Ecosystem respiration (ER) was measured with the eddy covariance technique in 14 forest ecosystems in the Upper Great Lakes Region during the growing seasons of 2002 and 2003. The response of ER to soil temperature and moisture was analyzed using empirical models. On average, ER was higher in the intermediate and young than in the mature stands, and higher in hardwood than in conifer stands. The seasonal mean temperature-normalized respiration rate (R10) ranged from 1 to 3 μmol CO2 m-2 s-1 and seasonal mean activation energy (Ea) from 40 to 110 kJ mol-1. The variation in the residuals of temperature response function of ER was best explained by soil moisture content. ER showed higher temperature sensitivity (as indicated by lower Ea) in the young than in the mature stands of coniferous forests, but not in the hardwood forests. The inclusion of soil moisture as an explicit driver of R10 explained an additional 8% (range 0-21%) of variability in ER. Significant moisture sensitivity of ER was detected in only 5 out of 20 site-years and it was associated with bimodal soil moisture distribution. Moisture sensitivity could partially be predicted from statistical moments kurtosis and interquartile range. The data implied greater moisture sensitivity with increasing stand age, possibly due to faster depletion of soil water supplies from a greater evaporative surface in the older stands. Additional limiting factors to ER were implicated.
|Original language||English (US)|
|Number of pages||15|
|Journal||Agricultural and Forest Meteorology|
|State||Published - Feb 13 2008|
Bibliographical noteFunding Information:
The study was supported by grants from National Science foundation (JC), Department of Energy (DOE) National Institute for Global Environmental Change (CSV, KJD, PVB), DOE Office of Biological and Environmental Research Terrestrial Carbon Processes (KJD, PVB), USDA FS North Central Research Station (JC) and USDA FS Southern Global Change Program (AN, JC). We also thank the Washburn Ranger District, WLEF public radio station and other site land owners for facilitating the research. We gratefully acknowledge the support of field crew members, technicians and engineers. Special thanks to Dr. J. DeForest for his insightful comments on an earlier version of this manuscript.
- Activation energy
- Boreo-temperate forests
- Ecosystem respiration
- Eddy covariance
- Forest age
- Moisture sensitivity
- Soil moisture
- Soil temperature
- Temperature sensitivity