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Assessing the potential impacts to riparian ecosystems resulting from hemlock mortality in Great Smoky Mountains National Park.

Roberts SW, Tankersley R, Orvis KH - Environ Manage (2009)

Bottom Line: The loss of hemlock from riparian forests in Great Smoky Mountains National Park (GSMNP) may result in significant physical, chemical, and biological alterations to stream environments.The results of this study suggest that the replacement of hemlock overstory with hardwood species will have minimal impact on long-term stream conditions, however disturbance during the transition is likely to have significant impacts.Management of riparian forests undergoing hemlock decline should, therefore, focus on facilitating a faster transition to hardwood-dominated stands to minimize long-term effects on water quality.

View Article: PubMed Central - PubMed

Affiliation: Department of Geography, University of Tennessee, Knoxville, TN, USA. sroberts@lifesci.ucsb.edu

ABSTRACT
Hemlock Woolly Adelgid (Adelges tsugae) is spreading across forests in eastern North America, causing mortality of eastern hemlock (Tsuga canadensis [L.] Carr.) and Carolina hemlock (Tsuga caroliniana Engelm.). The loss of hemlock from riparian forests in Great Smoky Mountains National Park (GSMNP) may result in significant physical, chemical, and biological alterations to stream environments. To assess the influence of riparian hemlock stands on stream conditions and estimate possible impacts from hemlock loss in GSMNP, we paired hardwood- and hemlock-dominated streams to examine differences in water temperature, nitrate concentrations, pH, discharge, and available photosynthetic light. We used a Geographic Information System (GIS) to identify stream pairs that were similar in topography, geology, land use, and disturbance history in order to isolate forest type as a variable. Differences between hemlock- and hardwood-dominated streams could not be explained by dominant forest type alone as forest type yields no consistent signal on measured conditions of headwater streams in GSMNP. The variability in the results indicate that other landscape variables, such as the influence of understory Rhododendron species, may exert more control on stream conditions than canopy composition. The results of this study suggest that the replacement of hemlock overstory with hardwood species will have minimal impact on long-term stream conditions, however disturbance during the transition is likely to have significant impacts. Management of riparian forests undergoing hemlock decline should, therefore, focus on facilitating a faster transition to hardwood-dominated stands to minimize long-term effects on water quality.

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Discharge, pH, and Nitrate concentrations among six pairs of hemlock and hardwood-dominated streams
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Fig1: Discharge, pH, and Nitrate concentrations among six pairs of hemlock and hardwood-dominated streams

Mentions: Neither hemlock- nor hardwood-dominated streams had consistently higher nitrate concentrations among all pairs (Fig. 1). For each pair, we found equal variance and no significant difference in mean nitrate concentrations between hemlock- and hardwood-dominated streams. Nitrate concentrations in all streams ranged from 0.0023 to 0.1356 mg/L N03-N with an average of 0.0399 mg/L N03-N. Although differences were not significant, hardwood-dominated streams had higher nitrate concentrations in pairs 1 and 2 (P = 0.762, and 0.984, respectively), while hemlock-dominated streams had higher nitrate concentrations in pairs 3, 4, 5, and 6 (P = 0.248, 0.253, 0.155, and 0.07, respectively).Fig. 1


Assessing the potential impacts to riparian ecosystems resulting from hemlock mortality in Great Smoky Mountains National Park.

Roberts SW, Tankersley R, Orvis KH - Environ Manage (2009)

Discharge, pH, and Nitrate concentrations among six pairs of hemlock and hardwood-dominated streams
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2717373&req=5

Fig1: Discharge, pH, and Nitrate concentrations among six pairs of hemlock and hardwood-dominated streams
Mentions: Neither hemlock- nor hardwood-dominated streams had consistently higher nitrate concentrations among all pairs (Fig. 1). For each pair, we found equal variance and no significant difference in mean nitrate concentrations between hemlock- and hardwood-dominated streams. Nitrate concentrations in all streams ranged from 0.0023 to 0.1356 mg/L N03-N with an average of 0.0399 mg/L N03-N. Although differences were not significant, hardwood-dominated streams had higher nitrate concentrations in pairs 1 and 2 (P = 0.762, and 0.984, respectively), while hemlock-dominated streams had higher nitrate concentrations in pairs 3, 4, 5, and 6 (P = 0.248, 0.253, 0.155, and 0.07, respectively).Fig. 1

Bottom Line: The loss of hemlock from riparian forests in Great Smoky Mountains National Park (GSMNP) may result in significant physical, chemical, and biological alterations to stream environments.The results of this study suggest that the replacement of hemlock overstory with hardwood species will have minimal impact on long-term stream conditions, however disturbance during the transition is likely to have significant impacts.Management of riparian forests undergoing hemlock decline should, therefore, focus on facilitating a faster transition to hardwood-dominated stands to minimize long-term effects on water quality.

View Article: PubMed Central - PubMed

Affiliation: Department of Geography, University of Tennessee, Knoxville, TN, USA. sroberts@lifesci.ucsb.edu

ABSTRACT
Hemlock Woolly Adelgid (Adelges tsugae) is spreading across forests in eastern North America, causing mortality of eastern hemlock (Tsuga canadensis [L.] Carr.) and Carolina hemlock (Tsuga caroliniana Engelm.). The loss of hemlock from riparian forests in Great Smoky Mountains National Park (GSMNP) may result in significant physical, chemical, and biological alterations to stream environments. To assess the influence of riparian hemlock stands on stream conditions and estimate possible impacts from hemlock loss in GSMNP, we paired hardwood- and hemlock-dominated streams to examine differences in water temperature, nitrate concentrations, pH, discharge, and available photosynthetic light. We used a Geographic Information System (GIS) to identify stream pairs that were similar in topography, geology, land use, and disturbance history in order to isolate forest type as a variable. Differences between hemlock- and hardwood-dominated streams could not be explained by dominant forest type alone as forest type yields no consistent signal on measured conditions of headwater streams in GSMNP. The variability in the results indicate that other landscape variables, such as the influence of understory Rhododendron species, may exert more control on stream conditions than canopy composition. The results of this study suggest that the replacement of hemlock overstory with hardwood species will have minimal impact on long-term stream conditions, however disturbance during the transition is likely to have significant impacts. Management of riparian forests undergoing hemlock decline should, therefore, focus on facilitating a faster transition to hardwood-dominated stands to minimize long-term effects on water quality.

Show MeSH
Related in: MedlinePlus