Influence of Thinning on Soil CO 2 Efflux in Chinemse Fir Plantations

Abstract

ABSTRACT Forest management is expected to influence soil CO 2 efflux ( F CO 2 ) as a result of changes in microenvironmental conditions, soil microclimate, and root dynamics. Soil F CO 2 rate was measured during the growing season of 2006 in both thinning and non-thinning locations within stands ranging from 0 to 8 years after the most recent thinning in Chinese fir ( Cunninghamia lanceolata (Lamb.) Hook) plantations in Huitong Ecosystem Research Station, Hunan, China. Soil temperature and moisture were also measured to examine relationships between F CO 2 and soil properties. Forest thinning resulted in huge changes in F CO 2 that varied with time since cutting. Immediately following harvest (year 0) F CO 2 in thinning area increased by about 30%, declined to 20%–27% below pre-cutting levels during years 4–6, and recovered to pre-cutting levels at 8 years post-cutting. A similar temporal pattern, but with smaller changes, was found in non-thinning locations. The initial increase in F CO 2 could be attributed to a combination of root decay, soil disturbance, and increased soil temperature in gaps, while the subsequent decrease and recovery to the death and gradual regrowth of active roots. Strong effects of soil temperature and soil water content on F CO 2 were found. Forest thinning mainly influenced F CO 2 through changes in tree root respiration, and the net result was a decrease in integrated F CO 2 flux through the entire felling cycle.