Jennifer Knoepp - Academia.edu (original) (raw)
Papers by Jennifer Knoepp
Alms and scope. Forest Ecology and Management publishes scientific articles concerned with forest... more Alms and scope. Forest Ecology and Management publishes scientific articles concerned with forest management and conservation, and in particular the application of biological, ecological and social knowledge to the management of man-made and natural forests. The scope of the journal includes all forest ecosystems of the world. A refereeing process ensures the quality and international interest of the manuscripts accepted for publication. The journal aims to encourage communication between scientists in disparate fields who share a common interest in ecology and natural-resource management, and to bridge the gap between research workers and forest managers in the field to the benefit of both. The journal should be of interest to research workers, managers and policy makers in forestry, natural resources, ecological conservation and related fields.
Journal of Environmental Quality, 2008
We predicted the eff ects of sulfate (SO 4 ) deposition on wilderness areas designated as Class I... more We predicted the eff ects of sulfate (SO 4 ) deposition on wilderness areas designated as Class I air quality areas in western North Carolina using a nutrient cycling model (NuCM). We used three S deposition simulations: current, 50% decrease, and 100% increase. We measured vegetation, forest fl oor, and root biomass and collected soil, soil solution, and stream water samples for chemical analyses. We used the closest climate stations and atmospheric deposition stations to parameterize NuCM. Th e areas were: Joyce Kilmer (JK), Shining Rock (SR), and Linville Gorge (LG). Th ey diff er in soil acidity and nutrients, and soil solution and stream chemistry. Shining Rock and LG have lower soil solution base cation and higher acidic ion concentrations than JK. For SR and LG, the soil solution Ca/Al molar ratios are currently 0.3 in the rooting zone (A horizon), indicating Al toxicity. At SR, the simulated Ca/Al ratio increased to slightly above 1.5 after the 30-yr simulation regardless of S deposition reduction. At LG, Ca/Al ratios ranged from 1.6 to 2.4 toward the end of the simulation period, the 100% increase scenario had the lower value. Low Ca/Al ratios suggest that forests at SR and LG are signifi cantly stressed under current conditions. Our results also suggest that SO 4 retention is low, perhaps contributing to their high degree of acidifi cation. Th eir soils are acidic, low in weatherable minerals, and even with large reductions in SO 4 and associated acid deposition, it may take decades before these systems recover from depletion of exchangeable Ca, Mg, and K.
Southern Appalachian forests are undergoing considerable change due to altered disturbance regime... more Southern Appalachian forests are undergoing considerable change due to altered disturbance regimes. For example, fire exclusion has had a major impact on the structure and function of pine-hardwood ecosystems. Recently, fire has been prescribed for a variety of applications: 1) stand-replacement in the form of a mimicked wildfire, 2) site-preparation as part of a fell-and-burn prescription, and 3) understory burning
The mixed oak-pine ecosystems in the southern Appalachians are in decline because of a combinatio... more The mixed oak-pine ecosystems in the southern Appalachians are in decline because of a combination of drought and southern pine-beetle infestation. A commonly applied prescription for restoration of these degraded sites has been to fell all vegetation, allow it to dry, and conduct a site-preparation burn. However, there is little information on the mid- and long-term influences of this prescription
Lab Rd, Otto, NC 28763). Effects of prescribed fire in mixed oak forests of the southern Appalach... more Lab Rd, Otto, NC 28763). Effects of prescribed fire in mixed oak forests of the southern Appalachians: forest floor, soil, and soil solution nitrogen responses. J. Torrey Bot. Soc. 136: 000-000. 2009-We examined nutrient cycling responses to prescribed fire on three sub-mesic, mixed-oak sites located in the Blue Ridge Physiographic province of the southern Appalachian Mountains: Alarka Laurel Branch (AL), Robin Branch (RB), and Roach Mill Branch (RM). Each study site was located within a sub-watershed that drained a first order stream. Our objective was to quantify the effects of prescribed burning on forest floor mass, nitrogen and carbon pools; and soil and soil water available nitrogen. Each site included a burned and unburned control area; both burned and control areas were sampled before and after burning. Within each plot, we sampled forest floor mass, carbon and nitrogen, soil and soil solution nitrate (NO3-N) and ammonium (NH4-N) concentrations before and after the prescribed burns. All prescribed fires were conducted in the dormant season and were low to moderate intensity. All sites lost a significant amount of forest floor mass due to burning; 82 to 91% of the Oi layer and 26 to 46% of the Oe + Oa layer. Soil NH4-N concentrations increased in surface soils (0-5 cm) only, immediately after burning, but return to pre-burn levels by mid-summer. Burning had no measurable effect on soil solution inorganic nitrogen concentrations. Low levels of solution NO3-N and NH4-N after burning and no change in stream NOi-N concentrations indicated that no inorganic nitrogen was lost from these sites.
Information is lacking on ecosystem effects of understory burning in mesic mixed-oak (Quercus spp... more Information is lacking on ecosystem effects of understory burning in mesic mixed-oak (Quercus spp.) forests of the southern Appalachians. Native Americans used periodic fires in these forests for driving game and opening the forest. In April 1998, we conducted a low- to moderate-intensity fire in a cove-hardwood forest in the Nantahala National Forest, western North Carolina. In March 1998, before
Environmental Pollution, 2002
The effects of harvest intensity (sawlog, SAW; whole tree, WTH; and complete tree, CTH) on biomas... more The effects of harvest intensity (sawlog, SAW; whole tree, WTH; and complete tree, CTH) on biomass and soil C were studied in four forested sites in the southeastern US (mixed deciduous forests at Oak Ridge, TN and Coweeta, NC; Pinus taeda at Clemson, SC; and P. eliottii at Bradford, FL). In general, harvesting had no lasting effects on soil C.
International Journal of Environmental Studies, 2008
GENV_A_286400.sg m We studied nitrogen (N) cycling pools and processes across vegetation and elev... more GENV_A_286400.sg m We studied nitrogen (N) cycling pools and processes across vegetation and elevation gradients in the southern Appalachian Mountains in SE USA. Measurements included bulk deposition input, water- shed export, throughfall fluxes, litterfall, soil N pools and processes, and soil solution N. N deposition increased with elevation and ranged from 9.5 to 12.4 kg ha −1 yr−1. In all
Soil Science Society of America Journal, 1994
Assessing potential long-term forest productivity requires identification of the processes regula... more Assessing potential long-term forest productivity requires identification of the processes regulating chemical changes in forest soils. We resampled the litter layer and upper two mineral soil horizons, A and AB/BA, in two aggrading southern Appalachian watersheds 20 yr after an earlier sampling. Soils from a mixed-hardwood watershed exhibited a small but significant decrease in soil pH. Extractable base cation content declined substantially in both mineral horizons. For example, Ca 2+ levels in the A horizon fell from 236 kg ha" 1 in 1970 to 80 kg ha" 1 in 1990. Proportionally, the decline was greatest for Mg 2 " 1 ", which dropped from 111 to 20 kg ha" 1 . A white pine (Pinus strobus L.) plantation was planted in 1956, after clear-felling hardwoods and recutting sprouts for 15 yr. Soil pH and base cation concentrations declined in the A horizon from 1970 to 1990. Soil pH declined from 5.9 to 5.0 and Ca 2+ levels from 534 to 288 kg ha" 1 . Cation content did not change significantly in the AB/BA soil horizon. Nutrient budgets were constructed using these soil and litter data plus existing data on weathering rates, forest productivity, and hydrologic fluxes and associated chemistry. Decreases in soil base cations and soil pH are attributed to leaching and to the sequestration of nutrients in biomass.
Soil Science Society of America Journal, 1995
The existence of several different methods for measuring net N mineralization and nitrification r... more The existence of several different methods for measuring net N mineralization and nitrification rates and indexing N availability has raised questions about the comparability of these methods. We compared in situ covered cores, in situ buried bags, aerobic laboratory incubations, and tension lysimetry on control and treated plots of a prescribed burn experiment in the southern Appalachians. Environmental influences were examined with soil moisture and temperature measurements. All methods detected significant differences in net N mineralization rates between treated and control plots; P = 0.04, 0.007,0.001, and 0.07 for covered cores, buried bags, lab incubations, and lysimeters, respectively. Mean rates of N mineralization during the growing season were similar for the three soil incubation methods. The laboratory incubation of soil from treated plots produced significantly greater potential nitrification rates than the in situ methods. The four methods were not well correlated; this indicates the need for caution when comparing N transformation data derived from different methods. We conclude that the in situ covered core method is superior because it best incorporates site-specific soil temperature and moisture changes into N transformation measurements.
Soil Science Society of America Journal, 1995
Soil Science Society of America Journal, 1997
Changes in surface soil C and N can resuh from forest management practices and may provide an ind... more Changes in surface soil C and N can resuh from forest management practices and may provide an index of impacts on long-term site productivity. Soil C and N were measured over time for five watersheds in the southern Appalachians: two aggrading hardwood forests, one south-and one north-facing, undisturbed since the 1920s; a white pine (Pinus strobus L.) plantation planted in 1956; and two regenerating hardwood forests, a whole-tree harvest in 1980, and a commercial sawlog harvest in 1977. Soils on harvested watersheds were sampled before and for =15 yr after harvest. Surface soil C concentration on the undisturbed watersheds varied significantly among sample years. Concentrations fluctuated on the south-facing and decreased on the north-facing watershed. The pattern for total N was similar. Total N decreased significantly on the north-facing but was stable on the southfacing watershed. In the white pine plantation, C increased while N concentrations decreased during the 20-yr period. Soil C and N concentrations generally declined the first year following whole-tree harvest. Fourteen years after cutting, C remained stable, while N was greater compared with reference watershed soils. The commercial sawlog harvest resulted in large increases in surface soil C and N concentrations immediately after cutting. Carbon levels remained elevated 17 yr following cutting. Our data suggest that the forest management practices examined do not result in long-term decreases in soil C and N. However, the high interannual variation on all watersheds suggests that care must be taken in selecting control sites to determine long-term treatment impacts.
Journal of Environment Quality, 2009
Establishment of riparian buff ers is an eff ective method for reducing nutrient input to streams... more Establishment of riparian buff ers is an eff ective method for reducing nutrient input to streams. However, the underlying biogeochemical processes are not fully understood. Th e objective of this 4-yr study was to examine the eff ects of riparian zone restoration on soil N cycling mechanisms in a mountain pasture previously degraded by cattle. Soil inorganic N pools, fl uxes, and transformation mechanisms were compared across the following experimental treatments: (i) a restored area with vegetation regrowth; (ii) a degraded riparian area with simulated eff ects of continued grazing by compaction, vegetation removal, and nutrient addition (+N); and (iii) a degraded riparian area with simulated compaction and vegetation removal only (-N). Soil solution NO 3 concentrations and fl uxes of inorganic N in overland fl ow were >90% lower in the restored treatment relative to the degraded (+N) treatment. Soil solution NO 3 concentrations decreased more rapidly in the restored treatment relative to the degraded (-N) following cattle (Bos taurus) exclusion. Mineralization and nitrifi cation rates in the restored treatment were similar to the degraded (-N) treatment and, on average, 75% lower than in the degraded (+N) treatment. Nitrogen trace gas fl uxes indicated that restoration increased the relative importance of denitrifi cation, relative to nitrifi cation, as a pathway by which N is diverted from the receiving stream to the atmosphere. Changes in soil nutrient cycling mechanisms following restoration of the degraded riparian zone were primarily driven by cessation of N inputs. Th e recovery rate, however, was infl uenced by the rate of vegetation regrowth.
Frontiers in Ecology and the Environment, 2005
Forest Ecology and Management, 1997
There is increasing concern about the effects of nutrient removal associated with various forest ... more There is increasing concern about the effects of nutrient removal associated with various forest harvesting practices on long-term site productivity. We measured exchangeable soil cation concentration responses to a commercial clearcut sawlog harvest in mixed hardwoods on a 59-ha watershed in the southern Appalachians. Soils were sampled 17 months prior to, and periodically for 17 years after, harvest. Concentrations of Ca, Mg, and K, increased significantly in the 0-10-cm soil layer for 3 years following harvest compared to pre-treatment levels. Concentrations of Mg and K were still significantly above pre-treatment levels 17-20 years following harvest. Calcium concentrations did not change significantly at the 10-30 cm depth, but both Mg and K showed significantly higher concentrations in some post-treatment years. Soils in the adjacent reference watershed showed no significant changes in soil cation concentrations over the same 17-year period. Results indicate that sawlog harvest using cable-yarding techniques on these sites does not adversely impact soil cation concentrations. © 1997 Elsevier Science B.V.
Forest Ecology and Management, 1999
Fine-hardwood ecosystems in the southern Appalachians are in serious decline due to fire exclusio... more Fine-hardwood ecosystems in the southern Appalachians are in serious decline due to fire exclusion and insect infestations. Fire has been advanced as a tool to restore these ecosystems, yet there are few studies evaluating overall ecosystem effects. Our objectives were to evaluate the effects of stand restoration burning on forest floor nitrogen (N) and carbon (C) pools, and soil and stream chemisuy. We measured changes in forest floor (coarse woody debris, small wood, litter, and humus) mass, N, and C; changes in soil chemistry (calcium (Ca), potassium (K), magnesium (Mg), cation exchange capacity (CEC), pH, C, and N); and changes in stream nitrate (NO& Results showed that significant reductions in mass, N, and C occurred only for litter and small wood on the ridge, where N losses were 52.9 kg ha-' for litter and small wood combined. No significant effects were observed on the mid-or lower slope of the treatment watershed. Losses on the ridge are considerably lower than losses which occur with alternative burning treatments used in the region, such as the fell and bum treatment. Soil and stream chemistry showed no response to burning. Spatial heterogeneity @ fire intensity (combustion temperatures ranged from d2->8OO"C) and severity associated with stand replacement burning results in a mosaic of fire effects and considerably less consumption and subsequent nutrient losses. 0 1999 Elsevier Science B.V. All rights reserved.
Forest Ecology and Management, 2004
Understory prescribed burning is being suggested as a viable management tool for restoring degrad... more Understory prescribed burning is being suggested as a viable management tool for restoring degraded oak-pine forest communities in the southern Appalachians yet information is lacking on how this will affect ecosystem processes. Our objectives in this study were to evaluate the watershed scale effects of understory burning on total aboveground biomass, and the carbon and nitrogen pools in coarse woody debris (CWD), forest floor and soils. We also evaluated the effects of burning on three key biogeochemical fluxes; litterfall, soil CO 2 flux and soil net nitrogen mineralization. We found burning significantly reduced understory biomass as well as the carbon and nitrogen pools in CWD, small wood and litter. There was no significant loss of carbon and nitrogen from the fermentation, humus and soil layer probably as the result of low fire intensity. Burning resulted in a total net loss of 55 kg ha À1 nitrogen from the wood and litter layers, which should be easily replaced by future atmospheric deposition. We found a small reduction in soil CO 2 flux immediately following the burn but litterfall and net nitrogen mineralization were not significantly different from controls throughout the growing season following the burn. Overall, the effects of burning on the ecosystem processes we measured were small, suggesting that prescribed burning may be an effective management tool for restoring oak-pine ecosystems in the southern Appalachians. Published by Elsevier B.V.
Forest Ecology and Management, 2005
Soil nutrient concentrations decreased in an aggrading southern Appalachian forest over a 20-year... more Soil nutrient concentrations decreased in an aggrading southern Appalachian forest over a 20-year period. Construction of nutrient budgets showed significant nutrient sequestration aboveground including increased forest floor mass. We hypothesized that the changes in forest floor mass resulted from decreased litter decomposition rates because of decreased litter quality. In 1992 and 1993, we repeated a litter decomposition experiment conducted in 1969 and 1970 to test this hypothesis. In addition, we examined microarthropod populations and functional groups as litter decomposed. For four of the five species tested, firstyear decomposition rates were about the same in both experiments. Initial litter nutrient concentrations of P were lower in all tree species in the most recent sampling. N, Ca, and Mg concentrations also declined in some species. These declines often resulted in decreased nutrient release rates during decomposition. Microarthropod populations differed significantly among litter species, as well as between years (probably resulting from differences in growing-season rainfall). For some litter species we found significant relationships between microarthropod populations and nutrient concentration (primarily C and N); however, most r 2values were low. Data suggest that changes in forest floor mass probably resulted from decreased litter quality and that those changes may have an effect on microarthropod populations. #
Alms and scope. Forest Ecology and Management publishes scientific articles concerned with forest... more Alms and scope. Forest Ecology and Management publishes scientific articles concerned with forest management and conservation, and in particular the application of biological, ecological and social knowledge to the management of man-made and natural forests. The scope of the journal includes all forest ecosystems of the world. A refereeing process ensures the quality and international interest of the manuscripts accepted for publication. The journal aims to encourage communication between scientists in disparate fields who share a common interest in ecology and natural-resource management, and to bridge the gap between research workers and forest managers in the field to the benefit of both. The journal should be of interest to research workers, managers and policy makers in forestry, natural resources, ecological conservation and related fields.
Journal of Environmental Quality, 2008
We predicted the eff ects of sulfate (SO 4 ) deposition on wilderness areas designated as Class I... more We predicted the eff ects of sulfate (SO 4 ) deposition on wilderness areas designated as Class I air quality areas in western North Carolina using a nutrient cycling model (NuCM). We used three S deposition simulations: current, 50% decrease, and 100% increase. We measured vegetation, forest fl oor, and root biomass and collected soil, soil solution, and stream water samples for chemical analyses. We used the closest climate stations and atmospheric deposition stations to parameterize NuCM. Th e areas were: Joyce Kilmer (JK), Shining Rock (SR), and Linville Gorge (LG). Th ey diff er in soil acidity and nutrients, and soil solution and stream chemistry. Shining Rock and LG have lower soil solution base cation and higher acidic ion concentrations than JK. For SR and LG, the soil solution Ca/Al molar ratios are currently 0.3 in the rooting zone (A horizon), indicating Al toxicity. At SR, the simulated Ca/Al ratio increased to slightly above 1.5 after the 30-yr simulation regardless of S deposition reduction. At LG, Ca/Al ratios ranged from 1.6 to 2.4 toward the end of the simulation period, the 100% increase scenario had the lower value. Low Ca/Al ratios suggest that forests at SR and LG are signifi cantly stressed under current conditions. Our results also suggest that SO 4 retention is low, perhaps contributing to their high degree of acidifi cation. Th eir soils are acidic, low in weatherable minerals, and even with large reductions in SO 4 and associated acid deposition, it may take decades before these systems recover from depletion of exchangeable Ca, Mg, and K.
Southern Appalachian forests are undergoing considerable change due to altered disturbance regime... more Southern Appalachian forests are undergoing considerable change due to altered disturbance regimes. For example, fire exclusion has had a major impact on the structure and function of pine-hardwood ecosystems. Recently, fire has been prescribed for a variety of applications: 1) stand-replacement in the form of a mimicked wildfire, 2) site-preparation as part of a fell-and-burn prescription, and 3) understory burning
The mixed oak-pine ecosystems in the southern Appalachians are in decline because of a combinatio... more The mixed oak-pine ecosystems in the southern Appalachians are in decline because of a combination of drought and southern pine-beetle infestation. A commonly applied prescription for restoration of these degraded sites has been to fell all vegetation, allow it to dry, and conduct a site-preparation burn. However, there is little information on the mid- and long-term influences of this prescription
Lab Rd, Otto, NC 28763). Effects of prescribed fire in mixed oak forests of the southern Appalach... more Lab Rd, Otto, NC 28763). Effects of prescribed fire in mixed oak forests of the southern Appalachians: forest floor, soil, and soil solution nitrogen responses. J. Torrey Bot. Soc. 136: 000-000. 2009-We examined nutrient cycling responses to prescribed fire on three sub-mesic, mixed-oak sites located in the Blue Ridge Physiographic province of the southern Appalachian Mountains: Alarka Laurel Branch (AL), Robin Branch (RB), and Roach Mill Branch (RM). Each study site was located within a sub-watershed that drained a first order stream. Our objective was to quantify the effects of prescribed burning on forest floor mass, nitrogen and carbon pools; and soil and soil water available nitrogen. Each site included a burned and unburned control area; both burned and control areas were sampled before and after burning. Within each plot, we sampled forest floor mass, carbon and nitrogen, soil and soil solution nitrate (NO3-N) and ammonium (NH4-N) concentrations before and after the prescribed burns. All prescribed fires were conducted in the dormant season and were low to moderate intensity. All sites lost a significant amount of forest floor mass due to burning; 82 to 91% of the Oi layer and 26 to 46% of the Oe + Oa layer. Soil NH4-N concentrations increased in surface soils (0-5 cm) only, immediately after burning, but return to pre-burn levels by mid-summer. Burning had no measurable effect on soil solution inorganic nitrogen concentrations. Low levels of solution NO3-N and NH4-N after burning and no change in stream NOi-N concentrations indicated that no inorganic nitrogen was lost from these sites.
Information is lacking on ecosystem effects of understory burning in mesic mixed-oak (Quercus spp... more Information is lacking on ecosystem effects of understory burning in mesic mixed-oak (Quercus spp.) forests of the southern Appalachians. Native Americans used periodic fires in these forests for driving game and opening the forest. In April 1998, we conducted a low- to moderate-intensity fire in a cove-hardwood forest in the Nantahala National Forest, western North Carolina. In March 1998, before
Environmental Pollution, 2002
The effects of harvest intensity (sawlog, SAW; whole tree, WTH; and complete tree, CTH) on biomas... more The effects of harvest intensity (sawlog, SAW; whole tree, WTH; and complete tree, CTH) on biomass and soil C were studied in four forested sites in the southeastern US (mixed deciduous forests at Oak Ridge, TN and Coweeta, NC; Pinus taeda at Clemson, SC; and P. eliottii at Bradford, FL). In general, harvesting had no lasting effects on soil C.
International Journal of Environmental Studies, 2008
GENV_A_286400.sg m We studied nitrogen (N) cycling pools and processes across vegetation and elev... more GENV_A_286400.sg m We studied nitrogen (N) cycling pools and processes across vegetation and elevation gradients in the southern Appalachian Mountains in SE USA. Measurements included bulk deposition input, water- shed export, throughfall fluxes, litterfall, soil N pools and processes, and soil solution N. N deposition increased with elevation and ranged from 9.5 to 12.4 kg ha −1 yr−1. In all
Soil Science Society of America Journal, 1994
Assessing potential long-term forest productivity requires identification of the processes regula... more Assessing potential long-term forest productivity requires identification of the processes regulating chemical changes in forest soils. We resampled the litter layer and upper two mineral soil horizons, A and AB/BA, in two aggrading southern Appalachian watersheds 20 yr after an earlier sampling. Soils from a mixed-hardwood watershed exhibited a small but significant decrease in soil pH. Extractable base cation content declined substantially in both mineral horizons. For example, Ca 2+ levels in the A horizon fell from 236 kg ha" 1 in 1970 to 80 kg ha" 1 in 1990. Proportionally, the decline was greatest for Mg 2 " 1 ", which dropped from 111 to 20 kg ha" 1 . A white pine (Pinus strobus L.) plantation was planted in 1956, after clear-felling hardwoods and recutting sprouts for 15 yr. Soil pH and base cation concentrations declined in the A horizon from 1970 to 1990. Soil pH declined from 5.9 to 5.0 and Ca 2+ levels from 534 to 288 kg ha" 1 . Cation content did not change significantly in the AB/BA soil horizon. Nutrient budgets were constructed using these soil and litter data plus existing data on weathering rates, forest productivity, and hydrologic fluxes and associated chemistry. Decreases in soil base cations and soil pH are attributed to leaching and to the sequestration of nutrients in biomass.
Soil Science Society of America Journal, 1995
The existence of several different methods for measuring net N mineralization and nitrification r... more The existence of several different methods for measuring net N mineralization and nitrification rates and indexing N availability has raised questions about the comparability of these methods. We compared in situ covered cores, in situ buried bags, aerobic laboratory incubations, and tension lysimetry on control and treated plots of a prescribed burn experiment in the southern Appalachians. Environmental influences were examined with soil moisture and temperature measurements. All methods detected significant differences in net N mineralization rates between treated and control plots; P = 0.04, 0.007,0.001, and 0.07 for covered cores, buried bags, lab incubations, and lysimeters, respectively. Mean rates of N mineralization during the growing season were similar for the three soil incubation methods. The laboratory incubation of soil from treated plots produced significantly greater potential nitrification rates than the in situ methods. The four methods were not well correlated; this indicates the need for caution when comparing N transformation data derived from different methods. We conclude that the in situ covered core method is superior because it best incorporates site-specific soil temperature and moisture changes into N transformation measurements.
Soil Science Society of America Journal, 1995
Soil Science Society of America Journal, 1997
Changes in surface soil C and N can resuh from forest management practices and may provide an ind... more Changes in surface soil C and N can resuh from forest management practices and may provide an index of impacts on long-term site productivity. Soil C and N were measured over time for five watersheds in the southern Appalachians: two aggrading hardwood forests, one south-and one north-facing, undisturbed since the 1920s; a white pine (Pinus strobus L.) plantation planted in 1956; and two regenerating hardwood forests, a whole-tree harvest in 1980, and a commercial sawlog harvest in 1977. Soils on harvested watersheds were sampled before and for =15 yr after harvest. Surface soil C concentration on the undisturbed watersheds varied significantly among sample years. Concentrations fluctuated on the south-facing and decreased on the north-facing watershed. The pattern for total N was similar. Total N decreased significantly on the north-facing but was stable on the southfacing watershed. In the white pine plantation, C increased while N concentrations decreased during the 20-yr period. Soil C and N concentrations generally declined the first year following whole-tree harvest. Fourteen years after cutting, C remained stable, while N was greater compared with reference watershed soils. The commercial sawlog harvest resulted in large increases in surface soil C and N concentrations immediately after cutting. Carbon levels remained elevated 17 yr following cutting. Our data suggest that the forest management practices examined do not result in long-term decreases in soil C and N. However, the high interannual variation on all watersheds suggests that care must be taken in selecting control sites to determine long-term treatment impacts.
Journal of Environment Quality, 2009
Establishment of riparian buff ers is an eff ective method for reducing nutrient input to streams... more Establishment of riparian buff ers is an eff ective method for reducing nutrient input to streams. However, the underlying biogeochemical processes are not fully understood. Th e objective of this 4-yr study was to examine the eff ects of riparian zone restoration on soil N cycling mechanisms in a mountain pasture previously degraded by cattle. Soil inorganic N pools, fl uxes, and transformation mechanisms were compared across the following experimental treatments: (i) a restored area with vegetation regrowth; (ii) a degraded riparian area with simulated eff ects of continued grazing by compaction, vegetation removal, and nutrient addition (+N); and (iii) a degraded riparian area with simulated compaction and vegetation removal only (-N). Soil solution NO 3 concentrations and fl uxes of inorganic N in overland fl ow were >90% lower in the restored treatment relative to the degraded (+N) treatment. Soil solution NO 3 concentrations decreased more rapidly in the restored treatment relative to the degraded (-N) following cattle (Bos taurus) exclusion. Mineralization and nitrifi cation rates in the restored treatment were similar to the degraded (-N) treatment and, on average, 75% lower than in the degraded (+N) treatment. Nitrogen trace gas fl uxes indicated that restoration increased the relative importance of denitrifi cation, relative to nitrifi cation, as a pathway by which N is diverted from the receiving stream to the atmosphere. Changes in soil nutrient cycling mechanisms following restoration of the degraded riparian zone were primarily driven by cessation of N inputs. Th e recovery rate, however, was infl uenced by the rate of vegetation regrowth.
Frontiers in Ecology and the Environment, 2005
Forest Ecology and Management, 1997
There is increasing concern about the effects of nutrient removal associated with various forest ... more There is increasing concern about the effects of nutrient removal associated with various forest harvesting practices on long-term site productivity. We measured exchangeable soil cation concentration responses to a commercial clearcut sawlog harvest in mixed hardwoods on a 59-ha watershed in the southern Appalachians. Soils were sampled 17 months prior to, and periodically for 17 years after, harvest. Concentrations of Ca, Mg, and K, increased significantly in the 0-10-cm soil layer for 3 years following harvest compared to pre-treatment levels. Concentrations of Mg and K were still significantly above pre-treatment levels 17-20 years following harvest. Calcium concentrations did not change significantly at the 10-30 cm depth, but both Mg and K showed significantly higher concentrations in some post-treatment years. Soils in the adjacent reference watershed showed no significant changes in soil cation concentrations over the same 17-year period. Results indicate that sawlog harvest using cable-yarding techniques on these sites does not adversely impact soil cation concentrations. © 1997 Elsevier Science B.V.
Forest Ecology and Management, 1999
Fine-hardwood ecosystems in the southern Appalachians are in serious decline due to fire exclusio... more Fine-hardwood ecosystems in the southern Appalachians are in serious decline due to fire exclusion and insect infestations. Fire has been advanced as a tool to restore these ecosystems, yet there are few studies evaluating overall ecosystem effects. Our objectives were to evaluate the effects of stand restoration burning on forest floor nitrogen (N) and carbon (C) pools, and soil and stream chemisuy. We measured changes in forest floor (coarse woody debris, small wood, litter, and humus) mass, N, and C; changes in soil chemistry (calcium (Ca), potassium (K), magnesium (Mg), cation exchange capacity (CEC), pH, C, and N); and changes in stream nitrate (NO& Results showed that significant reductions in mass, N, and C occurred only for litter and small wood on the ridge, where N losses were 52.9 kg ha-' for litter and small wood combined. No significant effects were observed on the mid-or lower slope of the treatment watershed. Losses on the ridge are considerably lower than losses which occur with alternative burning treatments used in the region, such as the fell and bum treatment. Soil and stream chemistry showed no response to burning. Spatial heterogeneity @ fire intensity (combustion temperatures ranged from d2->8OO"C) and severity associated with stand replacement burning results in a mosaic of fire effects and considerably less consumption and subsequent nutrient losses. 0 1999 Elsevier Science B.V. All rights reserved.
Forest Ecology and Management, 2004
Understory prescribed burning is being suggested as a viable management tool for restoring degrad... more Understory prescribed burning is being suggested as a viable management tool for restoring degraded oak-pine forest communities in the southern Appalachians yet information is lacking on how this will affect ecosystem processes. Our objectives in this study were to evaluate the watershed scale effects of understory burning on total aboveground biomass, and the carbon and nitrogen pools in coarse woody debris (CWD), forest floor and soils. We also evaluated the effects of burning on three key biogeochemical fluxes; litterfall, soil CO 2 flux and soil net nitrogen mineralization. We found burning significantly reduced understory biomass as well as the carbon and nitrogen pools in CWD, small wood and litter. There was no significant loss of carbon and nitrogen from the fermentation, humus and soil layer probably as the result of low fire intensity. Burning resulted in a total net loss of 55 kg ha À1 nitrogen from the wood and litter layers, which should be easily replaced by future atmospheric deposition. We found a small reduction in soil CO 2 flux immediately following the burn but litterfall and net nitrogen mineralization were not significantly different from controls throughout the growing season following the burn. Overall, the effects of burning on the ecosystem processes we measured were small, suggesting that prescribed burning may be an effective management tool for restoring oak-pine ecosystems in the southern Appalachians. Published by Elsevier B.V.
Forest Ecology and Management, 2005
Soil nutrient concentrations decreased in an aggrading southern Appalachian forest over a 20-year... more Soil nutrient concentrations decreased in an aggrading southern Appalachian forest over a 20-year period. Construction of nutrient budgets showed significant nutrient sequestration aboveground including increased forest floor mass. We hypothesized that the changes in forest floor mass resulted from decreased litter decomposition rates because of decreased litter quality. In 1992 and 1993, we repeated a litter decomposition experiment conducted in 1969 and 1970 to test this hypothesis. In addition, we examined microarthropod populations and functional groups as litter decomposed. For four of the five species tested, firstyear decomposition rates were about the same in both experiments. Initial litter nutrient concentrations of P were lower in all tree species in the most recent sampling. N, Ca, and Mg concentrations also declined in some species. These declines often resulted in decreased nutrient release rates during decomposition. Microarthropod populations differed significantly among litter species, as well as between years (probably resulting from differences in growing-season rainfall). For some litter species we found significant relationships between microarthropod populations and nutrient concentration (primarily C and N); however, most r 2values were low. Data suggest that changes in forest floor mass probably resulted from decreased litter quality and that those changes may have an effect on microarthropod populations. #