Using phylogenetic diversity to explore the socioeconomic and ecological drivers of a tropical, coastal urban forest

Relatively little is known about the dynamics of tropical urban forests, their phylogenetic diversity, as well as the socioeconomic and ecological factors that influence overall diversity across the urban landscape. However, permanent forest inventory and monitoring plot networks are increasingly being established across forests and cities of the world to monitor structural and functional attributes of urban forests, as well as ecosystem services. We analyzed a tropical, coastal urban forest in San Juan, Puerto Rico using metrics of phylogenetic diversity (PD), plant diversity, and available permanent plot data from an urban forest inventory and monitoring system. In total, we found 152 species belonging to 119 genera and 44 families in San Juan. PD tended to be highest in forest remnant areas. We also explored correlations between socioeconomic factors and taxonomic diversity and found that plant species richness was correlated with population density and housing price. We found marginally significant relationships between housing price, population density, and several PD metrics. Our results further suggest mixed evidence of luxury and legacy effects, two factors that have been linked to the plant diversity of anthropogenic ecosystems in other research. Overall, despite centuries of human influence, the existing urban forest diversity in San Juan - although perhaps not the particular species composition - is likely to be primarily the result of climate, biome, and multi-scale socioeconomic contexts and not legacy effects. The approach used and findings from this study could be used to better understand the application of PD metrics for assessing urban biodiversity and other beneficial attributes and traits of urban forests.