Monitoring a pioneer front using SPOT-VEGETATION time series

Since the 1960s, the Amazonian forest has been shrinking with the advance of primarily commercial cultivated areas. The pattern is being strengthened by high population growth and the migration of populations towards these newly deforested pioneer fronts. These trends are causing space to be appropriated to the detriment of forested areas. It has become essential to be able to locate areas on the pioneer front quickly and systematically in order to characterize new phases in advancing deforestation as they occur. However, satellite tools with high spatial resolution are not suited to monitoring of this type, as their temporal resolution is too broad and data processing is characteristically complex. Although low–resolution satellite images therefore seem more appropriate to these analyses, they can raise major problems when the target areas are very specific. In order to use imagery with low spatial resolution, such as SPOT-VEGETATION images, this study proposes a monitoring methodology based on a deforestation front of very small size. The method could be extrapolated to other deforestation fronts to investigate new areas to be monitored and thus establish diagnoses of the temporal dynamics of landscape transformation. (Résumé d'auteur

Effects of land use pattern on invasive plant diversity in Guinean savanna ecosystems of Togodo protected area, Togo

Tropical natural ecosystems host a very diverse flora and fauna and are key ecosystems for global climate and biogeochemical regulation. Unfortunately, in West African landscapes, large areas of savanna and forest have been progressively replaced or fragmented by crops. These dynamics promote the spread of many invasive plants representing on the one hand, a real and growing threat for many conservation areas and on the other hand, a serious problem for agricultural production. Similarly, Togodo Protected Area, a crucial habitat for many vulnerable and endangered species in Togo, is submitted to important threats by human disturbance which promote the establishment and development of invasive plants. The eradication of invasive plants already established over a large area is rarely possible. Thus, understanding and predicting the invasive success of plants is one of the major concerns of the ecology of invasive plants. In order to evaluate the relations between current land use patterns and invasive plant diversity and abundance, first, a typology of landscape elements was defined based on the heterogeneity of the environment (forests, savannas, fallows, oil palm and teak plantations, crops). Then, in each identified landscape element, the dominant plant species have been identified. A total of 133 botanical surveys including: 27 in crops, 41 in fallows, 17 in palm plantations, 13 in teak plantations, 18 in savannas and 17 in forests. As results, 178 dominant plant species including 31 (17.42 %) invasive or potentially invasive were recorded. In terms of diversity, fallows (25 species) and crops (15 species) contain more dominant invasive species, unlike teak plantations and forests dominated by only 4 and 5 species respectively. Among the most common dominant invasive species, Panicum maximum Jacq. and Chromolaena odorata (L.) R.M.King & H.Rob. dominate all types of landscape elements while other species such as Acmella oleracea (L.) R.K.Jansen and Triumfetta rhomboidea Jacq. dominate only one type of landscape element. Our results show that fallows are most susceptible to invasion and Panicum maximum Jacq. and Chromolaena odorata (L.) R.M.King & H.Rob are the most invasive species in our site. This is fundamental for predicting the future and for the restoration of these very useful ecosystems for biodiversity as well as for the population of the area

Assessment of forest degradation in the Amazon using multi-sensors techniques: the case of Paragominas (Brazil). O-2215-01

The Amazonian pioneer front region is a mosaic of different forests types and agricultural landscapes resulting from the colonization of the region through forest conversion into pasture and agricultural lands. Fearnside and Guimaraes (1996) showed that 47% of the deforested area is rapidly abandoned. It also appears that logged forests surface is equivalent to deforested areas (Asner et al., 2005). Consequently a degradation gradient exists from low impacted logged forests (depending of the logging intensity) to young secondary (regrowth) forests. To obtain more accurate estimation of carbon stocks, it is important today to take into account the degraded forest gradient including all degraded forest stages between mature intact forests and non-forest areas. The first main challenge is to identify and to characterize the various stages. The identification of forest degradation is still a complex and expansive problem even if it has been focused until now only on logged tropical rainforest (Asner, 2009; Gond and Guitet, 2009; Desclées et al., 2006; Asner et al., 2005; Souza et al., 2003). In parallel estimation of biomass loss in the degraded forest is little-studied. Within temperate and boreal forests some estimation are made by Solberg et al., (2013). The combination of optical remotely sensed data (Landsat-8), radar (Terra-Sar-X) and Lidar (IceSat) have to be studied to analyze the potential of the multisensors techniques to characterize the tropical rainforest degradation (Betbeder et al., 2014). The study presents the first results obtained during the field work at Paragominas (Pará, Brazil) on different forest degradation intensities (Bérenguer et al., 2014). This field database is then compared with multi-sensors remote sensing to better understand multiple interactions and to establish a forest degradation typology. (Texte intégral

Occupation du territoire et gestion des ressources naturelles en contexte amérindien : le cas des Wayampi et Teko de Camopi en Guyane française

Les populations amérindiennes expérimentent depuis plusieurs décennies des changements socio-économiques et territoriaux importants, dans un contexte d'augmentation démographique forte. Nous nous intéressons à l'adaptation des systèmes d'occupation du territoire et d'exploitation des ressources naturelles des Amérindiens de Guyane face aux contraintes exercées sur leur territoire et leur mode de vie. Quelle est la résilience des systèmes amérindiens d'utilisation du territoire et de ses ressources naturelles? La concentration de l'habitat amérindien autour du bourg de Camopi, liée à l'implantation des infrastructures de type centre de santé et école, et à la promotion de l'habitat sédentaire, contribue à générer une pénurie des ressources naturelles et un mal-être social. Le système s'adapte par un éclatement de l'habitat en villages périphériques et par une extension des terroirs agricoles le long des cours d'eau, afin de retrouver de l'espace. Ces villages reproduisent un modèle d'organisation spatiale semblable à l'organisation traditionnelle des villages wayampi et teko. L'habitat rest

Occupation du territoire et gestion des ressources naturelles en contexte amérindien : le cas des Wayapi et Teko de Camopi en Guyane française

Les populations amérindiennes expérimentent depuis plusieurs décennies des changements sociaux-économiques et territoriaux importants, dans un contexte d'augmentation démographique forte. Nous nous intéressons à l'adaptation des systèmes d'occupation du territoire et d'exploitation des ressources naturelles des amérindiens de Guyane face aux contraintes exercées sur leur territoire et leur mode de vie. Quelle résilience des systèmes amérindiens d'utilisation du territoire et de ses ressources naturelles ? La concentration de l'habitat amérindien autour du bourg de Camopi, liée à l'implantation des infrastructures de type dispensaire et école, et à la promotion de l'habitat sédentaire, génère une pénurie des ressources naturelles et un mal-être social. Le système s'adapte par un éclatement de l'habitat en villages périphériques et par une extension des terroirs agricoles le long des fleuves, afin de retrouver de l'espace. Ces villages reproduisent un modèle d'organisation spatiale semblable à l'organisation traditionnelle des villages Wayãpi et Teko. L'habitat reste cependant sédentaire, les familles souhaitant voir leur village se faire équiper des services minimum : eau potable et électrification. La limite spatiale à l'éclatement de l'habitat demeure les déplacements journaliers vers l'école, et par conséquent la desserte par le transport scolaire. Ainsi, les services et infrastructures conditionnent l'occupation du territoire. Des abattis complémentaires sont maintenus à plus grande distance du bourg et l'habitat devient bilocal : un habitat principal desservi par les services et infrastructures, et un habitat secondaire, éloigné et itinérant, conditionné par la qualité des terres agricoles, les rendements de chasse, l'histoire du lieu et les réseaux familiaux. Le maintien de ces habitations éloignées est possible grâce à l'investissement des revenus issus des aides sociales dans le transport. Nous montrons ainsi que les systèmes amérindiens d'occupation du territoire et d'exploitation des ressources naturelles ont un potentiel adaptatif fort : ils s'appuient sur la recomposition de mobilités circulaires, organisées selon un gradient d'intensité d'utilisation des ressources, qui garantit la durabilité de leur système. (Texte intégral

Dynamiques territoriales des Amérindiens wayãpi et teko du moyen Oyapock, Camopi, Guyane française

Les populations amérindiennes expérimentent depuis plusieurs décennies des changements socio-économiques et territoriaux importants, dans un contexte d'augmentation démographique forte. L'article aborde l'adaptation des systèmes d'occupation du territoire et d'exploitation des ressources naturelles des Amérindiens de Guyane française face aux contraintes exercées sur leur territoire et leur mode de vie. Quelle est la résilience des systèmes amérindiens d'utilisation du territoire et de ses ressources naturelles ? La concentration de l'habitat amérindien autour du bourg de Camopi, liée à l'implantation des infrastructures de type centre de santé et école, et à la promotion de l'habitat sédentaire, contribue à générer une pénurie des ressources naturelles et un mal-être social. Le système s'adapte par un éclatement de l'habitat en villages périphériques et par une extension des terroirs agricoles le long des cours d'eau, afin de retrouver de l'espace. Ces villages reproduisent un modèle d'organisation spatiale semblable à l'organisation traditionnelle des villages wayãpi et teko. L'habitat reste cependant sédentaire, les familles souhaitant voir leur village se faire équiper des services minimaux : eau potable et électrification. La limite spatiale à l'éclatement de l'habitat demeure les déplacements journaliers vers l'école, et par conséquent la desserte par le transport scolaire (pirogue). Ainsi, les services et infrastructures conditionnent l'occupation du territoire. Des abattis complémentaires sont maintenus à plus grande distance du bourg et l'habitat devient bilocal : un habitat principal desservi par les services et infrastructures et un habitat secondaire, éloigné et itinérant, conditionné par la qualité des terres agricoles, les ressources cynégétiques, l'histoire du lieu et les réseaux familiaux. Le maintien de ces habitations éloignées est possible grâce à l'investissement des revenus issus des aides sociales dans le transport. Il est ainsi montré que les systèmes amérindiens d'occupation du territoire et d'exploitation des ressources naturelles ont un potentiel adaptatif fort : ils s'appuient sur la recomposition de mobilités circulaires, organisées selon un gradient d'intensité d'utilisation des ressources, qui garantit la durabilité du système. (Résumé d'auteur

Uncovering the drivers of landscape change, using ComMod to elicit shifting cultivation livelihood strategies

To foster the resilience of tropical landscapes, we need to understand the agents of change, the stakeholders potentially tipping the system from one state into the next. This forces us to confront the basic question 'Why do people take the decisions they take?' However, finding the answers is nearly as hard as creating the conditions for the question to be properly posed, as complacency bias and the gap between narrative and behaviour could easily lead to skewed results. To work around this issue we used a trans-disciplinary approach called Companion Modelling. This method facilitates the construction of an interactive model, a game, together with the stakeholders. We then used this model to uncover the drivers of change in Karbi Anglong, in North-East India The Karbi tribe have traditionally been practicing Jhum, or shifting cultivation, to meet subsistence needs, and their rights to use the communal forests are protected by the constitution of India. However, the forested hills also provide a refuge for the wildlife of the adjacent Kaziranga National Park, a UNESCO world heritage site. This wetland system floods every monsoon, forcing the animals out of the park and into the Karbi hills. Changes in landscape management by the farmers can have serious implications for conservation. The Jhum farmers have become more aware of alternative development strategies, and might be approaching a tipping point, moving away from traditional subsistence farming and forest dependency, and towards permanent plantations of tea, rubber and bamboo. To set the scene for asking the key question we build a model of the Jhum system, and the resource allocation decisions farmers face when setting out their livelihood strategies. The game puts the farmers in a position that elicits decision making, while it also creates a platform for discussing their strategies, motivations, results and wider implications. (Texte intégral

Mapping ecosystem services at the regional scale: the contribution of an up-scaling approach. The case of the Amazon pioneer front

Background: Large-scale ecosystem services (ES) mapping is a challenge for environmental management. A possible and low-cost method is the up-scaling approach, which we tested on Pará State, Brazil. Method: We mapped four ES indicators (vegetation carbon stocks, rates of water infiltration into soil and a biodiversity and a chemical quality index) at the regional scale, from field and remote sensing data. To do so, we first classified the land cover from MODIS images. Then, we averaged the ES indicators (field data) per MODIS land cover class. Finally, we evaluated regional maps' accuracy through three different procedures: first, we mapped the variability of the ES indicators per land cover type. Secondly, we compared, statistically and visually, the regional ES indicators maps with local scale maps made from statistical models that linked remote sensing (Landsat and DEM Aster) and field (ES indicators) data. Finally, we calculated the correlations between our predicted values and independent datasets. Results: Our results showed the spatial distribution of some ES indicators for Pará Sate. ES indicators providing is the highest in the forest, except the soil chemical quality index. Yet, Pará State, still mainly covered by forests, has known a large movement of deforestation from the east to the west, despite the creation of protected areas. The western part, marginally affected by deforestation, is thus characterized by high ES providing. On the contrary, the eastern part, severely damaged by deforestation, is associated with poor ES providing. Our results also showed the unequal capacity to get reliable ES maps at the regional scale. In other words, our results show the additional complexity of modeling ES whose variations are very partially based on land cover changes, such as the biodiversity index. Discussion: Up-scaling approaches should bridge the gap between the spatial scales. These approaches complete large-scale maps by local knowledge and enable the estimation of the uncertainty of the maps and ES spatial representation at different spatial scales. They then may help to justify conservation actions by targeting the areas greatly damaged. Regional maps for other indicators of ES at the regional scale should be investigated. From this study, one could also decide to implement the proposed methodology to map ES indicators at a larger scale, even up to the global scale, if one possesses sampling data all over the world. (Texte intégral

Understanding the past for the future management: Effects of current and historic land Use on invasive plant diversity in Southeastern Togo, West Africa

Biological invasions and changes in land use are two components of global change affecting biodiversity worldwide. Both contemporary and historic land use may influence the spread of invasive plants by altering landscape patterns, soils, and biotic communities. Indeed, invasion within land uses is often associated with the historical legacy of changes in land use. Like in most West African regions, Togodo Protected Area (TPA) and its peripheries experienced notable land use change over the past few decades. These changes led to the spread of many invasive plants that threaten the biodiversity of the TPA and are chores for local farmers. How- ever, despite the legacy of current and past land uses on plant invasion success, few studies have investigated the mechanisms triggering invasion credit and, in Togo, plant invasion ecology has not yet gained enough attention. In this study, we investigated the influence of the current and historic land uses on the diversity of invasive plants in and around TPA. Firstly, we defined land use change trajectories using land use maps performed from Landsat images acquired in 1974, 1986, and 2003 and from Sentinel 2 image acquired in 2016. Secondly, we conducted botanic surveys in the different land use types and, 198 quadrats of 50 x 50 m were laid to make an inventory of all plant species