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Concannon, J.A., 1995

Characterizing structure, microclimate, and decomposition of peatland, beachfront, and newly-logged forest edges in southeastern Alaska

Bibliographic Reference

Concannon, J.A., 1995, Characterizing structure, microclimate, and decomposition of peatland, beachfront, and newly-logged forest edges in southeastern Alaska: University of Washington, Seattle, Ph.D. dissertation, 325 p., illust., maps.


In this study, I examined the forest structure, composition, microclimate, and decomposition of three common edge types in southeastern Alaska including; peatland, beachfront, and new clearcuts adjacent to productive western hemlock-Sitka spruce forests. Sites were located on 4 larger islands of the Alexander Archipelago in southeastern Alaska. The study was focussed on transects extending from the open area, through the forest boundary to 200 m into the forest. Twenty-two edges were examined during 1990 and 1991. Forest structure was unique for each edge type. Peatland-forest edges exhibit feathered transition of short and sparse tree growth to large dense old-growth western hemlock-Sitka spruce forests. Beachfront-forest edges were sealed at the boundary by a multi-layering of shrubs, small trees, mid-canopy trees, and some emergents. The transition to large productive old-growth was abrupt. Clearcut-forest edges were essentially old-growth forests opened up by logging. Average size of trees at the boundary was large but stand size and productivity decreased moving into the forest. Productive western hemlock-Sitka spruce associations were not apparent for a long distance into the forest. Herbaceous cover appeared to be directly linked to light levels along the forest transects. Because structure was so inherently different for each edge type, microclimatic gradients from open area to the forest interior environment varied with edge type. The strongest gradients were observed on sunny and extremely windy days. An edge index value (EIV) was calculated to differentiate edge-affected microclimate from interior environments. Edge type influenced forest microclimate such that; (1) Peatlands affected interior radiation and air temperature range for 120 m into the forest until interior environments were encountered. (2) Beachfront-forests were penetrated by ocean winds for up to 120 m however, other variables such as interior air temperature and relative humidity were only influenced for 30 m into the forest and (3) Clearcuts affected air temperature range between maxima and minima and relative humidity for up to 200 m into the forest. In turn, edge type affected decomposition in adjacent forests. The decomposition gradient of filter paper increased from the peatland into the forest but decreased into the forest along beachfront and clearcut-forest edges. Microclimatic gradients in edge-affected areas of the forest were more strongly related to mass loss of filter paper-along clearcut-forest edges than in forests adjacent to natural edges. Correlation analyses and linear regression separated out different experimental, logistical, and seasonal variables that influenced microclimate and decomposition. As with most edge studies, edge-affected portion of the forest differs with the variable of interest. In this study edge width varied from 30 m to over 200 m into the forest. This study quantified edge width of the selected variables. Edge width is required to calculate forest patch size that will include old-growth environment (given different patch size and shape). Amount of forest interior environment is required to calculate old-growth species viability given natural and clearcut-generated edge in a landscape. (Abstract shortened by UMI.)

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