Forest fragmentation is a ubiquitous consequence of anthropogenic land-use change, yet its effects on ecosystem processes and biogenic carbon (C) cycling remain unclear, especially belowground. Forest edges, or the boundary of forest and non-forest land cover, experience altered environmental conditions that affect soil biogeochemical cycling and microbial communities. Urbanization can further alter forest soil dynamics and may interact with perturbations at the forest edge in complex, nonlinear ways. Though soils comprise over 40 % of the global forest C sink, the net effects of interacting global change drivers (e.g., rising temperatures, fragmentation, urbanization) are largely unknown, introducing large uncertainties into estimates of soil C fluxes and our understanding of soil ecology. I co-designed and implemented an observational field campaign of forest edges along an urbanization gradient in Massachusetts to characterize soil C cycling and its drivers from the forest edge to the interior. I use field measurements of soil temperature, moisture and C efflux as CO2, or soil respiration, to find diverging trends in soil C losses at urban and rural forest edges. I find that urban soil respiration rates are less sensitive to rising temperatures than rural soils and that urban edges are even less sensitive than their interior counterparts. I then perform a holistic characterization of soil properties and microbial activity to explore the effects of multiple, simultaneous environmental perturbations on forest edge soils. I report that soil C content does not reflect diverging trends in soil C efflux between rural and urban sites and, instead, is generally lower at the forest edge, suggesting a decoupling between edge soil C pools and fluxes. I also report that soil properties often mediated by human activity, such as pH, temperature, and trace element concentrations, broadly predict soil C dynamics from edge to interior across the urbanization gradient. Finally, I conduct a meta-analysis of published studies on forest edge soil C cycling and its drivers and interpret the findings through a lens of broader global change. I demonstrate that soil conditions converge at the forest edge across the globe, where soils are hotter, drier, and less acidic than the forest interior. I find limited investigation of soil C fluxes and substantial variability in edge soil C stocks, and I conclude that forest edges are not direct analogs for global change experiments. My dissertation demonstrates that soil C cycling is significantly altered by both forest fragmentation and urbanization. I highlight the need for further study both in situ at the forest edge and through multi-factor manipulation experiments to improve our understanding of an increasingly fragmented and urbanized forest landscape.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/48473 |
| Date | 23 March 2024 |
| Creators | Garvey, Sarah Marie |
| Contributors | Hutyra, Lucy R. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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