wallonia, south Belgium, to predict the daily distribution of forest visits and visitor flows. The results suggest high visit rates in urban forests. In highly attractive forests that are distant from major cities, the visit rates may greatly respond to the visitor-level and environmental changes. Future empirical investigations are encouraged to build a cross-contextual understanding on visitors' decision-making mechanisms and to identify how these mechanisms may be influenced by environmental factors operating at different spatio-temporal levels. [less ▲]

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See detailNew technologies in conservation: monitoring African wildlife with UAS
Linchant, Julie ULg; Semeki, Jean; Lejeune, Philippe ULg et al

Conference (2014, December 13)

In the vast protected areas of Africa, traditional wildlife surveys performed by plane or foot are logistically difficult to implement due to the lack of means and appropriate materials. Moreover, the ... [more ▼]

In the vast protected areas of Africa, traditional wildlife surveys performed by plane or foot are logistically difficult to implement due to the lack of means and appropriate materials. Moreover, the possibilities of encountering poachers in the field pose a serious risk to the monitoring teams. Over the last decade, civilian UAS (Unmanned Aerial Systems) boomed in natural resource monitoring. One of the biggest challenges of the UAS is to replace traditional wildlife censuses for the application of wildlife conservation. Parameters have to be approached in a different way than before. We performed test flights in the open savannah of the Garamba National Park during the wet season using the Falcon Unmanned UAS. Both photos (Sony Nex7, 24Mp) and videos, including thermal infrared videos (Tamarisk 640x480), have been used. Flight altitude ranged from 50 to 200m and pictures showed that animals can be effectively detected at 100m. We spotted elephants, hippopotamus and buffaloes as well as other smaller species such as hartebeests, kobs and warthogs. Thermal videos gave medium quality results during the day due to the heat but performed well during the night. The limited range and endurance of the UAS suggest a rethink of the usual census protocols. We therefore tested new flight plans in a rosette shape to take advantage of the higher points in the park, with transects having the length of the maximal range. Twelve transects of 10km can be covered in half a day with pictures covering a 15.6km² area. Human activities could also be detected. Pictures showed areas burned by poachers and the thermal infrared camera allows the detection of fires from a high altitude. Future developments need to be investigated such as automatic detection to review the huge amount of data collected and statistical methods must be adapted to those challenging situations. [less ▲]

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See detailForest inventory with Terrestrial LiDAR: what about Hand-Held Mobile LiDAR?
Bauwens, Sébastien ULg; Bartholomeus, Harm; Piboule, Alexandre et al

Conference (2014, November 05)

For a decade, studies of the application of static Terrestrial Laser Scanner (TLS) in plotwise forest inventories are giving more and more effective results. In spite of the improvements occurring in ... [more ▼]

For a decade, studies of the application of static Terrestrial Laser Scanner (TLS) in plotwise forest inventories are giving more and more effective results. In spite of the improvements occurring in processing scan data to extract forest attributes, the occlusion effect is still limiting the processing efficiency. A multi-scan approach is recommended to reduce this effect. However, such approach needs pre-scan preparations (setting up the plot, targets positioning), it requires data registration and it comes at a higher data collection cost. In this study we explore the potential of a Hand-held mobile LiDAR System (HMLS) as new LiDAR tool to scan forest plots. HMLS data are compared to static TLS data (single and multi-scan) in terms of data acquisition, registration time and quality of automatic DBH extraction. The low weight, small size of the instrument and no targets requirements reduce the time of pre-scan preparations to the time needed for single scan which is 6 times less than scanning a plot with 5 scans. The registration time depends of the time spent to scan the plot and it is of the same magnitude than single scan. The resulting point cloud of the HMLS is noisier than TLS point clouds. Nevertheless, error on DBH estimations is similar to scanning a plot with a TLS positioned at 5 locations. RMSE is higher than multi-scan and close to single scan for trees detected by the both LiDAR technologies. This first study exhibits the high potential of HMLS by its simple use, which needs only one operator while presenting similar results in automatic DBH extraction than static TLS. Technology and registering method improvements of this type of mobile LiDAR will reduce the noise of the point cloud, which might reduce the DBH RMSE. [less ▲]

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See detailHow to survey your hippos night and day? Follow them in bed with drones!
Linchant, Julie ULg; Lejeune, Philippe ULg; Vermeulen, Cédric ULg

Scientific conference (2014, October 20)

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See detailSeasonal variations of wild boar Sus scrofa distribution in agricultural landscapes: a species distribution modelling approach
Morelle, Kevin ULg; Lejeune, Philippe ULg

in European Journal of Wildlife Research (2014)

Seasonal changes in the distribution of animals can have an important impact on the ecosystem. In agricultural landscapes, the seasonal movement of the wild boar Sus scrofa towards field crops often ... [more ▼]

Seasonal changes in the distribution of animals can have an important impact on the ecosystem. In agricultural landscapes, the seasonal movement of the wild boar Sus scrofa towards field crops often results in damages and makes control of the population difficult. The plasticity of the species to cope with different habitats is largely proven, but the environmental and human drivers of this seasonal habitat shift at the population scale remain largely unknown. Using MaxEnt and two seasonally distinct presence datasets, we contrasted the distribution of wild boar in southern Belgium during the growing and hunting seasons to (i) analyse seasonal drivers of the distribution and (ii) forecast the potential spread of the species north to its current distribution. We demonstrated that during the growing season, wild boar range almost double, owing to the cover and food provided by agricultural areas, thereby enhancing the movement and spread of the species. We found that the seasonal distribution of wild boar in agricultural lands is mostly influenced by the search for cover and food provided alternatively by forest and field crops. Interestingly, it seems that this search for cover operates under the constraint of a threshold distance. Our results indeed reveal an increased probability of presence not only in the vicinity of forests but also above a threshold distance of 865 m from the forest edge, suggesting that wild boar can overcome the dependence to forest cover. The forecast distribution of wild boar highlighted a potential increase of the current range into suitable habitat between 63 and 168 km2. To counteract the potential spread of the species into agricultural habitats and the consecutive damages, we insist on the need for the development of integrated management strategies, combining land use spatial configuration and wild boar spatial behaviour. [less ▲]

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