2This study compiled recent inventory data from 929,823 street trees in 50 cities to determine 3 trends in tree number and density, identify priority investments and create baseline data against 4 which the efficacy of future practices can be evaluated. The number of street trees increased 5 from 5.9 million in 1988 to 9.1 million in 2014, about one for every four residents. Street tree 6 density declined from 65.6 to 46.6 trees per km, nearly a 30% drop. City streets are at 36.3% of 7 full stocking. State-wide, only London planetree (Platanus x hispanica) comprises over 10% of 8 the total, suggesting good state-wide species diversity. However, at the city scale, 39 9 communities were overly reliant on a single species. The state's street trees remove 567,748 t 10
There has been an increasing interest in urban forests and the levels of biodiversity they contain. Currently there are no spatially explicit maps of tree species richness in urban areas. This research tests and identifies GIS and remote sensing metrics (climate, area, productivity, three-dimensional structure) hypothesized to be associated with species richness in native forests and identifies methods that can be applied to predict and map tree species richness in cities. We quantified tree species richness, floristic composition, and structure in 28 1-ha plots in the city of Los Angeles. Climate and remote sensing metrics from highresolution aerial imagery (10 cm), QuickBird (60 cm), Landsat (30 m), MODIS (250 m), and airborne lidar (2 m) were collected for each plot. There were 1208 individual stems and 108 trees identified to species. Species richness ranged from 2 to 31 species per ha and averaged 17 species per ha. Tree canopy cover from QuickBird explained the highest portion of variance (54%) in tree species richness followed by NDVI from Landsat (42%). Tree species richness can be higher in residential urban forests than native forests in the United States. Spatially explicit species richness maps at 1 ha can be created and tested for cities in order to identify both hotspots and coldspots of tree species richness and changes in species richness over time.
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