Urban forest biodiversity and cardiovascular disease: Potential health benefits from California’s street trees

spatial autocorrelation by calculating the Moran statistic and estimate the direct, indirect, and total effect of the Shannon Index on mortality, by year, using the spreg command in Stata 14 as a sensitivity check. The spreg command uses maximum likelihood to estimate a linear model that includes spatial lags of the Shannon Index and error term. We also use the binscatter com- mand in Stata to create binned scatter plots [51] All calculations were done in Stata version 14. To accommodate the possibility of non-linear relationships between biodiversity and mor- tality, we use an alternative specification that includes binary variables for each quantile of the Shannon index. The interpretation of the coefficients for these quantiles would be the differ- ence in mortality when moving from the lowest quantile, Shannon I, omitted, to the quantile associated with the coefficient. yit ¼ a þ g1ShannonIIi þ g2ShannonIIIi þ g3ShannonIVi þ b2Treesi þ �z þ �t þ �it ð3Þ To isolate the effect of biodiversity from that of trees, we also estimate the interaction of bio- diversity quantiles with trees per 100,000 individuals. We carry out a range of sensitivity checks against our parsimonious specification to further address risks from confounders. In addition to the regression with spatially correlated errors, described above, we assess the sensitivity of our estimates to: i) our measure of diversity, by Fig 2. Histograms of Shannon index and trees per hundred thousand individuals. Notes: Data for 857 zip codes in Heart Disease sample California from

consortium of private tree maintenance companies. https://doi.org/10.1371/journal.pone.0254973.g002 PLOS ONE Biodiversity and cardiovascular disease PLOS ONE | https://doi.org/10.1371/journal.pone.0254973 November 3, 2021 8 / 23