Urban populations are exposed to a variety of environmental health challenges, such as increased exposure to air pollutants, decreased water quality, degraded natural environments, increased psychological stress, increased heat risk, intensified stormwater runoff, and noise and light pollution. One of the most common measures proposed to address these issues is the establishment of urban tree cover and green spaces. Studies have shown that tree canopy cover plays a significant role in urban cooling, and increased access to urban green spaces has been associated with better health outcomes, both in terms of physical and mental health. However, human exposure to these stressors varies across urban areas, and it has been suggested that spatial variations in the amount of natural vegetation cover contribute to environmental and health disparities.
To help address these issues, a pilot study to develop an interactive method for determining where to establish urban trees, as well as to examine the relationships between sociodemographic factors and tree canopy cover, was funded by the Taylor Geospatial Institute. This work used a multidisciplinary approach, combining remote sensing, sociology, and GIS to analyze these factors at a finer resolution than seen in past studies. Statistically downscaled US Census data (1-ha spatial resolution) was used along with high-resolution canopy cover mapped for the St. Louis region to examine social and physical cover dynamics. Sociodemographic, canopy cover, land-cover, and urban trail data were then used to generate suitability overlays for a tree establishment Opportunity Index (OI) under multiple scenarios (see table below). OI values range from 0 to 1, where higher values indicate greater suitability for tree cover establishment.
| Scenarios (Opportunity Index) | Herbaceous cover | Population density | Poverty rate | Trail network | Tree cover | Urban cover density | Wooded cover density | Sum |
|---|---|---|---|---|---|---|---|---|
| Favors populated areas | 0.1 | 0.3 | 0.1 | 0.1 | 0.1 | 0.1 | 0.2 | 1 |
| Favors populated areas & socio-demographics | 0.1 | 0.25 | 0.25 | 0 | 0.1 | 0.2 | 0.1 | 1 |
| Favors highly developed areas | 0.15 | 0.15 | 0.1 | 0.1 | 0.1 | 0.3 | 0.1 | 1 |
| Favors trails | 0.1 | 0.1 | 0.1 | 0.3 | 0.1 | 0.2 | 0.1 | 1 |
| Favors trails & socio-demographics | 0.1 | 0.15 | 0.2 | 0.25 | 0.1 | 0.1 | 0.1 | 1 |
Variable Descriptions:
| Variable | Description |
|---|---|
| Herbaceous cover | Derived from MoRAP 10m land cover for EWG. Ecological types that were classified as herbaceous, barren, or sparsely vegetated types were given preference. Highest preference given to such types in urban areas. Individual suitability as follows: Barren or Sparsely: 0.5, Bottomland Herbaceous: 0.5, Bottomland Successional: 0.5, Cultural Disturbance x3: 0.5, Developed herbaceous: 1, Disturbance Successional Upland grassland: 0.5 (excludes wetlands and glades). |
| Population density | Rasterized from US Census population density downscaled to 1 ha hexagons. |
| Poverty rate | Rasterized from US Census poverty rate downscaled to 1 ha hexagons. |
| Trail network | Distance to Great River Greenway trail system in meters. |
| Tree cover | 10 m to percentage tree coverage for entire area. Represents within pixel tree density (10 m assumed to be 100%). Values calculated inversely – lower pixel tree density (or no tree present) = higher preference for new tree establishment. |
| Urban cover density | Derived from MoRAP 10m land cover for EWG. Urban types polygonised, centroids attributed by polygon area, and kernel density calculated using centroid points with area weighting. |
| Wooded cover density | Based on kernel density using area weighted points from polygonised cover rasters. Areas further from densely wooded areas favored. As opposed to trees layer, global rather than local density |
(Downscaled US Census data were produced and provided by Ness Sandoval of Saint Louis University, and mapped cover products were produced by the University of Missouri – Missouri Resource Assessment Partnership (MoRAP) as part of a recent project with East-West Gateway Council of Governments.)