Browsing by Author "Wurster, Frederic C."

Now showing 1 - 5 of 5
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    Hydrologic-based modelling of burn depth potentials in degraded peat soils
    Link, Nicholas T.; McLaughlin, Daniel L.; Stewart, Ryan D.; Strahm, Brian D.; Varner, J. Morgan; Word, Clayton S.; Wurster, Frederic C. (Wiley, 2023-01)
    Peatland drainage may degrade system resilience to high intensity, soil-consuming fires. Peat soil fires are unique in that they can smoulder vertically through the soil column, with a multitude of consequences including large carbon emissions, altered hydrology, and dramatic shifts in vegetation communities. In this work we developed and verified a new method to model peat burn depths with readily available water level and peat hydraulic property data at the Great Dismal Swamp National Wildlife Refuge (VA and NC, USA). To model peat burn depths across 11 sites in the Great Dismal Swamp National Wildlife Refuge we combined water table time series data and soil moisture release curves, developed at multiple depths, with moisture-to-ignition thresholds. A subset of the results from this empirical modelling approach of peat burn depth severity were compared against those made using a mechanistic model of soil moisture, HYDRUS 1-D. By comparing modelled burn depth potentials between these two approaches for a range of peats, we confirmed that our simpler, water table-based approach had similar performance to HYDRUS 1-D in drained and degraded peats, like those found in the Great Dismal Swamp National Wildlife Refuge. A comparative analysis of modelled burn depths across our study site found that water table position and peat water holding capacity were the key governing controls on burn depth potential. Our findings suggest that drainage weakens both short- and long-term controls on peat burn depths by reducing soil moisture and by decreasing peat water holding capacity. This new approach offers land managers with an additional tool for assessing risk while offering insight into the drivers of peatland wildfire severity.
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    Linking ecosystem function and hydrologic regime to inform restoration of a forested peatland
    Schulte, Morgan L.; McLaughlin, Daniel L.; Wurster, Frederic C.; Balentine, Karen; Speiran, Gary K.; Aust, W. Michael; Stewart, Ryan D.; Varner, J. Morgan; Jones, C. Nathan (2019-03-01)
    Drainage is a globally common disturbance in forested peatlands that impacts peat soils, forest communities, and associated ecosystem functions, calling for informed hydrologic restoration strategies. The Great Dismal Swamp (GDS), located in Virginia and North Carolina, U.S.A., has been altered since colonial times, particularly by extensive ditch networks installed to lower water levels and facilitate timber harvests. Consequently, peat decomposition rates have accelerated, and red maple has become the dominant tree species, reducing the historical mosaic of bald cypress, Atlantic white-cedar, and pocosin stands. Recent repair and installation of water control structures aim to control drainage and, in doing so, enhance forest community composition and preserve peat depths. To help inform these actions, we established five transects of 15 plots each (75 plots total) along a hydrologic gradient where we measured continuous water levels and ecosystem attributes, including peat depths, microtopography, and forest composition and structure. We found significant differences among transects, with wetter sites having thicker peat, lower red maple importance, greater tree density, and higher overall stand richness. Plot-level analyses comported with these trends, clearly grouping plots by transects (via nonmetric multidimensional scaling) and resulting in significant correlations between specific hydrologic metrics and ecosystem attributes. Our findings highlight hydrologic controls on soil carbon storage, forest structure, and maple dominance, with implications for large-scale hydrologic restoration at GDS and in other degraded forested peatlands more broadly.
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    Peatland drainage alters soil structure and water retention properties: Implications for ecosystem function and management
    Word, Clayton S.; McLaughlin, Daniel L.; Strahm, Brian D.; Stewart, Ryan D.; Varner, J. Morgan; Wurster, Frederic C.; Amestoy, Trevor J.; Link, Nicholas T. (Wiley, 2022-03)
    Peatland functions (e.g., carbon sequestration and flora diversity) are largely driven by soil moisture dynamics and thus dependent on interactions between hydrologic regimes and organic soil properties. Understanding these interactions is particularly important in drained peatlands, where drier conditions may alter soil properties with feedbacks to soil water retention and associated ecosystem functions. In this work, we focused on the Great Dismal Swamp (GDS) in Virginia, USA, a historically drained, temperate peatland with ongoing hydrologic restoration efforts. Two distinct soil layers varying in thickness exist at GDS: an upper layer with subangular blocky structure thought to be a result of past drainage, and a sapric lower layer with a massive structure more representative of an undisturbed state. To understand the occurrence and consequences of these distinct layers, we used continuous water table data and analysed soil physical and hydraulic properties to characterize soil profiles at 16 locations. We found significant differences between layer properties, where upper layers had lower fibre and organic matter contents and higher bulk densities. Further, moisture release curves demonstrated lower water retention in upper layers compared with lower layers and key differences in pore structure, with upper layers having higher macroporosity. Upper layers varied in thickness across sampling locations (similar to 0.30 to 1.0 m) with a transition to lower soil layers typically occurring at depths below contemporary water level observations, suggesting that the upper layer may be a result of historical drainage and deeper water table conditions. Yet, upper layers with more frequent saturation exhibited higher water retention and lower macroporosity compared with drier upper layers, thus indicating potential recovery following re-wetting efforts. These findings highlight how past drainage influences soil properties and water retention, with important implications for current management objectives at GDS and other drained peatland systems.
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    Red maple dominance and community homogenization in a disturbed forested wetland
    Ludwig, Raymond F.; McLaughlin, Daniel L.; Wurster, Frederic C. (2021-06-09)
    Homogenization of forest stands with generalist species is a hallmark of past disturbance and characterizes the Great Dismal Swamp (GDS), a forested wetland in the Atlantic Coastal Plain. Once a mosaic of wetland communities, disturbances (e.g., timber harvesting and ditching) have resulted in altered hydrologic regimes and forested communities. In response, hydrologic restoration and forest management aim to enhance community composition and function. To inform these efforts, we investigated forest communities and their associations with hydrologic regimes at 79 monitoring plots across GDS, where we collected data on vegetation composition and structure, hydrologic indicators, and soil properties. Our results demonstrate that red maple (Acer rubrum) is the dominant species across GDS, where red maple importance is negatively correlated with stand density, richness, and diversity. A hierarchical cluster analysis revealed four distinct community types: Swamp Tupelo-Maple (ST-M), Maple-Holly (M-H), Sweetgum-Maple (SG-M), and Maple (M). Despite ubiquitous presence of red maple in these communities, significant differences in tree composition and structure were found; however, this variation rarely extended to other growth forms. Although water level estimates (via model simulations and high-water marks) failed to explain vegetation differences, soil properties indicative of wetness regimes suggest that communities exist along a hydrologic gradient. The ST-M community likely exists on wetter sites, whereas SG-M communities occur at drier locations. More maple-dominated communities (M and M-H; 68% of plots) likely occur across broader hydrologic gradients, explaining their widespread occurrence. These findings point to potential drivers of forested communities, but additional characterization of hydrology coupled with continued vegetation monitoring are needed to adaptively conduct hydrologic restoration efforts.
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    Short- and long-term hydrologic controls on smouldering fire in wetland soils
    Schulte, Morgan L.; McLaughlin, Daniel L.; Wurster, Frederic C.; Varner, J. Morgan; Stewart, Ryan D.; Aust, W. Michael; Jones, C. Nathan; Gile, Bridget (2019-02-21)
    Smouldering fire vulnerability in organic-rich, wetland soils is regulated by hydrologic regimes over short (by antecedent wetness) and long (through influences on soil properties) timescales. An integrative understanding of these controls is needed to inform fire predictions and hydrologic management to reduce fire vulnerability. The Great Dismal Swamp, a drained peatland (Virginia and North Carolina, USA), recently experienced large wildfires, motivating hydrologic restoration efforts. To inform those efforts, we combined continuous water levels, soil properties, moisture holding capacity and smouldering probability at four sites along a hydrologic gradient. For each site, we estimated gravimetric soil moisture content associated with a 50% smouldering probability (soil moisture smoulder threshold) and the water tension required to create this moisture threshold (tension smoulder threshold). Soil properties influenced both thresholds. Soils with lower bulk density smouldered at higher moisture content but also had higher moisture holding capacity, indicating that higher tensions (e.g. deeper water tables) are required to reach smouldering thresholds. By combining thresholds with water level data, we assessed smouldering vulnerability over time, providing a framework to guide fire prediction and hydrologic restoration. This work is among the first to integrate soil moisture thresholds, moisture holding capacities and water level dynamics to explore spatiotemporal variation in smouldering fire vulnerability.