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This study deals with land use and land cover changes for a 33 years period. We assessed these changes for eight land cover classes in the south of Benin by using an integrated multi-temporal analysis using three Landsat images (1972 Landsat MSS, 1986 Landsat TM and 2005 Landsat ETM+). Three scenarios for the future were simulated using a first-order Markovian model based on annual probability matrices. The contribution of tree plantations to compensate forest loss was assessed. The results show a strong loss of forest and savanna, mainly due to increased agricultural land. Natural woody vegetation ("forest", "wooded savanna" and "tree and shrub savanna") will seriously decrease by 2025 due to the expansion of agricultural activities and the increase of settlements. Tree plantations are expected to double by 2025, but they will not compensate for the loss of natural woody vegetation cover. Consequently, we assist to a continuing woody vegetation area decrease. Policies regarding reforestation and forest conservation must be initiated to reverse the currently projected tendencies. ; La présente étude traite des processus de changements d'occupation et d'utilisation du sol sur une durée de 33 années. Ces changements ont été évalués pour huit classes d'occupation du sol au sud de Bénin à partir d'une analyse multitemporelle de trois images satellitaires de type Landsat MSS 1972, Landsat TM 1986 et Landsat ETM+2005. Trois scénarii ont été simulés à partir d'une chaîne de Markov de premier ordre basée sur des matrices de probabilité. La contribution des plantations forestières en vue de compenser les pertes de végétation naturelle a été évaluée. Les résultats indiquent une perte importante des végétations naturelles boisées ("forêt", "savane boisée" et "savanes arborée et arbustive"), principalement due à une augmentation des superficies agricoles. Les végétations naturelles boisées seront drastiquement réduites jusqu'en 2025 au profit des exploitations agricoles et des habitations. Les plantations forestières pourraient doubler leur superficie en 2025, mais elles ne pourront pas compenser les pertes de végétation naturelle boisée. Par conséquent, on assistera à une dégradation constante des végétations naturelles boisées. Des politiques de développement durable basées sur le reboisement et la conservation des forêts doivent être initiées en vue d'inverser les tendances actuelles. ; Peer reviewed

Anthropogenic effects on rodent richness, diversity, abundance, and relative density were studied in 4 habitats of the Masako Reserve, situated in the northeastern part of the Democratic Republic of the Congo. A primary forest dominated by Gilbertiodendron dewevrei as well as 3 anthropogenic habitats (secondary forest, fallow land, and the edge zone situated between the fallow land and the secondary forest) were sampled for rodents between May 2009 and April 2010. 1275 specimens (24 species and 5 families) were captured to quantify the differences in composition and abundance between the non disturbed habitat and the anthropogenic habitats, and between the edge zone and its adjacent habitats. Results indicated a non uniform rodent distribution across the four habitats. Richness and diversity were high in the edge habitat and low in the primary forest. Every habitat was characterized by a different relative density, of which the highest values were observed for the secondary forest and for the fallow habitat; the lowest value was observed for the primary forest. Edge zone characteristics differed from the adjacent habitats which suggested the existence of edge effects. Abundances differed significantly between habitats except between the secondary forest and the fallow land. The low evenness values observed in all habitats reflected the relative instability of the ecosystems at study. A chi-squared test confirmed the existence of seasonal effects on rodent abundance; the impact of anthropogenic activities on rodent presence was shown in the same way for the anthropogenic habitats but not for the primary forest habitat. © Léon Iyongo Waya Mongo, Marjolein Visser, Charles De Cannière, Erik Verheyen, Benjamin Dudu Akaibe, Joseph Ulyel Ali-Patho and Jan Bogaert. ; SCOPUS: ar.j ; info:eu-repo/semantics/published

Context: Wood specific gravity is a key element in tropical forest ecology. It integrates many aspects of tree mechanical properties and functioning and is an important predictor of tree biomass. Wood specific gravity varies widely among and within species and also within individual trees. Notably, contrasted patterns of radial variation of wood specific gravity have been demonstrated and related to regeneration guilds (light demanding vs. shade-bearing). However, although being repeatedly invoked as a potential source of error when estimating the biomass of trees, both intraspecific and radial variations remain little studied. In this study we characterized detailed pith-to-bark wood specific gravity profiles among contrasted species prominently contributing to the biomass of the forest, i.e., the dominant species, and we quantified the consequences of such variations on the biomass. Methods: Radial profiles of wood density at 8% moisture content were compiled for 14 dominant species in the Democratic Republic of Congo, adapting a unique 3D X-ray scanning technique at very high spatial resolution on core samples. Mean wood density estimates were validated by water displacement measurements. Wood density profiles were converted to wood specific gravity and linear mixed models were used to decompose the radial variance. Potential errors in biomass estimation were assessed by comparing the biomass estimated from the wood specific gravity measured from pith-to-bark profiles, from global repositories, and from partial information (outer wood or inner wood). Results: Wood specific gravity profiles from pith-to-bark presented positive, neutral and negative trends. Positive trends mainly characterized light-demanding species, increasing up to 1.8 g.cm-3 per meter for Piptadeniastrum africanum, and negative trends characterized shade-bearing species, decreasing up to 1 g.cm-3 per meter for Strombosia pustulata. The linear mixed model showed the greater part of wood specific gravity variance was explained by species only (45%) followed by a redundant part between species and regeneration guilds (36%). Despite substantial variation in wood specific gravity profiles among species and regeneration guilds, we found that values from the outer wood were strongly correlated to values from the whole profile, without any significant bias. In addition, we found that wood specific gravity from the DRYAD global repository may strongly differ depending on the species (up to 40% for Dialium pachyphyllum). Main conclusion: Therefore, when estimating forest biomass in specific sites, we recommend the systematic collection of outer wood samples on dominant species. This should prevent the main errors in biomass estimations resulting from wood specific gravity and allow for the collection of new information to explore the intraspecific variation of mechanical properties of trees. ; Peer reviewed

Key message: Wood density profiles revealed significant differences in wood formation along a precipitation gradient in the Congo Basin. The response of trees to climate change varies depending on leaf phenology properties. Abstract: Tropical forests face increasing pressures due to climate change and yet, the response of trees to varying climate conditions remains poorly understood. In the present study, we aim to fill some gaps by comparing the leaf phenology and the pith-to-bark wood anatomical variability of 13 common tree species of the Democratic Republic of Congo among three sites presenting contrasted rainfall regimes. We measured pith-to-bark density profiles on which we applied wavelet analyses to extract three descriptors, which we further used as proxies to describe and compare wood anatomical variability. They describe the growth periodicity, regularity and the amplitude of variations of the anatomical patterns. Our results show that evergreen species tend to have significantly higher anatomical variability where rainfall seasonality is more pronounced. Deciduous species, in spite of shedding leaves for longer periods in drier sites, did not show significant differences in their anatomical variability. The analyses of density profiles and phenology records suggest that the seasonality of precipitation influences both leaf phenology and cambial activity. The high intra-site variability in phenology and anatomy suggests that site-related micro-climate conditions also influence cambial activity. ; SCOPUS: ar.j ; info:eu-repo/semantics/published