Forest Diversity of the Cumaribo Region (Vichada Department) in the Transition Zone between the Amazonia and the Orinoquia of Colombia

Forest vegetation (flooded, semi-flooded, and non-flooded or “terra firme”) of the Cumaribo region was characterized using data from 29 plots. This sector is located in municipality at the Vichada department, and in adjacent areas of the Guainía and Guaviare departments, Colombia. In 1000 m² plots, all individuals with a diameter (DAP) > 10 cm were measured, the basal area (m²⁾, relative abundance (%), and relative dominance (%) were calculated. The latter values helped to estimate the “reduced” importance value index (IVI).The Sigmatist school guidelines were used to classify the forests. According to floristic composition, patterns of structure, and spatial distribution of the species, forests were grouped in class Brosimo lactescentis-Eschweileretea subglandulosae with an estimated basal area of 165.7 m² in 10,579 individuals belonging to 685 species. In Mabeo nitidae-Mespilodaphnetalia cymbari forests (14 plots, 14000 m² of sampled area), the basal area value of 101.9 m² was estimated at 4770 individuals in 348 species, and the Duguetio quitarensis-Amphirrhocion longifoliae alliance covered 55.94 m² at 1901 individuals of 192 species. The association Vitici compressae-Attaleetum butyraceae presented the highest value of dominance index (basal area/sampling area) with 1.2%. In the alliance Virolo surinamensis-Mespilodaphnion cymbari, the basal area was 21.9 m² with 1461 individuals in 138 species. The association Aspidospermo desmanthi-Mespilodaphnetum cymbari presented a basal area of 24.4 m² with 1408 individuals and 211 species. In Phenakospermo guyannenses-Minquartietalia guianensis forests (13 plots, 13000 m²⁾ basal area was 63.8 m² in 5809 individuals and 486 species. These values were provided by the alliance Attaleo maripoae-Iryantherion laevis with its five associations, where the palm association Attaleo maripae-Euterpetum precatoriae showed the highest richness value index with 6.3%. The Micropholio venulosae-Eschweileretum bracteosae forests presented the highest density index with a 0.6 number of individuals/ sampling area. The present study grouped forest vegetation into one class, two orders, 2 alliances, and 10 associations. These results represent the first proposal of a phytosociological classification of the forests located in the transition region of the Orinoquia and the Colombian Amazon.