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1 January 2010 Soil Properties in Old-Growth Douglas-Fir Forest Gaps in the Western Cascade Mountains of Oregon
Robert P. Griffiths, Andrew N. Gray, Thomas A. Spies
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This was a study of vegetation and soil properties in tree-fall gaps in a coniferous forest of the Pacific Northwest. It had three objectives: (1) to determine if there are correlations between above-ground vegetation and below-ground soil properties within large 50 m diameter gaps, (2) to determine how large gaps influence forest soils compared with non-gap soils, and (3) to measure the effects of differently sized gaps on gap soils. To address these objectives, circular canopy gaps were created in old-growth Douglas-fir forests of the H. J. Andrews Experimental Forest in the western Oregon Cascade Mountains. To address the first objective, within-gap soil spatial patterns were compared with above ground distributions of both vegetation and large woody debris in two large gaps. Spatial and Pearson correlation analyses showed no consistent correlations between soil characteristics and above ground vegetation and coarse woody debris. With reference to the second objective, statistically significant differences between gap and non-gap soil characteristics were observed. Soil moisture, temperature and denitrification potentials were all elevated in forest 50 m diameter gaps and litter depth, labile C, soil respiration, β-gluosidase activity, and ectomytcorrhizal mat concentrations were all reduced. Comparisons between north and south gap soils, showed significant differences in soil characteristics in one but not the other 50 m gap. The third objective was addressed by documenting gap size effects on differences between gap and non gap soil characteristics in two gaps each of 10, 20, 30, and 50 m diameter. Differences between gap and nongap soil moisture, litter depth and ectomycorrhizal mat coverages were essentially the same regardless of gap size. Soil respiration rates and soil organic matter concentrations were similar in 10 m gaps but both lower in gaps 20 m and larger.

© 2010 by the Northwest Scientific Association.
Robert P. Griffiths, Andrew N. Gray, and Thomas A. Spies "Soil Properties in Old-Growth Douglas-Fir Forest Gaps in the Western Cascade Mountains of Oregon," Northwest Science 84(1), 33-45, (1 January 2010).
Received: 9 February 2009; Accepted: 1 July 2009; Published: 1 January 2010

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