Savannization Processes in Tropical Africa (TAGELAQP/SAPITA 91-92)

对1989- 1990年非洲大草原季节研究获得的实地数据进行了分析，并发表在一份出版物中，其中包括以下结果：1)东喀麦隆森林/稀树草原接触：基于半落叶林和廊道林的结构组成与土壤剖面的关系，构建了稀树草原化过程的模型。2)西喀麦隆高地：花粉分析和岩心放射性碳定年表明，森林退化之后的稀树化始于距今3000 - 2500年，自距今2000 - 1500年以来加剧。山地森林元素Podocarpus在LGM期间向低海拔地区扩展。(3)建立了西喀麦隆高原放牧草地退化模式和过程模型。4)苏丹-萨赫勒稀树草原地带：在人类影响增加和持续干旱的情况下，试图制定渐进式土地退化。近年来，由于刀耕火种的休耕期缩短和对保留森林的非法开采，湿润森林的砍伐速度大大加快。南部非洲（赞比亚、津巴布韦和马拉维）6)赞比亚西部：土壤剖面的地质生态学分析和埋藏土壤的放射性碳测年表明，在喀拉哈里沙漠上造成“miombo”林地的人类影响可以追溯到2500年前，从1000年前开始广泛存在，从400年前开始加剧。大约500年前，冶炼铁的人们为了获取薪材而砍伐了常绿的山地森林，导致了广泛的土壤退化，高原上大片的草地由此形成。在整个赤道非洲，迄今可获得的数据表明，自3000 - 2500年前以来，由于人类活动和气候干旱化的耦合影响，森林植被和稀树草原的退化一直在进行。然而，重建更详细的历史需要更准确的年代数据。最近的撒哈拉以南干旱似乎是由对流活动减少引起的，可能与全球尺度的Walker环流异常有关。“沙漠化”和稀树化引起的地表-大气相互作用变化及其气候和生态影响仍然没有答案。少

The field data obtained from the 1989-90 season research in the African savannas were analyzed and were featured into a publication that includes following results :1. Northern Africa (Cameroon)1) East Cameroon forest/savanna contact : A model for explaining savannization processes was constructed on the basis of the relationship between the structure and composition of semideciduous and gallery forests and soil profiles.2) West Cameroon Highlands : Pollen analysis and radiocarbon datings of cores indicate that forest degradation followed by savannization began at 3, 000-2, 500 yr BP and intensified since 2, 000-1, 500 yr BP. Spreading of Podocarpus, a montane forest element, during the LGM to the lower elevations was also confirmed.3) West Cameroon Highlands : A model showing patterns and processes of land and vegetation degradation over cattle-grazed grassy slope was constructed.4) Sudano-Sahelian savanna zone : An attempt was made to formulate progressive land degradation under cond … More itions of increased human impact and persistent drought.5) Recently, deforestation of humid forests has been greatly accelerated due to shortened fallow period of slash-and-burn cultivation and to illegal exploitation of reserved forests.2. Sothern Africa (Zambia, Zimbabwe and Malawi)6) West Zambia : Geoecological analysis of soil profiles and radiocarbon dates of buried soils suggest that human impact creating "miombo" woodland over the Kalahari Sands dates back to to 2, 500 yr BP, widespread from 1, 000 yr BP and intensified from 400 yr BP.7) Nyika Plateau : Widespread grasslands over the plateau have been derived from clearing of evergreen montane forests some 500 years ago for fuelwood by iron-smelting peoples, resulting in widespread soil degradation.3. Throughout equatorial Africa, hitherto available data indicate that the degradation of forest vegetation and savannization have proceeded by the coupled effects of human activities and climatic aridification since 3, 000-2, 500 yr BP. Reconstruction, however, of more detailed history, call for more well-dated data.4. Recent Subsaharan drought seems to be caused by decreased convective activities and may relate with a global-scale anomaly of Walker Circulation.5. Landsurface-atmosphere interaction changes induced by "desertification" and savannization and their climatic and ecological implications remain unanswered. Less