Seasonal patterns in soil surface CO2 flux under snow cover in 50 and 300 year old subalpine forests

Abstract

Soil CO2 flux can contribute as much as 60-80% of total ecosystem respiration in forests. Although considerable research has focused on quantifying this flux during the growing season, comparatively little effort has focused on non-growing season fluxes. We measured soil CO2 efflux through snow in 50 and � 300 year old subalpine forest stands near Fraser CO. Our objectives were to quantify seasonal patterns in wintertime soil CO2 flux; determine if differences in soil CO2 flux between the two forest ages during the growing season persist during winter; and to quantify the sample size necessary to discern treatment differences. Soil CO2 flux during the 2002-2003 and 2003-2004 snow season averaged 0.31 and 0.35 lmols m � 2 s � 1 for the young and old forests respectively; similar to the relative difference observed during summer. There was a significant seasonal pattern of soil CO2 flux during the winter with fluxes averaging 0.22 lmols m � 2 s � 1 in December and January and increasing to an average of 0.61 lmols m � 2 s � 1 in May. Within-plot variability for measurements used in calculating flux was low. The coefficients of variation (CV) for CO2 concentration, snowpack density, and snow depth were 17, 8 and 14%, respectively, yielding a CV for flux measurements within-plot of 29%. A within plot CV of 29% requires 8 sub-samples per plot to estimate the mean flux with a standard error of ±10% of the mean. Variability in CO2 flux estimates among plots (size = 400 m 2 ) was similar to that within plot and was also low (CV = � 28%). With a CV of 28% among plots, ten plots per treatment would have a 50% probability of detecting a 25% difference in treatment means for a = 0.05.