OOS 10-3 - Modeling the potential contributions of urban agroforestry to a more circular economy in Rhode Island, USA

Background/Question/Methods
Urban agroforestry (UAF) potentially provides higher levels of regulating services than annual urban agriculture. When well designed, some UAF systems, e.g., food forests, may also be psychologically preferred because of higher levels of planned and associated biodiversity and vegetative complexity. However, integration of UAF systems into the fabric and metabolism of the city requires greater planning and commitment because of their complexity and longevity. They may also be less productive than annual systems. In this study, we modeled the production and nutrient-cycling potential and other ecosystem services of a simple fruit and nut crop assemblage for nine municipalities in Rhode Island, the second most densely populated state in the USA. We used LiDAR and other data sources and the area solar radiation tool in ArcGIS Pro to identify areas suitable for UAF. Yield data and relative proportions of planting area for each crop in the assemblage—apple, peach, pear, highbush blueberry, raspberry, and strawberry—were derived from USDA data for New England, while nutrient demands of each crop were based on Cooperative Extension publications. Hybrid hazelnuts—not commonly grown in Rhode Island—were added to the assemblage for dietary enhancement.

Results/Conclusions
We identified 1860 ha of residential, institutional, and vacant land meeting our criteria for UAF: > 75% maximum midseason solar insolation, unsealed surface, existing vegetation and structures < 1.5 m in height, area > 9.3 m², and planting area width > 3 m to accommodate minimum tree size. Most of this land—1550 ha—is residential. Based on EAT-Lancet Planetary Health Diet recommendations and model assumptions,1860 ha of UAF could meet the annual fruit needs of almost 262,000 adults and nut needs of almost 46,000, or 56% and 10%, respectively, of the study area’s adult population. System productivity could be further increased by inclusion of food crops under the tree canopy, but little data is available for modeling the impact of shading on crop yields. Comparison of crop nutrient needs and potential recoverable nutrients from municipal solid waste generated by the study area indicates the latter could more than satisfy the former. Additional benefits of UAF were estimated, including carbon sequestration and stormwater and urban heat island mitigation. While study results indicate UAF could make substantial contributions to the circularity of the urban economy, expanding its practice will require considerable investment in material and technical support, particularly at the residential scale.