Understanding drivers of urban tree biodiversity in Los Angeles

Background/Question/Methods

Urban tree diversity is strongly affected by decisions to plant specific species, particularly in afforested regions where urban trees are virtually all planted. The various factors that affect attitudes and preferences about species are not well understood. In addition, the linkages between the preferences of urban residents and actual tree species composition in neighborhoods have not been investigated. Here we address two questions: 1) do socioeconomic and/or local environmental factors affect attitudes towards tree attributes, and 2) to what extent are these attitudes reflected in actual tree biodiversity. To address these questions, we surveyed residents of 5 counties in southern California about tree attributes. We used structural equation modeling to determine the relative effects of socio-demographic variables (age, income, education and gender) and local environmental data (temperature, rainfall, elevation, and distance from coast) on participant’s attitudes towards tree attributes. To address our second question, we compared survey responses within the city of Los Angeles with an urban forest inventory. Trees were categorized as evaluated in the survey, such as for the provision of shade or aesthetic qualities such as flowers. We assessed correlations between survey responses and the proportion of trees that possessed those traits in the respondent’s neighborhood.

Results/Conclusions

We found socioeconomic and local environmental factors affected attitudes towards tree attributes. Certain attributes (beauty and provision of fruits) were affected only by socioeconomic variables. All other attributes were affected by environmental factors. Respondent’s attitude towards shading was affected by income (p < 0.01), gender (p < 0.01), and temperature (p = 0.03); participants from warmer climates valued shading more than those from cooler climates. Attitudes toward tree water use were affected by age (p = 0.01), gender (p <0.01), and rainfall (p = 0.05); participants from wetter climates were less concerned with water use compared with those from drier climates. We also found a higher percentage of shade trees in neighborhoods where residents valued shade trees (r = 0.626; p = 0.01), and a greater proportion fruit trees where residents associated trees with providing fruit (r = 0.558; p = 0.03). However, we found no relationship between attitudes toward water use and the proportion of trees that have low water use. Overall, our results demonstrate that local environments affect attitudes about trees, and these values are reflected in neighborhood tree community composition. Our study sheds light on the factors that control biodiversity and biogeography in planted urban forests.