Plant species richness and abundance in residential yards across a tropical watershed: implications for urban sustainability

Green spaces within residential areas provide important contributions to the sustainability of urban systems. Therefore, studying the characteristics of these areas has become a research priority in cities worldwide. This project evaluated various aspects of the plant biodiversity of residential yards (i.e., front yards and back yards within the Rio Piedras watershed in the San Juan metropolitan area of Puerto Rico). Our work included gathering information on vegetation composition and abundance of woody species (i.e., trees, shrubs, palms, ferns) and large herbs (>2 m height), species origin (native vs. introduced), and species uses (ornamental, food, and medicinal plants). A total of 424 yards were surveyed within an area of 187,191 m(2). We found 383 woody species, with shrubs being the most abundant plant habitat. As expected, residential yards hosted a disproportionate amount of introduced species (69.5%). The most common shrub species were all non-native ornamentals, whereas the most common tree species included food trees as well as ornamental plants and two native species. Front yards hosted more ornamental species per unit area than backyards, while the latter had more food plants. The high amount of introduced species may present a challenge in terms of implementation of plant conservation initiatives if there is no clear definition of urban conservation goals. On the other hand, the high frequency of yards containing food plants may facilitate the development of residential initiatives that could provide future adaptive capacity to food shortages.