“Sealed in San José:” Paving of front yards diminishes urban forest resource and benefits in low-density residential neighborhoods

Abstract

Paving over of front yards (soil sealing) reduces the environmental and social benefits of front yards and trees. There is substantial documentation that soil sealing has reduced ecosystem services in Europe, but studies about this phenomenon in the United States are limited. We assessed soil sealing across a sample of over 25,000 parcels in San José (California) in order 1) to quantify the potential loss of ecosystem services associated with soil sealing, and 2) to find associations between soil sealing and demographic, socio-economic and parcel characteristics. Our study found that soil sealing was common: 5 % of all lots included soil sealing beyond that which was originally installed, covering on those lots an additional 11 % of the previously-pervious surface, and leading to substantial reductions in ecosystem services. Extrapolated over the entire city, the sealed soil (>30 ha) precludes the planting of nearly 8000 trees, and generates annually an additional 139,000 m3 of runoff polluting the local waterways with, among others, an added 5.5 metric tons of suspended solids. Most demographic variables were not associated with soil sealing, but income was negatively correlated (areas of higher income had lower rates of sealing). Our results advance the understanding of the magnitude and impacts of the soil sealing problem in the USA, and we briefly suggest steps for policy and practice to reduce the extent and impacts of soil paving in low-density residential neighborhoods.