Over the last three decades, vegetation surveys in southwest Arabia have documented the existence of a small number of valley forest patches. A well-known area is in Wadi Rijaf, Jabal Bura, a protected area which has recently been surveyed by the current authors. The other valley forest sites in southwest Arabia have not been surveyed for over 15 years. This paper presents a descriptive study of five of these important valley forest localities. To provide an assessment of conservation value, field studies recorded the extent, quality and composition of the vegetation and the presence of regionally rare species. The significance of these remaining patches of Arabian forest, and the immediate threats to their survival, are also discussed.

The isolated massif Jabal Bura (Yemen) is home to the largest area of ‘valley forest’ in southwest Arabia's western escarpment mountains. This study surveys the composition of this very rare forest and records the diversity of vascular plant species. It notes the valley forest as the home of several regionally rare species and records new locations for these taxa. A brief analysis of the canopy layer is provided, enabling comparisons with similar vegetation in northeast Africa. The paper discusses the importance of this regionally rare vegetation as well as threats to its conservation.

The purpose of the present study was to investigate the correlations between environmental variables related to the substrate (soil and topography) and the distribution of tree species in a valley forest in the Chapada dos Guimarães National Park, Mato Grosso State, Brazil. The forest lies in the Cerrado Domain of Central Brazil where the dominant vegetation cover is cerrado (woody savanna). A survey of the tree community registered all live individuals with circumference at breast height (cbh)≥15cm found in eighteen 600m2 plots (total area 1.08ha). The substrate variables used in the gradient analyses were obtained from a topographic survey and from analyses of the chemical and physical properties of soil samples. A principal components analysis of soil and topography variables and a canonical correspondence analysis of the species–environment relationships produced similar results, separating both the substrate variables and the tree species abundances, mainly according to the two types of bedrock, sandstone or slate, underlying their soils, and secondly to the three topographic sectors recognized: Streamside, Mid Slope and Upper Slope. The differences in soil fertility and texture (related to the bedrocks) and the soil water regime (related to both soil texture and topography) were probably the chief factors determining the distribution of tree species in the forest.