While the factors that determine the distribution of species in natural ecosystems are relatively well understood, we are lacking a strong conceptual framework for the spatial distribution, diversity, and function of urban plants.
Climatic variables likely play a role in the distribution of species and their physiological and ecological function in urban environments; however, factors that affect decision-making, landscape preferences, and institutional rules are also likely to be extremely important. In this project we are mapping the species composition, cover, and leaf area of the urban forest of Los Angeles both with current inventories and with historical analyses of photos, historical records, and satellite images. We are continuing to measure physiological processes of urban trees to develop a functional diversity classification and evaluate species responses to climatic gradients and management intensity. We are also quantifying phenology, greenness, and the Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) with satellite imagery. Finally, we will conduct surveys and focus groups with forest managers, nursery professionals, and urban residents stratified by income and ethnicity in order to evaluate major factors influencing choices and preferences for specific species and functional groups. This coupled with a reconstruction of the tree types planted over time in Los Angeles and the history of the nursery trade, should provide additional dimensions to explaining the trees grown in the region.
Our measurements are designed to test hypotheses about urban forest development, function, and decision-making at several spatial and temporal scales. We will apply our results to developing an agent-based model of decision-making coupled to an ecological model of canopy processes and ecosystem function. Our overall goal is to test a conceptual framework for urban plant biogeography that involves both plant-environment interactions and canopy physiology as well as cultural preferences, institutional rules, and economic factors.