PARENT SESSION
Poster Session #19: Nutrient Cycling.
Tuesday, August 7, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall
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Ecosystem function changes following hemlock harvesting in New England .
Kizlinski, M1, Foster, D1, Orwig, D1, 1
ABSTRACT- Due to its low timber value, eastern hemlock (Tsuga canadensis) has been ignored by intensive silvicultural and ecosystem research typical of more valuable species. However, widespread logging of hemlock forests has dramatically increased in Connecticut and Massachusetts in response to ongoing infestations of an exotic forest pest, the hemlock woolly adelgid (Adelges tsugae). This study examines nitrogen cycling dynamics, decomposition rates, and key environmental factors at 10 sites ranging from 1 to 13 years after hemlock harvesting. Identical measurements were collected from unlogged portions of each hemlock stand. Nitrogen cycling was measured using two consecutive 10-week soil core incubations. Relative to intact stands (74.2 kg/ha), recent cuts exhibited lower total nitrogen mineralization rates (69.6 kg/ha), while older cuts showed higher rates (98.0 kg/ha). Nitrification rates were very low in intact stands (7.9 kg/ha) while harvested stands showed significant elevated nitrate production (21.8 kg/ha). Decomposition rates, measured by filter paper mass loss, were lowest in recent cuts (35.9% mass loss) and highest in older cuts (79.5%) relative to intact stands (59.1%) indicating a shift towards a different decomposition environment. Laboratory incubation experiments revealed differences in litter quality that led to increased decomposition rates of forest floor material from cut stands versus intact stands. This study suggests hemlock harvesting results in immediate and long-lasting changes in ecosystem function that may play a prominent role in future dynamics of these sites.
KEY WORDS: logging, hemlock, nitrogen cycling, ecosystem function