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Description

It is increasingly essential to develop a comprehensive understanding of forest processes so that we may better conserve and maintain our old-growth forests in the face of climate change. In the Pacific Northwest, logs might elevate and remove conifer seedlings from light competition with moss and herbs, but seedlings growing on the forest floor may benefit from log shade. Moss can retain moisture which may result in higher water availability for seedlings, but in droughty conditions the desiccated moss might leave seedlings ‘high and dry’. Logs increase mircrosite heterogeneity, providing cool, moist microclimates for seedlings and protecting them from droughty summer conditions and direct solar radiation. The purpose of my study was to determine whether logs and moss facilitate conifer seedling establishment on the forest floor, to examine which factors may influence seedling establishment on logs instead of the forest floor, and to determine whether these relationships differ with different moisture availability.The Wind River Forest Dynamics Plot (WFDP) is a 500 year old forest in the south Washington Cascades, containing 133 seedling quadrats in a regular grid and 9,987 mapped pieces of coarse woody debris. The forest floor had taller moss but lower moss cover, whereas log surfaces had shorter moss and higher moss cover. Logs and the forest floor had the same herb height, and both had more moss in wet areas than dry areas of the WFDP. Conifer seedlings were taller and more abundant on top on logs and, on the forest floor, the data of seedling density and log proximity was consistent with the hypothesis that logs facilitate seedling establishment. Moss cover limited seedling establishment in both wet and dry areas, but data indicated seedlings had different relationships to moss height in wet and dry areas. My findings suggest that moss is a better indicator of seedling abundance than log proximity, but these relationships may change when seedlings have different limiting pressures such as moisture in dry areas or light in wet areas of the WFDP.

Publication Date

12-9-2021

City

Logan, UT

Keywords

old-growth forests, climate change, Pacific Northwest, moss

Disciplines

Forest Sciences

Log Proximity and Moss as Indicators of Conifer Seedling Abundance in Old-Growth Douglas-Fir/ Hemlock Forests

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