Linking Tree Diversity, Stand Structure and Environmental Gradients Across Contrasting Miombo Land‐Cover Types

ABSTRACT Miombo woodlands form a broad African woodland biome that includes substantial internal variation in canopy cover, stand structure and species composition. This study assessed tree diversity, stand structural attributes, DBH size‐class contribution, floristic similarity and environmental drivers across closed woodland, open woodland and wooded grassland within the miombo landscape of Itulu Hill Nature Forest Reserve, Tanzania. A total of 90 plots were surveyed, with 30 plots established in each land‐cover type. Tree species diversity was assessed using species richness, Shannon diversity, Simpson diversity and Pielou evenness. Stand structure was evaluated using stem count, stocking, DBH, basal area, volume, above‐ground biomass and carbon stock. Species accumulation, rarefaction, NMDS, PERMANOVA, Jaccard and Sørensen similarity indices, dominant‐species contribution analysis, and distance‐based redundancy analysis were used to assess sampling completeness, floristic composition, and environmental relationships. A total of 1975 individual trees representing 105 species were recorded. Closed woodland had the highest total number of individuals and species, followed by open woodland, while wooded grassland had the lowest richness. Plot‐level diversity indices did not differ significantly among land‐cover types, although accumulation and rarefaction indicated richer assemblages in closed and open woodland than in wooded grassland. Mean DBH differed significantly among land‐cover types, whereas most other stand‐level attributes did not. Small DBH classes dominated stem count and stocking, while intermediate and larger classes contributed most to basal area, volume, above‐ground biomass and carbon stock. Dominant miombo taxa made large contributions to stand structure and biomass. Tree species composition differed among land‐cover types, although the effect was modest, and the significant dispersion test requires cautious interpretation. Elevation, terrain ruggedness and soil bulk density were significantly associated with species composition. The results indicate that land‐cover types within the same miombo ecosystem can show similar local tree diversity while differing in size structure, floristic composition and environmental relationships.