2009 Harvard Forest REU Student Symposium Abstracts
Maggie Wagner - Duke University
Mortality, coarse woody debris, and nutrient cycling over 20 years in a virgin Tsuga canadensis forest in New Hampshire
Coarse woody debris (CWD) studies are common in Europe and western North America, but are somewhat neglected in the eastern United States. CWD has been shown to provide important plant and animal habitat and contribute to both terrestrial and aquatic nutrient cycles. We surveyed 57 ten-by-ten meter plots in the Harvard tract of the Pisgah State Park in southwestern New Hampshire, one of the few parcels of primary forest remaining in New England. The surveys were conducted in 1989 and 2009. In each plot, we measured and mapped every tree (all stems ≥ 2.5 cm diameter at breast height) and every piece of CWD (all stumps, snags, and downed wood with an average diameter ≥ 10 cm). In 2009 we also analyzed the C and N contents of soil samples from beneath and adjacent to a variety of coarse woody debris. Censuses showed that all major tree species declined between surveys, with eastern hemlock (Tsuga canadensis) suffering mortality at half the rate of the hardwoods (Acer rubrum, Fagus grandifolia, and Betula spp.). Mortality rates did not appear to differ among substrates (soil vs. rock vs. tip-ups). Total CWD decreased from 354.6 m3/ha to 215.5 m3/ha. CWD input over 20 years was 8.4 m3/ha and was outpaced by volume loss due to the decay of debris added by the major hurricane of 1938. The basal area of snags increased slightly from 2.64 m2/ha to 2.78 m2/ha. Under CWD, soil C:N was higher (p = 0.0042) and soil N was lower (p = 0.0238) than they were 1 m away from debris. These results suggest that CWD is an important structural component of primary New England forests, and its effects on nutrient cycling should be investigated further.
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