Relative contributions of soil, foliar, and woody tissue respiration to total ecosystem respiration in four pine forests of different ages

Carbon dioxide (CO2) emissions from soil, foliage, and live woody tissue were measured throughout the year in afforested, white pine (Pinus strobus L.) stands (67, 32, 17, and 4 years old as of 2006), growing in a northern temperate climate. The data were used to estimate annual ecosystem respiration (Re) and its component fluxes, including soil, foliar, and woody tissue respiration; to investigate major environmental factors causing intersite and temporal variability in the observed fluxes; and to compare chamber-based Re estimates with eddy covariance-based estimates. While temperature was the dominant driving factor of temporal variability in component fluxes, intersite variability in CO2 emissions was attributed to differences in stand physiological characteristics, such as the presence of the LFH soil horizon, its carbon-to-nitrogen ratio, and the amount of canopy cover. Additional factors that contributed to flux variability included the frequency of precipitation events, vapor pressure deficit and stem diameter, depending on the component considered. Estimated annual chamber-based totals of Re across the four stands were 1526 +/- 137, 1278 +/- 137, 1985 +/- 293, and 773 +/- 46 g C m(-2) yr(-1) for the 67-, 32-, 17-, and 4-year-old stands, respectively. Soil respiration dominated emissions at the 4-year-old stand, while foliar respiration dominated emissions at the 17-year-old stand. In contrast, at the two oldest stands, soil and foliar respirations were comparable. Soil respiration accounted for 44%, 44%, 26%, and 70% of annual Re, across the 67-, 32-, 17-, and 4-year-old stands, while foliar respiration accounted for 48%, 41%, 60%, and 30% of annual Re, across the respective sites. Wood respiration was the smallest component of annual Re across the stands (8%, 15%, 14%, and 0.1%, respectively). The chamber-based Re values were higher than tower-based eddy covariance Re estimates, on average by 18%, 70%, 18%, and 36% at the 67-, 32-, 17-, and 4-year-old stands, respectively. This study contributes to our general understanding of the age-related effects and the role of climate on carbon emissions from various components of afforested ecosystems. Our results suggest that foliar respiration could be comparable to or higher than soil respiration in its contribution to Re in young to mature, planted or afforested, ecosystems. They also suggest that site quality and stand age are important factors to be considered in future studies of carbon dynamics of afforested stands