Flore, structure et état sanitaire des peuplements ligneux des parcs agroforestiers des forêts de Dindéresso et de Kuinima à l’ouest du Burkina Faso

Les parcs agroforestiers occupent des superficies non négligeables au Burkina Faso. Mais, du fait de la pression foncière, ils subissent des formes d’exploitation qui menacent leur existence dans le moyen terme. Pour une gestion durable des parcs agroforestiers, leur connaissance sur le plan floristique s’impose. C’est ainsi qu’une étude floristique a été menée dans les parcs agroforestiers des forêts classées de Dindéresso et de Kuinima à l’Ouest du Burkina Faso. L’objectif est de contribuer à une meilleure gestion du peuplement ligneux des parcs agroforestiers. Pour ce faire, un inventaire forestier dans des placettes circulaires de 900 m² a été réalisé en vue d’établir la liste floristique, la diversité spécifique et d’apprécier l’état de la régénération et l’état sanitaire des peuplements ligneux. Au total, 27 espèces ligneuses réparties en 14 familles et 27 genres dans les parcs agroforestiers de Dindéresso et 27 espèces ligneuses réparties en 12 familles et 26 genres dans les parcs agroforestiers de Kuinima ont été inventoriées. La diversité spécifique de Shannon-Weaver est faible avec 1,80 bit pour les parcs agroforestiers de Dindéresso et 1,33 bit pour ceux de Kuinima. La régénération est beaucoup plus marquée par l’espèce Vitellaria paradoxa Gaertn.f. suivie de Anacardium occidentaleL. [cult.]. Les taux de régénération sont de l’ordre de 54,12% et 9,41% pour Dindéresso puis 35,64% et 26,60% pour Kuinima respectivement, pour Vitellaria paradoxa et Anacardium occidentale. L’appréciation de l’état sanitaire révèle que 49,85% des pieds de Vitellaria paradoxa inventoriés dans la forêt classée de Kuinima sont parasités. Par contre dans la forêt classée de Dindéresso, le taux de parasitisme des pieds de Vitellaria paradoxa est de 13,37%. Au regard de ces taux de parasitisme, il est plus que nécessaire de développer des stratégies de lutte contre ces plantes parasites. À court et moyen termes si rien n’est fait, ces parasites affecteront considérablement les capacités de cette espèce agroforestière à fournir des biens et services. Agroforestry parks occupy significant areas in Burkina Faso. But, due to land pressure, they are subjected to forms of exploitation which threaten their existence in the medium term. For a sustainable management of agroforestry parks, their flora knowledge is essential. Thus, a floristic study was carried out in the agroforestry parks of the classified forests of Dindéresso and Kuinima in western Burkina Faso. The objective is to contribute to better management of the woody settlement in agroforestry parks. So, a forest inventory in circular plots of 900 m² was carried out in order to establish the floristic list, the specific diversity and to assess the state of regeneration and the state of health of the woody settlement. A total of 27 woody species divided into 14 families and 27 genera in the agroforestry parks of Dindéresso and 27 woody species divided into 12 families and 26 genera in the agroforestry parks of Kuinima were inventoried. The specific diversity of Shannon-Weaver is low with 1.80 bit for the agroforestry parks of Dinderesso and 1.33 bit for those of Kuinima. Regeneration is much more marked by the species Vitellaria paradoxa Gaertn. f. followed by Anacardium occidentale L. [cult.]. The regeneration rates are of the order of 54.12% and 9.41% for Dindéresso, then 35.64% and 26.60% for Kuinima, respectively for Vitellaria paradoxa and Anacardium occidentale. The assessment of the health status reveals that 49.85% of Vitellaria paradoxa plants inventoried in the Kuinima classified forest are parasitized. On the other hand in the classified forest of Dindéresso, the rate of parasitism of the feet of Vitellaria paradoxa is 13.37%. In view of these parasitism rates, it is more than necessary to develop strategies to combat these parasitic plants. In the short to medium term, if left unchecked, these pests will significantly affect the ability of this agroforestry species to provide goods and services

Dynamique spatio-temporelle des savanes boisées de la forêt classée de Tiogo au Burkina Faso

Les aires protégées du Burkina Faso connaissent un phénomène d'anthropisation accrue. A cela s'ajoute l'effet des changements climatiques. Ainsi, ces facteurs ont des conséquences dont la baisse de la biodiversité. Cette étude a pour objectif principal d’analyser de la dynamique spatio-temporelle des savanes boisées. Elle a été conduite dans la forêt classée de Tiogo. Des images Landsat TM de 1986 et ETM de 2010 ont été utilisées. Deux cartes d’occupation du sol, respectivement de 1986 et de 2010 ont été réalisées avec trois classes thématiques. De ces deux cartes d’occupation du sol, deux cartes de répartition spatiale des savanes boisées de 1986 et 2010 ont été générées. Les résultats cartographiques révèlent une forte régression des savanes boisées passant de 35,17% en 1986 à 18,04% en 2010. Durant la même période, les zones d’anthropisation ont progressé d’environ 4,38% par an. L’analyse de la dynamique spatiale a montré une fragmentation des savanes boisées entre 1986 et 2010. Cette fragmentation est principalement due à des activités anthropiques, notamment l’exploitation forestière et les défrichements agricoles. Ceci constitue donc une menace croissante pour la conservation de la biodiversité dans cette forêt classée si aucune mesure n’est prise pour inverser les tendances.© 2015 International Formulae Group. All rights reserved.Mots clés: Aires protégées, savanes, fragmentation, anthropisation, imagerie satellitaire, Afrique de l’OuestEnglish AbstractThis study is a contribution to the analysis of the spatio-temporal dynamics of the savanna within protected areas. It was conducted in the classified forest of Tiogo in Central West of Burkina Faso. Images 1986 Landsat TM and ETM of 2010 have been used. Two land use maps of 1986 and 2010 respectively, were made with respect to three thematic classes defined. From these two land use maps, two maps of spatial distribution of woody savanna of 1986 and 2010 were generated. The mapping results reveal a sharp decline of woody savanna, declining from 35.17% in 1986 to 18.04% in 2010. During the same period, anthropization areas have increased of approximately 4.38% per year. Analysis of the spatial dynamics has shown fragmentation of savanna between 1986 and 2010. This fragmentation is due to anthropogenic activities, including logging and agricultural clearing. This is therefore a growing threat to the conservation of biodiversity in this classified forest if no action is taken to reverse the trends.© 2015 International Formulae Group. All rights reserved.Keywords: Protected areas, savannas, fragmentation, anthropization, satellite imagery, West Afric

Predicting vegetation dynamics in Deux Balé National Park, Burkina Faso, using land change modeler

In recent years, the natural vegetation of Burkina Faso has undergone unprecedented anthropisation. To date, most studies have focused only on diachronic analysis based on satellite imagery. Land use dynamics studies give an account of the past and present situation, but do not provide quantitative and qualitative information on the future of this vegetation. On the other hand, a prospective analysis of the dynamics would enable us to better assess the future of our forest ecosystems. Predictive data are essential for decision-making and implementing appropriate policy responses relating to sustainable forest resources management. The main objective of this study was to predict the vegetation dynamics of the Deux Balé National Park by modelling the year 2025. Thus, we selected the variables that best explained the anthropization process. A land change model was selected for the study. The model was calibrated using only variables with a V-Cramer coefficient greater than or equal to 0.1. This model is based on error budgeting and prediction. Visual and statistical comparisons of the simulated and actual 2016 maps allowed for better calibration of the model to simulate changes in the area of land-cover classes by 2025. The results revealed that, between 2016 and 2025, a significant regression of savanna vegetation will occur in favor of anthropized areas and gallery forests. Thus, from this period, gallery forests and anthropized areas covered up to 138 ha and 2914 ha, respectively. However, the savanna vegetation area decreased by 1186 ha, 961 ha, and 893 ha from 2016 to 2025, respectively. Therefore, urgent action must be taken to preserve the potential of the forest resources in parks

Mapping Tree Canopy Cover and Aboveground Biomass in Sudano-Sahelian Woodlands Using Landsat 8 and Random Forest

Accurate and timely maps of tree cover attributes are important tools for environmental research and natural resource management. We evaluate the utility of Landsat 8 for mapping tree canopy cover (TCC) and aboveground biomass (AGB) in a woodland landscape in Burkina Faso. Field data and WorldView-2 imagery were used to assemble the reference dataset. Spectral, texture, and phenology predictor variables were extracted from Landsat 8 imagery and used as input to Random Forest (RF) models. RF models based on multi-temporal and single date imagery were compared to determine the influence of phenology predictor variables. The effect of reducing the number of predictor variables on the RF predictions was also investigated. The model error was assessed using 10-fold cross  validation. The most accurate models were created using multi-temporal imagery and variable selection, for both TCC (five predictor variables) and AGB (four predictor variables). The coefficient of determination of predicted versus observed values was 0.77 for TCC (RMSE = 8.9%) and 0.57 for AGB (RMSE = 17.6 tons∙ha−1). This mapping approach is based on freely available Landsat 8 data and relatively simple analytical methods, and is therefore applicable in woodland areas where sufficient reference data are available. Funding text: Swedish International Development Cooperation Agency (Sida); Swedish Energy Agency; Swedish Research Council (VR/Sida)</p

Spatio-Temporal Evolution of Rainfall over the Period 1981–2020 and Management of Surface Water Resources in the Nakanbe–Wayen Watershed in Burkina Faso

Spatio-temporal analysis of rainfall trends in a watershed is an effective tool for sustainable water resources management, as it allows for an understanding of the impacts of these changes at the watershed scale. The objective of the present study is to analyze the impacts of climate change on the availability of surface water resources in the Nakanbe–Wayen watershed over the period from 1981 to 2020. The analysis was conducted on in situ rainfall data collected from 14 meteorological stations distributed throughout the watershed and completed with CHIRPS data. Ten precipitation indices, recommended by the ETCCDI (Expert Team on Climate Change Detection and Indices), were calculated using the RClimDex package. The results show changes in the distribution of annual precipitation and an increasing trend in annual precipitation. At the same time, a trend towards an increase in the occurrence and intensity of extreme events was also observed over the last 4 decades. In light of these analyses, it should be emphasized that the increase in precipitation observed in the Nakanbe–Wayen watershed is induced by the increase in the occurrence and intensity of events, as a trend towards an increase in persistent drought periods (CDD) is observed. This indicates that the watershed is suffering from water scarcity. Water stress and water-related hazards have a major impact on communities and ecosystems. In these conditions of vulnerability, the development of risk-management strategies related to water resources is necessary, especially at the local scale. This should be formulated in light of observed and projected climate extremes in order to propose an appropriate and anticipated management strategy for climate risks related to water resources at the watershed scale

Mapping Tree Height in Burkina Faso Parklands with TanDEM-X

Mapping of tree height is of great importance for management, planning, and research related to agroforestry parklands in Africa. In this paper, we investigate the potential of spotlight-mode data from the interferometric synthetic aperture radar (InSAR) satellite system TanDEM-X (TDM) for mapping of tree height in Sapone, Burkina Faso, a test site characterised by a low average canopy cover (similar to 15%) and a mean tree height of 9.0 m. Seven TDM acquisitions from January-April 2018 are used jointly to create high-resolution (similar to 3 m) maps of interferometric phase height and mean canopy elevation, the latter derived using a new, model-based processing approach compensating for some effects of the side-looking geometry of SAR. Compared with phase height, mean canopy elevation provides a more accurate representation of tree height variations, a better tree positioning accuracy, and better tree height estimation performance when assessed using 915 trees inventoried in situ and representing 15 different species/genera. We observe and discuss two bias effects, and we use empirical models to compensate for these effects. The best-performing model using only TDM data provides tree height estimates with a standard error (SE) of 2.8 m (31% of the average height) and a correlation coefficient of 75%. The estimation performance is further improved when TDM height data are combined with in situ measurements; this is a promising result in view of future synergies with other remote sensing techniques or ground measurement-supported monitoring of well-known trees.Funding Agencies|Swedish National Space Agency [112/16]</p