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- Title
Impacts of Hemlock Loss on Nitrogen Retention Vary with Soil Nitrogen Availability in the Southern Appalachian Mountains.
- Authors
Block, Corinne; Knoepp, Jennifer; Elliott, Katherine; Fraterrigo, Jennifer
- Abstract
The impacts of exotic insects and pathogens on forest ecosystems are increasingly recognized, yet the factors influencing the magnitude of effects remain poorly understood. Eastern hemlock ( Tsuga canadensis) exerts strong control on nitrogen (N) dynamics, and its loss due to infestation by the hemlock woolly adelgid ( Adelges tsugae) is expected to decrease N retention in impacted stands. We evaluated the potential for site variation in N availability to influence the magnitude of effects of hemlock decline on N dynamics in mixed hardwood stands. We measured N pools and fluxes at three elevations (low, mid, high) subjected to increasing atmospheric N deposition where hemlock was declining or absent (as reference), in western North Carolina. Nitrogen pools and fluxes varied substantially with elevation and increasing N availability. Total forest floor and mineral soil N increased ( P < 0.0001, P = 0.0017, resp.) and forest floor and soil carbon (C) to N ratio decreased with elevation ( P < 0.0001, P = 0.0123, resp.), suggesting that these high elevation pools are accumulating available N. Contrary to expectations, subsurface leaching of inorganic N was minimal overall (<1 kg ha 9 months), and was not higher in stands with hemlock mortality. Mean subsurface flux was 0.16 ± 0.04 (SE) (kg N ha 100 days) in reference and 0.17 ± 0.05 (kg N ha 100 days) in declining hemlock stands. Moreover, although subsurface N flux increased with N availability in reference stands, there was no relationship between N availability and flux in stands experiencing hemlock decline. Higher foliar N and observed increases in the growth of hardwood species in high elevation stands suggest that hemlock decline has stimulated N uptake and growth by healthy vegetation within this mixed forest, and may contribute to decoupling the relationship between N deposition and ecosystem N flux.
- Subjects
APPALACHIAN Basin; EASTERN hemlock; INTRODUCED insects; NITROGEN in soils; CARBON in soils; ATMOSPHERIC nitrogen
- Publication
Ecosystems, 2012, Vol 15, Issue 7, p1108
- ISSN
1432-9840
- Publication type
Article
- DOI
10.1007/s10021-012-9572-9