Coarse woody debris and soil respiration in a clearcut on the Olympic Peninsula, Washington, U.S.A.

Abstract

Coarse woody debris (CWD) and soil respiration rates were measured using soda lime traps on a clearcut site in the Hoh River Valley on the west side of the Olympic Peninsula, Washington. The influence of species of CWD (western hemlock (Tsugaheterophylla (Raf.) Sarg.) and Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco)), decay class, and log diameter on respiration rates was determined. CWD and soil respiration were measured every 4 weeks from October 1991 to November 1992 along with CWD and soil temperature and moisture contents. Western hemlock logs respired at a significantly higher rate (4.05 g CO 2 •m −2 •day −1 ) than Douglas-fir logs (2.94 g CO 2 •m −2 •day −1 ). There were no significant differences between respiration rates for decay classes 1–2, 3, and 5 logs (4.47, 3.69, and 4.28 g CO 2 •m −2 •day −1 , respectively), and there was no strong relationship between CWD respiration rate and log diameter. The highest average respiration rate was from the soil in the clearcut (5.22 g CO 2 •m −2 •day −1 ). Averaged for the year, log and soil respiration rates in the clearcut site were similar to those in an adjacent old-growth forested site. However, seasonal fluctuations were greater on the clearcut site. Higher summer respiration rates and lower winter rates observed on the clearcut relative to the old-growth site appeared to be driven more by temperature than by moisture. Clear-cutting also resulted in higher summer CWD and soil temperatures and lower winter temperatures compared with the old-growth site.