Hugues Claessens

Site index curves and autecology of ash, sycamore and cherry in Wallonia (Southern Belgium)

Summary The work described in this article forms part of an exploratory study 1 whose aim was to determine the main aspects of the autecology of ash (Fraxinus excelsior L.), sycamore (Acer pseudoplatanus L.) and cherry (Prunus avium L.) in Wallonia (Southern Belgium). The potential productivity of these species was studied using the site index approach (the height a crop achieves at a given age) which is the most widely accepted means for estimating site quality. As a first step, a set of site index curves were constructed from stem analysis and semi-permanent plots data using the Johnson (1935) and Schumacher (1939) model for ash and the Duplat and Tran-Ha (1986) model II for sycamore and cherry. For ash, dominant height achieved at age 50 is related to various soil-site characters (through adequate multiple regression analysis) in order to make the predictions of site quality applicable to both forested and non-forested land. Furthermore the sites expressed through soil attributes are classified in ‘a site catalogue’ for each species according to their productivity level.

Discrimination of Deciduous Tree Species from Time Series of Unmanned Aerial System Imagery

Technology advances can revolutionize Precision Forestry by providing accurate and fine forest information at tree level. This paper addresses the question of how and particularly when Unmanned Aerial System (UAS) should be used in order to efficiently discriminate deciduous tree species. The goal of this research is to determine when is the best time window to achieve an optimal species discrimination. A time series of high resolution UAS imagery was collected to cover the growing season from leaf flush to leaf fall. Full benefit was taken of the temporal resolution of UAS acquisition, one of the most promising features of small drones. The disparity in forest tree phenology is at the maximum during early spring and late autumn. But the phenology state that optimized the classification result is the one that minimizes the spectral variation within tree species groups and, at the same time, maximizes the phenologic differences between species. Sunlit tree crowns (5 deciduous species groups) were classified using a Random Forest approach for monotemporal, two-date and three-date combinations. The end of leaf flushing was the most efficient single-date time window. Multitemporal datasets definitely improve the overall classification accuracy. But single-date high resolution orthophotomosaics, acquired on optimal time-windows, result in a very good classification accuracy (overall out of bag error of 16%).

Characterization of riparian zones in wallonia (belgium) from local to regional scale using aerial lidar data and photogrammetric DSM

The present study proposes an innovative approach to automatically extract riparian zone characteristics in order to assess its quality, from pre-determined river management reaches (1-3 km long) to regional scale (ca. 13,000 km for 1,000 management sectors). The aim of this remotely sensed monitoring is to improve river and riparian zone management and planning by providing some key information for river managers. The methodology was developed based on two watersheds covering approximately 500 km of river network (ca. 200 management sectors). The riparian zone quality is evaluated through various indicators of its ecological integrity (e.g., longitudinal continuity of riparian forest, mean vegetation height and relative standard deviation), hydromorphological quality and physical settings (e.g., flow channel extent, floodplain width, channel sinuosity). The physical characteristics of the riparian zone are mainly extracted from a high quality Digital Terrain Model (derived from ALS data), while the attributes of the riparian forest are derived from a hybrid Canopy Height Model (photogrammetric Digital Surface Model - Lidar derived DTM). This first research is exclusively based on data which are available at the regional scale (170,000 km 2 ) to develop automated tools to implement the methodology to the whole Walloon river network (13,000 km) before 2015 with an update frequency of three years (photogrammetric DSM survey frequency). Moreover, our approach is based on a photogrammetric Digital Surface Model which is derived from raw images of an orthophoto coverage. As most European countries are regularly covered by orthophoto surveys, our approach is widely replicable in countries where a quality DTM is available.

La gestion patrimoniale des forêts anciennes de Wallonie (Belgique)

Thierry Kervyn1 | Jean-Pierre Scohy2 | Didier Marchal2 | Olivier Collette3 | Brieuc Hardy4 Laurence Delahaye1 | Lionel Wibail1 | Floriane Jacquemin5 | Marc Dufrêne5 | Hugues Claessens5 1 Département d’Étude du Milieu naturel et agricole (DGARNE, SPW) 2 Département de la Nature et des Forêts (DGARNE, SPW) 3 Département du Patrimoine (DGATLPE, SPW) 4 Earth and Life Institute (UCL) 5 Gembloux Agro-BioTech (ULiège)

Dosage de la lumière pour maintenir la coexistence d’espèces d’ombre et de demi-ombre dans la régénération de la futaie irrégulière

Le traitement en futaie irrégulière et mélangée, au couvert continu dont le renouvellement est assuré par la régénération naturelle (de Türckheim et Bruciamacchie, 2005), a de plus en plus d’adeptes. L’engouement pour ce traitement est tel qu’il a récemment été imposé dans certaines conditions en forêts publiques de Wallonie [circulaire “Pro Silva” imposée pour les forêts publiques de Wallonie (Sanchez, 2013)]. Néanmoins, cette sylviculture demande une bonne connaissance des processus naturels dont le sylviculteur essaye de tirer profit. L’une des principales difficultés réside certainement dans le maintien du mélange à partir de la régénération naturelle. En effet, si le peuplement n’est pas suffisamment ouvert, les semis des espèces tolérantes à l’ombre s’installent plus efficacement que les semis des espèces moins tolérantes à l’ombre. Peu à peu, les espèces les plus tolérantes à l’ombre dominent la composition du peuplement et compromettent ainsi l’objectif de maintien d’un cortège d’espèces compagnes diversifié. À l’inverse, si l’on ouvre fortement le peuplement, une vague de régénération dense et peu diversifiée s’installe souvent. Dominée par l’espèce la plus performante, et notamment celle qui a pu s’établir dans l’ombre, elle compromet également le maintien de la diversité spécifique et conduit à des travaux sylvicoles supplémentaires.