Publication Date

2013

Document Type

Honors Thesis

Department

Biological Sciences

Keywords

Biogeochemistry, Biodegradation, Chemical weathering, Decomposition (Chemistry), Precipitation (Chemistry), Ecological disturbances, Biotic communities, Soil chemistry, Nitrogen, Forest litter, Eastern hemlock, Soil nitrogen, Leaf litter, Ecosystem change, Hemlock

Abstract

The loss of foundation species as a result of environmental change or exotic species invasions can alter community composition and ecosystem function. The spread of hemlock woolly adelgid (Adelges tsugae) in eastern North America that threatens the survival of eastern hemlock (Tsuga canadensis), a foundation species, and has also motivated pre-emptive logging efforts. In the northeastern United States, ecological succession following hemlock loss will eventually produce a deciduous hardwood forest, a change in forest type that might produce significant changes in ecosystem processes, such as nutrient cycling and decomposition. Comparisons between mature deciduous forests and mature hemlock forests have been used to predict future structure and function of forests affected by hemlock removal. Consequently, little is known about nutrient cycling in the several decade span of intermediate stages in forest succession, especially in early-successional forests dominated by black birch (Betula lenta) that replace mature hemlock forest in the northeastern United States. This study used a paired-plot design to compare throughfall chemistry, litterfall, litter decomposition, and soil chemistry in adjacent mature hemlock forest and young black birch forest patches from which hemlocks were logged in the late 1980s at the MacLeish Field Station in Whately, MA to investigate effects of hemlock removal after twenty years. Deposition of most ions in throughfall was greater in the hemlock forest than black birch forests (p < 0.05), implying that canopy structure and tree physiology have a strong influence on throughfall, more so that foliar chemistry alone. Decomposition rates of black birch and hemlock litter did not differ between forest types (p > 0.05), suggesting that changes in microclimate may not influence decomposition rates as much as changes in litter type would. Net nitrification rates and cation exchange capacity of the young black birch forest did not differ from the mature hemlock forests, whereas net nitrification rates and base saturation were higher in a mature deciduous reference plot. These results suggest that the early-successional forests that have replaced hemlock at this site do not yet resemble mature deciduous forests in terms of nutrient cycling characteristics, which suggests that it may take many decades before nutrient cycling in regrowth forests resembles that in deciduous forests.

Language

English

Comments

130 p. : col. ill., col. map. Honors project-Smith College, 2013. Includes bibliographical references (p. 107-112)

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