Aboveground Carbon Storage: We used a combination of field-collected and available remote sensing data to develop a model for measuring the amount of carbon stored in trees within forested areas of the Greenbelt. We acquired LiDAR (light detection and ranging) data of Washtenaw County from 2017 to estimate tree height and volume, and we measured tree species and diameter at three sites located in Washtenaw County to estimate tree biomass using allometric equations from the literature. Using these data sources, we compared the effectiveness of various modeling methods to predict biomass across sites. We found that a Power Law model allowed us to best estimate aboveground carbon storage. We were able to estimate both per-parcel and total aboveground carbon stored in the Ann Arbor Greenbelt, which as of April 2021 totals 32,595,817 kg C, or 119,519 metric tons of CO2. This is equivalent to the annual CO2 emissions of 2,716 average Ann Arbor households, 80,682,715 passenger vehicle miles, or 1,348,245 airline miles. This equates to a value of $6,095,473.15 when using the 2021 EPA social cost of carbon value of $51 per metric ton of CO2.
Belowground Carbon Storage: To estimate the amount of carbon stored in the soil of Greenbelt properties we used available spatial data on soil type together with standards from the literature for calculating carbon stored in the organic matter of soils. We used the National Resources Conservation Service (NRCS) Web Soil Survey to determine which soil types are present in the forested and wetland areas of the Greenbelt District and which characteristics, including horizon depth, bulk density, and organic matter content, are known to be associated with these soil types. Transferring these values into ArcGIS Pro allowed us to provide low, medium, and high estimates of carbon storage for each soil type and develop a model to calculate soil carbon stored at an individual property level. We found that the estimated carbon contained in the uppermost horizon of forested and wetland soils of the Greenbelt properties as of April 2021 totals 50,005,732 kg C, or 183,356 metric tons of CO2. This is equivalent to the annual CO2 emissions of 4,167 average Ann Arbor households, 123,776,564 passenger vehicle miles, or 2,068,363 airline miles. Using the EPA’s 2021 social cost of carbon value, we found that the Greenbelt properties have a value of $9,351,156.96. Agricultural soils were not included in estimates given that soil carbon would depend highly on specific cultivation practices, which are neither constant nor easy to assess.
Water Quality: To evaluate how land protection under the Greenbelt program contributes to water ecosystem services, we compared tools that assess the impact of land conversion on water quality. Based on this review we recommended amendments to existing tools that would improve their applicability to the Greenbelt Program and accessibility for other land conservancies in Southeast Michigan. Specifically, we provided an updated web-based version of the EPA Region 5 Conservation Easement Load Reduction Worksheet and identified the Michigan State University Institute of Water Research’s Great Lakes Watershed Management System (GLWMS) as the optimal tool for future water quality analyses within Washtenaw County. We recommend further collaboration with the Institute of Water Research to expand the spatial scope of its tool to include the Huron River Watershed.