Modeling Carbon Sequestration in the U.S. Residential Landscape

Abstract

The role of terrestrial carbon (C) sequestration in urban areas is an issue of increasing interest. Therefore, a model was developed to evaluate the potential of sequestration in U.S. residential landscapes. The model contrasted C sequestered by trees, shrubs, lawns, and a forest. The first objective of this model is to document the typical urban landscape in terms of lawn area, number of trees and shrubs, area of landscape and garden beds, hard surfaces, and buildings. The second objective is to estimate the annual rate of C sequestration of the residential landscape based on the percentage of lawns, trees, and shrubs. Urbanized land occupies approximately 40.6 million hectares (Mha) with an average of 41% of this land under residential use. Tree, shrub, and lawn C sequestration rates were estimated based on the typical US residential lot size of 2,000 m². A typical US home is 93 m² with a 2-car garage or carport size of 38 m² and a deck or patio of 38 m². The house is generally sited in the middle of the lot, with a driveway of 168 m² and a sidewalk of 122 m² along the front of the lot, leaving a landscape area of 1,541 m² Two landscape regimes were modeled, the first involving a minimal area with one landscape bed in the front of the house 13 m long containing 5–10 shrubs approximately 0.6–1.2 m in length and width, 2 trees, and a minimally managed lawn. The second model had the maximum area with several landscape beds 43 m long surrounding the perimeter of the house containing 17–35 shrubs approximately 0.6–1.2 m in length and width, 6 trees, and a highly maintained lawn. The total or gross C sequestration rate is 3.4–5.9 kg C tree⁻¹ year⁻¹ and 0.07–0.23 kg C shrub⁻¹ year⁻¹. The C sequestration rate for lawn is 254–2,043 kg C ha⁻¹ year⁻¹ based on the models described above. A minimal landscape sequesters an average of 25–116 kg C ha⁻¹ year⁻¹ (39–178 kg C yard⁻¹ year⁻¹). Based on the model, residential lawns and landscapes fall within the same range of CO₂ sequestration as a forest land. In a minimal landscape, approximately 8.6% of the C is sequestered by trees, 1.3% by shrubs, and 90.1% by the lawn. The maximum landscape model estimates C sequestration at an average rate of 42–191 kg C ha⁻¹ year⁻¹ (65–294 kg C yard⁻¹ year⁻¹) comparising 15.5% by trees, 2.7% by shrubs, and 81.8% by the lawn.