Tree Canopy Cover Response to Land Development Policies in Fairfax County

Abstract

Urban tree canopy cover is important because it mitigates negative impacts of urbanization such as urban heat and stormwater. Land development leads to canopy loss through tree removal, but some localities have regulations in place that require trees to be retained or replanted during development. The goal of these regulations is to preserve tree cover. Since 2009, Fairfax County, Virginia has had an ordinance that requires parcels to reach a certain amount of canopy 10 years post-development. However, it was unknown if the requirements of this ordinance were being met. To investigate this issue, we determined which developed parcels met their required canopy using remotely-sensed tree canopy cover data from 2021. We then conducted an additional analysis on a sample of developed parcels using their site plans to compare the canopy proposed by developers to the measured canopy from the geospatial data. These results were then compared to potential predictors of ordinance compliance to determine if there were certain attributes of a parcel that may drive ordinance compliance. Of all 482 parcels in Fairfax County that were developed from 2009 to 2011, 79.46% met their canopy requirements by 2021. For the sample of 151 developed parcels, 70% reached the proposed amount of canopy by 2021. The results suggest that Fairfax County's ordinance is promoting preservation of tree canopy cover in developed areas as intended. Zoning type, amount of canopy required, parcel size, impervious cover, and pre-existing canopy were all found to have a significant relationship with ordinance compliance. These findings could improve the understanding of the efficacy of tree ordinances in other localities.