Soils store more carbon (C) than the atmosphere and terrestrial plants combined. Humans alter soil ecosystem C pools from the urban core to rural periphery. Urban and suburban land uses, such as yards and parks, often store more soil C than undisturbed lands, while the effect of exurban land use on soil C storage is lesser known. How do soil C pools differ across residential exurban yard-field-forest land use gradients? Does varying intensity of yard management affect soil C pools? Is soil solution dissolved organic carbon (DOC) transport related to differences in soil C pools?
In the Upper Connecticut River Valley, VT and NH, yards (n = 19) were selected adjacent to mown fields (n = 8) and second-growth forests (n = 7) to control for land use history. Participating residents were interviewed about their property history and management. Yards were categorized as either intensively (n = 9; mowing, clipping removal, irrigation and fertilizing) or non-intensively (n = 10; mowing as needed) managed. Three soil cores were extracted to 60-cm depth within land uses, and analyzed for C, N, pH, bulk density, and moisture content by upper (0-10 cm & 10-20 cm) and deep soil (20-40 cm & 40-60 cm). Across one land use gradient site, soil solution DOC concentrations were monitored in upper and deep soil.
Yards stored less soil carbon to 60-cm depth (10.43 kg C m-2) than forest (13.28 kg C m-2) and field soils (12.08 kg C m-2). Across six land use clusters (LUC), defined by a yard-field-forest gradient, land use and depth explained soil C pools in a linear mixed effects model, with LUC as a random effect. Yard soil C pools, averaged over depths, were lower than adjacent forests (p < 0.05). Field (1.32 g cm-3) and yard (1.21 g cm-3) soil bulk density, averaged over depths, were significantly greater than forest soils (1.04 g cm-3). The interaction of yard management (mean 26 y.) and house age (mean 99 y.) explained yard soil C pools to 60-cm depth. Preliminary soil solution data suggested higher DOC concentrations in yard and field deep soil relative to forest. Land-use conversion, a legacy of soil disturbance, limits the magnitude of soil C pools. Exurban land-use change alters soil carbon pools and the function of soils to provide essential ecosystem services.