Image credits: Gigi Ling, Unsplash
An urban forest is a collection of trees growing within a city. Urban forests can range from remnant native forest patches to trees planted throughout cities in streets, highways, and backyards.
Trees provide vertical structure, nesting resources, cover, and fruit and floral resources. Large native forest patches function as biodiversity hubs, protecting more urban- sensitive species from urban stressors, and even non-native trees can provide structure or food that benefits native wildlife.
Increased tree canopy cover has been associated with increased prevalence of asthma and allergens although results are mixed. It has been linked to gentrification, so strong housing policies should accompany greening. Trees preferred for human benefits may be exotic species that do not provide the same biodiversity benefits as natives.
Shade heavily used areas, including transit stops and active transportation corridors. Plant deciduous trees along the south and west side of buildings to reduce summer heat.
Soil quality, including physical composition, nutrient structure, acidity, level of compaction, and porosity also strongly affects the health of urban forests. Match tree selection to the available soil volume and quality to support healthy trees.
Consider desired functions and site characteristics. Use native trees where possible, and target locally appropriate levels of diversity. Evaluate potential disservices, including high pollen production, susceptibility to disease, and maintenance issues.
In arid regions, weigh the benefits of tree planting against the increased water use. In cities where trees were not present historically, identify near-native and drought-tolerant trees where possible.
Consider adding features that encourage contemplation and calmness, including small paths, quiet spaces, and benches.