The variation of vegetation structure and greenness in Central Africa: Combining MODIS multi-temporal data with six million hectares of forest inventory (original) (raw)
Related papers
Vegetation structure and greenness in Central Africa from Modis multi-temporal data
Philosophical Transactions of the Royal Society B: Biological Sciences, 2013
African forests within the Congo Basin are generally mapped at a regional scale as broad-leaved evergreen forests, with the main distinction being between terra-firme and swamp forest types. At the same time, commercial forest inventories, as well as national maps, have highlighted a strong spatial heterogeneity of forest types. A detailed vegetation map generated using consistent methods is needed to inform decision makers about spatial forest organization and their relationships with environmental drivers in the context of global change. We propose a multi-temporal remotely sensed data approach to characterize vegetation types using vegetation index annual profiles. The classifications identified 22 vegetation types (six savannas, two swamp forests, 14 forest types) improving existing vegetation maps. Among forest types, we showed strong variations in stand structure and deciduousness, identifying (i) two blocks of dense evergreen forests located in the western part of the study a...
Vegetation Dynamics in the Upper Guinean Forest Region of West Africa from 2001 to 2015
Remote Sensing, 2016
The Upper Guinea Forest (UGF) region of West Africa is one of the most climatically marginal and human-impacted tropical forest regions in the world. Research on the patterns and drivers of vegetation change is critical for developing strategies to sustain ecosystem services in the region and to understand how climate and land use change will affect other tropical forests around the globe. We compared six spectral indices calculated from the 2001-2015 MODIS optical-infrared reflectance data with manually-interpreted measurements of woody vegetation cover from high resolution imagery. The tasseled cap wetness (TCW) index was found to have the strongest association with woody vegetation cover, whereas greenness indices, such as the enhanced vegetation index (EVI), had relatively weak associations with woody cover. Trends in woody vegetation cover measured with the TCW index were analyzed using Mann-Kendall statistics and were contrasted with trends in vegetation greenness measured with EVI. In the drier West Sudanian Savanna and Guinean Forest-Savanna Mosaic ecoregions, EVI trends were primarily positive, and TCW trends were primarily negative, suggesting that woody vegetation cover was decreasing, while herbaceous vegetation cover is increasing. In the wettest tropical forests in the Western Guinean Lowland Forest ecoregion, declining trends in both TCW and EVI were indicative of widespread forest degradation resulting from human activities. Across all ecoregions, declines in woody cover were less prevalent in protected areas where human activities were restricted. Multiple lines of evidence suggested that human land use and resource extraction, rather than climate trends or short-term climatic anomalies, were the predominant drivers of recent vegetation change in the UGF region of West Africa.
The past protecting the future : Locating climatically stable forests in West and Central Africa
International Journal of Climate Change Strategies and Management, 2009
Purpose -In answer to the urgent need to adapt conservation strategies and approaches to climate change, the purpose of this paper is to locate the climatically stable forests in West and Central Africa and to assess whether they overlap with the existing network of protected areas and if not, to prioritize them for protection. Design/methodology/approach -With ongoing global warming, rain forest will survive where locally soil moisture content remains high compensating for the regional drought stress. As a proxy for a soil moisture-driven model, rainfall . 2,000 mm, altitude .500 m and strong relief (standard deviation in elevation data pixels) were overlapped in a GIS analysis to locate the climatically stable forest within the present continuous forest of Central Africa and within the degraded forest of West Africa. As a means of verification, the biodiversity was measured in and outside the identified areas in Gabon and Equatorial Guinea as high levels of biodiversity are related to the survival and stability of the forest in the past. Biodiversity was calculated (measured as Fisher-a diversity) for all trees (dbh .5 cm) on 66 transects (200 £ 5 m). Findings -The forest areas identified as climatically stable in the GIS analysis showed a higher biodiversity than the forest outside these areas (student T-test: P , 0.000035, stable ¼ 54.7 and unstable ¼ 33.7), supporting the validity of the model. Mapping the results of the GIS query showed that most of the climatically stable forests in West and Central Africa are located outside the park systems, and that it is already too late to protect the climatically stable forest in West Africa as almost nothing is left of it. Originality/value -Wedged in between large-scale drought tolerant ecosystems the African rain forest is most vulnerable to global climate change. Knowing which parts are climatically stable and resilient helps to set and focus conservation priorities and efforts. This approach is a powerful tool which has helped to identify areas with a high-conservation priority in Africa.
Journal of Tropical …, 2008
Understanding how species assemblages are structured in relation to environmental variation is a central issue in community ecology. However, factors that create regional variation in relative species abundances have been little studied due to the rarity of large-scale datasets. Here, we investigated a large dataset (30 180 0.5-ha plots spread over 1 600 000 ha) gathered from forest planning inventories in the semi-deciduous forest of the south western Central African Republic. We used Correspondence Analysis and Non-Symmetric Correspondence Analysis on Instrumental Variables to analyse variation in the abundance of 73 common tree species in relation to soil type, rainfall and proximity to villages. Together, environmental variables explained 10.3% of multi-species floristic variation among plots, and the regional spatial structure almost disappeared when the effects of these variables were removed. A Trend Surface Analysis using a third order polynomial function of the geographical coordinates of the plots explained 14.5% of the floristic variation and more than 75% of this variation was explained by environmental variables. Sandy soil was the most influential factor affecting floristic composition. Residual spatial variation not explained by the environmental variables probably reflects the natural and anthropogenic history of the vegetation.
Forest Ecosystems, 2016
Background: Tropical dry forests cover less than 13 % of the world's tropical forests and their area and biodiversity are declining. In southern Africa, the major threat is increasing population pressure, while drought caused by climate change is a potential threat in the drier transition zones to shrub land. Monitoring climate change impacts in these transition zones is difficult as there is inadequate information on forest composition to allow disentanglement from other environmental drivers. Methods: This study combined historical and modern forest inventories covering an area of 21,000 km 2 in a transition zone in Namibia and Angola to distinguish late succession tree communities, to understand their dependence on site factors, and to detect trends in the forest composition over the last 40 years. Results: The woodlands were dominated by six tree species that represented 84 % of the total basal area and can be referred to as Baikiaea-Pterocarpus woodlands. A boosted regression tree analysis revealed that late succession tree communities are primarily determined by climate and topography. The Schinziophyton rautanenii and Baikiaea plurijuga communities are common on slightly inclined dune or valley slopes and had the highest basal area (5.5-6.2 m 2 ha −1). The Burkea africana-Guibourtia coleosperma and Pterocarpus angolensis-Dialium englerianum communities are typical for the sandy plateaux and have a higher proportion of smaller stems caused by a higher fire frequency. A decrease in overall basal area or a trend of increasing domination by the more drought and cold resilient B. africana community was not confirmed by the historical data, but there were significant decreases in basal area for Ochna pulchra and the valuable fruit tree D. englerianum. Conclusions: The slope communities are more sheltered from fire, frost and drought but are more susceptible to human expansion. The community with the important timber tree P. angolensis can best withstand high fire frequency but shows signs of a higher vulnerability to climate change. Conservation and climate adaptation strategies should include protection of the slope communities through refuges. Follow-up studies are needed on short term dynamics, especially near the edges of the transition zone towards shrub land.