A small imbalance in plant productivity and decomposition accounts for the carbon (C) accumulation capacity of peatlands. As climate changes, the continuity of peatland net C storage relies on rising primary production to offset increasing ecosystem respiration (ER) along with the persistence of older C in waterlogged peat. A lowering in the water table position in peatlands often increases decomposition rates, but concurrent plant community shifts can interactively alter ER and plant productivity responses. The combined effects of water table variation and plant communities on older peat C loss are unknown. We used a full-factorial 1-m3 mesocosm array with vascular plant functional group manipulations (Unmanipulated Control, Sedge only, and Ericaceous only) and water table depth (natural and lowered) treatments to test the effects of plants and water depth on CO2 fluxes, decomposition, and older C loss. We used Δ14 C and δ13 C of ecosystem CO2 respiration, bulk peat, plants, and porewater dissolved inorganic C to construct mixing models partitioning ER among potential sources. We found that the lowered water table treatments were respiring C fixed before the bomb spike (1955) from deep waterlogged peat. Lowered water table Sedge treatments had the oldest dissolved inorganic 14 C signature and the highest proportional peat contribution to ER. Decomposition assays corroborated sustained high rates of decomposition with lowered water tables down to 40 cm below the peat surface. Heterotrophic respiration exceeded plant respiration at the height of the growing season in lowered water table treatments. Rates of gross primary production were only impacted by vegetation, whereas ER was affected by vegetation and water table depth treatments. The decoupling of respiration and primary production with lowered water tables combined with older C losses suggests that climate and land-use-induced changes in peatland hydrology can increase the vulnerability of peatland C stores.
Periodic silvicultural thinnings (23.0, 27.6, 32.1 m 2 ha -1 residual basal area) in a red pine stand growing on a sandy soil in north-central Minnesota over a 57-yr period increased soil compaction as the intensity of the thinning treatment increased. Of the three different methods used to measure soil compaction (bulk density, penetration resistance, and saturated hydraulic conductivity), saturated hydraulic conductivity was the most sensitive, decreasing by 60% in the 23.0 m 2 ha -1 basal area thinning treatment, as compared with the uncut control. Soil bulk density measurements were more variable, but generally increased with increased thinning intensity. Few differences in soil penetration resistance were found among the three thinning treatments. In contrast, no evidence of soil compaction was detected in a northern hardwoods stand growing on a rocky loam soil in north-central Wisconsin that had three thinning treatments (13.8, 17.2, 20.6 m 2 ha -1 residual basal area), a two- stage shelterwood harvest, and a 20-cm-diameter limit cut over a 50-yr period. With the increased demand for forest products, fuel reduction operations in high fire-risk stands, and biomass removal for energy production, more information is needed on the impact of multiple stand entries on soil compaction, and if compaction occurs, whether it will affect long-term soil productivity. Key words: Soil physical properties, bulk density, soil penetration resistance, hydraulic conductivity
The Marcell Experimental Forest (MEF) was established to study the effects of forest management on watershed dynamics in upland-peatland landscapes. We are not aware of any other research location that has the depth and breadth of data from these landscapes (Chapter 2). Findings from 50 years of research constitute a foundational knowledge of the hydrology and biogeochemistry of peatland watersheds (Table 3.1). In this chapter, we discuss what historically and currently drives our research program, the importance of networks in our research portfolio, summarize our past and current research, assess what expert panels anticipate are important future research topics, and align our expectations of future research at the MEF.
This report documents the role of the USDA Forest Service and their collaborators (SRTC, SREL, and several universities) in wetlands monitoring and research on the Savannah River Site. This report describes the rationales, methods, and results (when available) of these studies and summarizes and integrates the available information through 1996.
