Soil properties in old-growth Douglas-fir gaps in the western Cascade Mountains of Oregon

Abstract

This study had three objectives: (1) to determine if there are correlations between aboveground vegetation and belowground soil properties within large 50-m-diameter gaps, (2) to determine how large gaps influence forest soils compared with nongap soils, and (3) to measure the effects of differently sized gaps on gap soils. Circular canopy gaps were created in old-growth Douglas-fir forests of the H.J. Andrews Experimental Forest in the western Oregon Cascade Mountains. Within-gap soil spatial patterns were compared with aboveground 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. Statistically significant differences between gap and nongap soil characteristics were observed. Soil moisture, temperature, and denitrification potentials were all elevated in forest 50-m-diameter gaps, and litter depth, labile carbon, soil respiration, B-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. Two gaps each of 10, 20, 30, and 50 m diameter showed no differences between gap and nongap soil moisture litter depth and ectomycorrhizal mat coverages, 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.

Citation

Griffiths, R.P.; Gray, A.N.; Spies, T.A. 2010. Soil properties in old-growth Douglas-fir gaps in the western Cascade Mountains of Oregon. Northwest Science. 84(1): 33-45.