Abstract

Jebel Marra, a volcanic complex in western Sudan, is an important site of early settled agriculture, with high plant diversity, supported by orographic rainfall. Vegetation types were examined in relation to habitat, altitude, soils, and land management. In 52 sites, 274 species, predominantly Fabaceae and Poaceae, were recorded (with 17 new records). Sites were clustered using TWINSPAN, and Detrended Correspondence Analysis (DCA), generating eight vegetation types, six new since the 1970s. Changes in the dominant species show that the savanna has become sparser, with annuals displacing perennials. Soils were mostly “sandy clay loams,” so vegetation types did not directly correspond to soil types, although Type VIII vegetation grew in soils with a higher clay content. The sand fraction that predominated in soils of all other vegetation types was, mainly (87%) “soft” or aeolian sand. Canonical Correspondence Analysis (CCA) separated communities and species along a first axis, associated with finer soil textures, higher Fe, and lower elevations. The second axis was positively associated with elevated phosphorus, and negatively with sandy loams. CCA showed that rainfall alone was less pertinent than soil texture, which determines plant-available water capacity. The region’s vegetation was not uniformly diverse; instead, a mosaic of patches of diverse terrain, associated with different vegetation “types,” collectively generates a diverse flora. Besides climate change, overgrazing and increasing human pressures due to conflict, local population growth and an influx of refugees place these (already stressed) plant resources at risk. Our survey provides a baseline to track changes and develop adaptive management strategies.

摘要

苏丹西部的火山群杰贝勒·马拉（Jebel Marra）是早期定居农业的重要地点，其高植物多样性受到地形降雨的支持。检查了与栖息地，海拔，土壤和土地管理有关的植被类型。在52个地点中，记录了274种，主要是豆科和禾本科（新增了17条记录）。利用TWINSPAN和去趋势对应分析（DCA）对站点进行聚类，生成了八种植被类型，自1970年代以来新增了六种。优势物种的变化表明，稀树草原变得稀疏，一年生植物取代多年生植物。土壤大多是“沙质壤土”，因此植被类型并不直接对应于土壤类型，尽管VIII型植被生长在粘土含量较高的土壤中。在所有其他植被类型的土壤中占主导地位的沙粒是 主要（87％）是“软”或风沙。典范对应分析（CCA）沿第一轴分离了群落和物种，与更细的土壤质地，更高的铁含量和更低的海拔高度相关。第二轴与磷含量升高呈正相关，与沙壤土呈负相关。CCA显示，仅降雨比土壤质地更不相关，这决定了植物的可用水容量。该地区的植被并不均匀。取而代之的是，与不同植被“类型”相关联的，由不同地形组成的小块马赛克共同生成了多种植物。除了气候变化之外，由于冲突，当地人口增长和难民涌入造成的过度放牧和不断增加的人类压力使这些（已经有压力的）植物资源处于危险之中。