Spatial Heterogeneity in Tree Diversity, Floristic Differentiation, and Forest Structure Across Four Andean–Amazonian Foothill Stands in Southwestern Peru

Tropical foothill forests are heterogeneous transition zones, yet field inventories remain sparse in the Andean–Amazonian region. We compared four forest stands to establish a local biodiversity baseline and determine whether tree diversity, floristic differentiation, and stand structure showed similar descriptive patterns. Four 0.25-ha plots located between 239 and 487 m a.s.l. in Madre de Dios, Peru, were inventoried for trees with diameter at breast height ≥ 10 cm. Diversity was characterized using Hill numbers, floristic differentiation using coverage-standardized beta diversity, and forest structure and soil properties descriptively. We recorded 532 trees representing 163 species, 97 genera, and 34 families. Observed richness ranged from 56 to 68 species, whereas abundance-weighted diversity varied more markedly. At 84% sample coverage, richness-based Sørensen-type and Jaccard-type dissimilarities ranged from 0.251 to 0.602 and from 0.401 to 0.752, respectively. Structural attributes varied among plots but did not follow the same ordering as diversity or floristic differentiation. Soil properties were treated solely as environmental context because each plot had one composite sample. The findings document heterogeneity among the four sampled stands and provide a sampling-standardized baseline for this poorly documented foothill sector, without establishing regional patterns or environmental causes.