Astrid Verhegghen

National forest cover change in Congo Basin: deforestation, reforestation, degradation and regeneration for the years 1990, 2000 and 2005

This research refers to an object-based automatic method combined with a national expert validation to produce regional and national forest cover change statistics over Congo Basin. A total of 547 sampling sites systematically distributed over the whole humid forest domain are required to cover the six Central African countries containing tropical moist forest. High resolution imagery is used to accurately estimate not only deforestation and reforestation but also degradation and regeneration. The overall method consists of four steps: (i) image automatic preprocessing and preinterpretation, (ii) interpretation by national expert, (iii) statistic computation and (iv) accuracy assessment. The annual rate of net deforestation in Congo Basin is estimated to 0.09% between 1990 and 2000 and of net degradation to 0.05%. Between 2000 and 2005, this unique exercise estimates annual net deforestation to 0.17% and annual net degradation to 0.09%. An accuracy assessment reveals that 92.7% of tree cover (TC) classes agree with independent expert interpretation. In the discussion, we underline the direct causes and the drivers of deforestation. Population density, small-scale agriculture, fuelwood collection and forests accessibility are closely linked to deforestation, whereas timber extraction has no major impact on the reduction in the canopy cover. The analysis also shows the efficiency of protected areas to reduce deforestation. These results are expected to contribute to the discussion on the reduction in CO2 emissions from deforestation and forest degradation (REDD+) and serve as reference for the period.

The Potential of Sentinel Satellites for Burnt Area Mapping and Monitoring in the Congo Basin Forests

In this study, the recently launched Sentinel-2 (S2) optical satellite and the active radar Sentinel-1 (S1) satellite supported by active fire data from the MODIS sensor were used to detect and monitor forest fires in the Congo Basin. In the context of a very strong El Nino event, an unprecedented outbreak of fires was observed during the first months of 2016 in open forests formations in the north of the Republic of Congo. The anomalies of the recent fires and meteorological situation compared to historical data show the severity of the drought. Burnt areas mapped by the S1 SAR and S2 Multi Spectral Instrument (MSI) sensors highlight that the fires occurred mainly in Marantaceae forests, characterized by open tree canopy cover and an extensive tall herbaceous layer. The maps show that the origin of the fires correlates with accessibility to the forest, suggesting an anthropogenic origin. The combined use of the two independent and fundamentally different satellite systems of S2 and S1 captured an extent of 36,000 ha of burnt areas, with each sensor compensating for the weakness (cloud perturbations for S2, and sensitivity to ground moisture for S1) of the other.

A global NDVI and EVI reference data set for land-surface phenology using 13 years of daily SPOT-VEGETATION observations

Time series of vegetation indices (VIs) obtained by remote sensing are widely used to study phenology on regional and global scales. The aim of the study is to design a method and to produce a reference data set describing the seasonal and inter-annual variability of the land-surface phenology on a global scale. Specific constraints are inherent in the design of such a global reference data set: (1) the high diversity of vegetation types and the heterogeneous conditions of observation, (2) a near-daily resolution is needed to follow the rapid changes in phenology, (3) the time series used to depict the baseline vegetation cycle must be long enough to be representative of the current vegetation dynamic and encompass anomalies, and (4) a spatial resolution consistent with a land-cover-specific analysis should be privileged. This study focuses on the SPOT (Satellite Pour l’Observation de la Terre)-VEGETATION sensor and its 13-year time series of reflectance values. Five steps addressing the noise and the missing data in the reflectance time series were selected to process the daily multispectral reflectance observations. The final product provides, for every pixel, three profiles for 52 × 7-day periods: a mean, a median, and a standard deviation profile. The mean and median profiles represent the reference seasonal pattern for variation of the vegetation at a specific location whereas the standard deviation profile expresses the inter-annual variability of VIs. A quality flag at the pixel level demonstrated that the reference data set can be considered as a reliable representation of the vegetation phenology in most parts of the Earth.

Cartographie du couvert forestier et des changements du couvert forestier en Afrique centrale

Le rôLe de La faune dans Le cadre de La sécurité aLimentaire en afrique centraLe : une menace pour La biodiversité ?Au cours des vingt dernières années, les six pays forestiers du bassin du Congo ont conçu et adopté des politiques forestières dans le but, d’une part, de réduire la pauvreté notamment en milieu rural et, d’autre part, de contribuer à l’amélioration de leurs économies nationales et de promouvoir la gestion responsable de la diversité biologique. En effet, dans la région, la gestion des forêts intervient dans un contexte de pauvreté rurale généralisée : on estime que plus de 58 % de ces populations vivent en dessous du seuil de pauvreté (avec 2

Review and Combination of Recent Remote Sensing Based Products for Forest Cover Change Assessments in Cameroon

/jour), la majorité d’entre elles habitant dans des zones où la forêt tient une place prédominante (World Bank, 2010). Au fil des années, les nouvelles lois ont permis d’améliorer considérablement les méthodes de gestion des forêts. On a constaté une forte augmentation du nombre de concessions forestières gérées au moyen de plans d’aménagement forestier et, surtout, un accroissement des impôts collectés par le Trésor public (Eba’a Atyi et al., 2009). Cependant, la grande majorité de ces réformes politiques se sont concentrées sur les activités forestières industrielles et orientées vers l’exportation, en négligeant la production par sciage artisanal, à plus petite échelle et vendue en grande partie sur les marchés intérieurs et régionaux. Les titres d’exploitation à petite échelle qui autorisent les citoyens à abattre un nombre limité d’arbres, généralement pour leurs besoins personnels et à des fins non commerciales, sont en effet inclus dans tous les cadres légaux de la région. Cependant, ils ne sont pas adaptés aux besoins actuels des scieurs artisanaux et, à ce titre, ils sont rarement sollicités. Par conséquent, le secteur domestique du bois reste en grande partie informel en dépit de son importance. Ses impacts économiques, écologiques et sociaux sont méconnus des ministères et ne sont pas pris en compte dans les statistiques nationales et internationales. Par exemple, pour l’année 2007, les statistiques officielles faisaient état d’une production de bois en Afrique centrale d’environ 8,4 millions de m3 (Eba’a Atyi et al., 2009), le Gabon et le Cameroun étant les plus gros producteurs et la République démocratique du Congo (RDC) le plus petit d’entre eux. Cependant, l’ensemble des données nationales et internationales, notamment celles de la FAOSTAT, de l’UN Comtrade22 ou de l’OIBT, ne concernaient que la production du secteur forestier industriel et orienté vers l’exportation.

Assessing forest degradation from selective logging using time series of fine spatial resolution imagery in Republic of Congo

SUMMARY Two recent remote sensing derived products providing assessment of forest cover change in the Congo Basin for the last two decades were compared and combined to obtain estimates of forest cover change in Cameroon for the period 1990–2012. The intensity of deforestation in the whole region decreased from the 1990s to the 2000s. Forest loss is observed everywhere in Cameroon but present higher intensity nearby the Atlantic coast. The analysis of the spatial distribution of the forest loss in Cameroon reveals that an important part of the loss is happening outside the permanent and the non-permanent forest domain. The Landsat spatial resolution used in the two products allows us to capture change caused by agro-industrial exploitation as well as shifting cultivation, infrastructure and selective logging when the area affected is large enough. But it fails to monitor forest degradation and small scale deforestation events.

Statistics of TanDEM-X DSM, coherence and backscatter for the characterization of tropical forest structural configuration

Time series of SPOT4Take5 and RapidEye acquired in the period from February to June 2013 are used to monitor the dynamic of logging-related disturbances in the forest cover of a selective logging concession situated in the North of the Republic of Congo. First results of the time series analysis highlights the very rapid changes in the forest cover, as most logging gaps are totally disappearing in the space of a few months.

Mapping Congo Basin vegetation types from 300 m and 1 km multi-sensor time series for carbon stocks and forest areas estimation

Orbital InSAR is an ideal observation instrument in tropical areas, where optical imagery is hampered by persistent cloud cover. In particular, TanDEM-X provides backscatter, interferometric coherence and digital surface model from phase (DSM) at high spatial resolution (4 m), whose spatial statistics can in principle hold information on forest structure. This information, in turn, could lay the ground to distinguish between naturally occurring forest heterogeneity (e.g. due to the presence of emergent species) and forest disturbance, such as forest degradation (e.g. removal of vegetation) and forest regeneration. The present work investigates by experimental analysis how statistical measures of the spatial random fields (SRF) provided by TanDEM-X InSAR data can be mapped onto properties of the forest spatial structure. The analysis is focused on a case study in the Republic of Congo.