Total C and N Pools and Fluxes Vary with Time, Soil Temperature, and Moisture Along an Elevation, Precipitation, and Vegetation Gradient in Southern Appalachian Forests

Knoepp, Jennifer D.; See, Craig R.; Vose, James M.; Miniat, Chelcy Ford; Clark, James S.

doi:10.1007/s10021-018-0244-2

Cited by 26 publications

(21 citation statements)

References 99 publications

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“…Soils are relatively uniform, described as coarse sandyloam Inceptisols and Ultisols, typically residual with colluvial material in the coves, and areas of deeper, more organic rich soils in toe slope positions (Knoepp and Swank, 1998;Knoepp et al, 2018). Although the research was conducted at five reference watersheds (WS02, WS14, WS18, WS27, and WS36 -3 lowand 2 high-elevation), due to limitations on data availability and access all five watersheds were used for remote sensing analyses; three watersheds for hydrologic analyses (WS14, WS18, and WS27); and one watershed (WS18) for detailed analyses of vegetation growth and sap flow ( Table 1).…”

Section: Study Sitementioning

confidence: 99%

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Climate Change May Increase the Drought Stress of Mesophytic Trees Downslope With Ongoing Forest Mesophication Under a History of Fire Suppression

Hwang

Band

Miniat

et al. 2020

Front. For. Glob. Change

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In mountainous headwater catchments, downslope flow of subsurface water could buffer downslope forest communities from soil moisture stress during drought. Here we investigated changes in landscape-scale vegetation patterns at five forested headwater catchments in the Coweeta Hydrologic Laboratory in the southern Appalachians. We used a ca. 30-year Landsat Thematic Mapper (TM) image record of normalized difference vegetation index (NDVI), spanning a period of recorded warming since the mid-1970. We then, related spatial and temporal canopy patterns to seasonal water balance, streamflow recession behavior, and low flow dynamics from the longterm hydrologic records. All hydrologic metrics indicated increasing evapotranspiration, decreasing streamflow given precipitation, and potentially decreasing downslope subsidy at the watershed scale over time, especially during low-flow periods. Contrary to expectations, leaf area index (LAI) and basal area increased more upslope compared to downslope over time, coincident with warming. Trends in the ratio of NDVI in upslope and downslope topographic positions were also supported by long-term tree basal area increment, litterfall, and sap flux data in one of the reference watersheds. Mesophytic trees downslope appeared to respond more to frequent droughts and experience lower growth than xerophytic trees upslope, closely mediated by the isohydric/anisohydric continuum along hydrologic flow paths. Considering ongoing forest "mesophication" under a history of fire suppression across the eastern United States deciduous forests, this study suggests that mesophytic trees downslope may be more vulnerable than xerophytic trees upslope under ongoing climate change due to an apparent dependence on upslope water subsidy.

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Section: Study Sitementioning

confidence: 99%

“…Lastly, the ratios of leaf area downslope to upslope and watershedscale standard deviations were computed each year to compare with the catchment-scale vegetation metrics above. More details on plot establishment, basal area, and litterfall sampling can be found in Knoepp et al (2018).…”

Section: Long-term Tree Basal Area and Leaf Litter Datamentioning

confidence: 99%

Climate Change May Increase the Drought Stress of Mesophytic Trees Downslope With Ongoing Forest Mesophication Under a History of Fire Suppression

Hwang

Band

Miniat

et al. 2020

Front. For. Glob. Change

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“…Table 1 contains more detailed climatic, vegetation and soils information. [15], and mean annual temperature and precipitation data are from [16].…”

Section: Site Descriptionmentioning

confidence: 99%

“…In the southern Appalachian Mountains, net N mineralization and nitrification rates are lower in mixed-oak-pine and low-elevation mixed-oak forest community types, relative to cove hardwood and northern hardwood forest communities [14,15]. Across sites, Knoepp and colleagues [14,16] found greater leaf litter inputs in forest types with greater rates of soil N cycling but not necessarily greater annual net primary productivity or rates of aboveground biomass accumulation. All sites had significant interactions between soil temperature and moisture affecting N cycling rates [17] and leaf N flux (i.e., greater N availability) [16].…”

Section: Introductionmentioning

confidence: 98%

“…Across sites, Knoepp and colleagues [14,16] found greater leaf litter inputs in forest types with greater rates of soil N cycling but not necessarily greater annual net primary productivity or rates of aboveground biomass accumulation. All sites had significant interactions between soil temperature and moisture affecting N cycling rates [17] and leaf N flux (i.e., greater N availability) [16]. A model by Bouwman et al [18] estimated that soil denitrification (N 2 and N 2 O) rates may account for 25% of all global gaseous N inputs (~90 Tg N y −1 ).…”

Section: Introductionmentioning

confidence: 99%

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Well-Aerated Southern Appalachian Forest Soils Demonstrate Significant Potential for Gaseous Nitrogen Loss

Baas

Knoepp

Mohan

2019

Forests

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Understanding the dominant soil nitrogen (N) cycling processes in southern Appalachian forests is crucial for predicting ecosystem responses to changing N deposition and climate. The role of anaerobic nitrogen cycling processes in well-aerated soils has long been questioned, and recent N cycling research suggests it needs to be re-evaluated. We assessed gross and potential rates of soil N cycling processes, including mineralization, nitrification, denitrification, nitrifier denitrification, and dissimilatory nitrate reduction to ammonium (DNRA) in sites representing a vegetation and elevation gradient in the U.S. Department of Agriculture (USDA) Forest Service Experimental Forest, Coweeta Hydrologic Laboratory in southwestern North Carolina, USA. N cycling processes varied among sites, with gross mineralization and nitrification being greatest in high-elevation northern hardwood forests. Gaseous N losses via nitrifier denitrification were common in all ecosystems but were greatest in northern hardwood. Ecosystem N retention via DNRA (nitrification-produced NO3 reduced to NH4) ranged from 2% to 20% of the total nitrification and was highest in the mixed-oak forest. Our results suggest the potential for gaseous N losses through anaerobic processes (nitrifier denitrification) are prevalent in well-aerated forest soils and may play a key role in ecosystem N cycling.

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Characteristics and drivers of vegetation productivity sensitivity to increasing CO₂ at Northern Middle and High Latitudes

Chai,

2024

Ecology and Evolution

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Understanding and accurately predicting how the sensitivity of terrestrial vegetation productivity to rising atmospheric CO2 concentration (β) is crucial for assessing carbon sink dynamics. However, the temporal characteristics and driving mechanisms of β remain uncertain. Here, observational and CMIP6 modeling evidence suggest a decreasing trend in β at the Northern Middle and High Latitudes during the historical period of 1982–2015 (−0.082 ± 0.005% 100 ppm−1 year−1). This decreasing trend is projected to persist until the end of the 21st century (−0.082 ± 0.005% 100 ppm−1 year−1 under SSP370 and −0.166 ± 0.006% 100 ppm−1 year−1 under SSP585). The declining β indicates a weakening capacity of vegetation to mitigate warming climates, posing challenges for achieving the temperature goals of the Paris Agreement. The rise in vapor pressure deficit (VPD), that triggers stomata closure and weakens photosynthesis, is considered as the dominated factor contributing to the historical and future decline in β, accounting for 62.3%–75.2% of the effect. Nutrient availability and water availability contribute 15.7%–21.4% and 8.5%–16.3%, respectively. These findings underscore the significant role of VPD in shaping terrestrial carbon sink dynamics, an aspect that is currently insufficiently considered in many climate and ecological models.

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Total C and N Pools and Fluxes Vary with Time, Soil Temperature, and Moisture Along an Elevation, Precipitation, and Vegetation Gradient in Southern Appalachian Forests

Cited by 26 publications

References 99 publications

Climate Change May Increase the Drought Stress of Mesophytic Trees Downslope With Ongoing Forest Mesophication Under a History of Fire Suppression

Climate Change May Increase the Drought Stress of Mesophytic Trees Downslope With Ongoing Forest Mesophication Under a History of Fire Suppression

Well-Aerated Southern Appalachian Forest Soils Demonstrate Significant Potential for Gaseous Nitrogen Loss

Characteristics and drivers of vegetation productivity sensitivity to increasing CO₂ at Northern Middle and High Latitudes

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Total C and N Pools and Fluxes Vary with Time, Soil Temperature, and Moisture Along an Elevation, Precipitation, and Vegetation Gradient in Southern Appalachian Forests

Cited by 26 publications

References 99 publications

Climate Change May Increase the Drought Stress of Mesophytic Trees Downslope With Ongoing Forest Mesophication Under a History of Fire Suppression

Climate Change May Increase the Drought Stress of Mesophytic Trees Downslope With Ongoing Forest Mesophication Under a History of Fire Suppression

Well-Aerated Southern Appalachian Forest Soils Demonstrate Significant Potential for Gaseous Nitrogen Loss

Characteristics and drivers of vegetation productivity sensitivity to increasing CO2 at Northern Middle and High Latitudes

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Characteristics and drivers of vegetation productivity sensitivity to increasing CO₂ at Northern Middle and High Latitudes