The woodland vegetation of the Katavi-Rukwa ecosystem in western Tanzania

We describe tree diversity, forest community composition and vegetation structure in dry forest miombo woodland in the Katavi-Rukwa ecosystem of western Tanzania. Tree diversity was high (45 families, 117 genera, 229 species) and concentrated in the Fabaceae (30 genera, 73 species). A strong majority (75%) of 19,481 sampled trees were aggregated in just 12 genera spread among 11 families, with individuals in the genera Grewia (17.42%), Markhamia (13.20%) and Combretum (13.13%) dominating abundance. Assessing dominance in terms of a combined importance value (IV300, summed relative abundance, basal area and frequency), showed Terminalia sericea, Combretum adenogonium, and C. colinum as the dominant tree species. Thus, woodlands in this region are atypical of the miombo biome in which it is embedded with only six of fifty 0.1 ha quantitative plots dominated by species in one of the classic miombo genera (Brachystegia, Julbernardia, or Isoberlinia). Ordination of data from these 50 plots revealed a diffuse structure of communities. Moreover, trees were found to be spatially clumped within, as well as among, plots. By documenting how the Katavi-Rukwa ecosystem is comprised of a patchwork of locally dominant common trees intermixed with a diverse assemblage of less common species, which have few specific associations with particular dominants, our study begins to fill an important gap in understanding composition and structure of dry forests that still occupy so much of southern-central Africa.