In a changing world where urbanization is the dominant trend in land-transformation, novel ecosystems emerge as natural response to the new environmental conditions promoted by human activity. Forests in Puerto Rico have a long history of disturbance and the exotic species are a common component. It is estimated that 75% of forests on the island are novel forests and the introduced and naturalized species represent among 20% to 23% of the flora. These novel forests provide multiple ecological services. In this study, I examine: 1) What is the habitat structure in green areas from different land-uses distributed in an urbanized landscape? 2) What is the human influence and the legacy of human use in the habitat structure patterns? To address these questions, I selected 30 sites to represent green areas from five (5) land covers (mature forest, young forest, shrubland, pasture, and yard), distributed in an urban and suburban landscape in the northeast of Puerto Rico, and I compared habitat structure in those sites.
I identified a total of 104 woody plant species from 41 families. Total richness was relatively similar between suburban (76 sp) and urban area (65 sp). Mature and young forests were the covers with higher richness and shared a high proportion of species. Native species represented 47.12% of all species identified. Suburban area had a higher number of native species (57.9%) compared with urban area, where exotics tend to be more common (58.5%). Ground in mature and young forests was mainly cover by litter, while bare soil dominated in shrublands and pastures, and herbaceous vegetation and artificial elements were the dominant elements on the yards. Habitat structure differed between green areas and it tended to increase in complexity from more open areas (pasture) to zones with more woody vegetation (mature forest), and from more disturbed to less modified area through the urban gradient. Main differences were recorded in the understory layer between urban and suburban young forests. Changes in the heterogeneity and complexity of habitats between site reflected a high and diverse mix of characteristics associated with native and introduced species that characterize novel and evolving floral assemblages in Puerto Rico, and which provide multiple ecological services.