Biogeographic Disconnect and Biotic Homogenization in the Heart of the Amazon: Dominance of Exotic Species in Urban Trees

Abstract

Urban flora is essential for maintaining biodiversity in urban areas, but there is still a knowledge gap, especially in tropical metropolises. Our hypothesis is that there is a dominance of exotic species used in the landscaping of squares, which promotes biotic homogenization, driven by cultural and aesthetic preferences. We believe that larger and older squares have less dominance and greater species diversity. This study investigated the composition, diversity, and representativeness of Amazonian flora across 35 public squares in Manaus, Central Amazonia. We recorded all specimens with a diameter at breast height (DBH) ≥ 5 cm. We recorded 1218 individuals from 88 species and 31 families. Species origin was classified by biogeographic region, with only Amazonian taxa considered native. Exotic species predominated (61.4%). Notably, 15 exotic species with invasive potential were identified, posing significant risks to local biodiversity. We tested the influence of square area and age on community structure. Area was the sole significant predictor of richness, whereas larger and older squares exhibited higher dominance by a few species, such as Mangifera indica (mango) and Moquilea tomentosa (oitizeiro). Age was the only significant negative predictor of alpha diversity. Beta diversity was not influenced by any predictor, indicating a highly homogenized species pool. Urgent management actions are needed that consider both individual squares and the broader landscape to gradually replace exotic and invasive species with native Amazonian species while aligning with the preferences of local residents, thereby restoring ecological functions and enhancing the conservation of urban forests.