Ecosystem Studies and Management
At the Howland forest, WHRC scientists measure soil respiration and examine the effects of climatic variables through long term plots and amendment experiments. Soil respiration measurements are performed with both the manual and automated systems.
Long term soil respiration measurements began in 1995 with four plots, each containing eight respiration collars. Two of the plots are better drained sites, upland, while the other two are wetland sites. Automated soil respiration measurements began in 2004 with six autochambers located around the main eddy covariance tower.
Methods and Measurements
Manual Soil Respiration Measurements
Manual measurements of soil respiration were initially made using the system described in the Harvard forest soil respiration section. In 2007, after careful comparison between systems, the system was changed as follows:
Manual measurements of soil respiration, using a vented, flow through, non-steady-state system were made once per week between 09.00 h and 15.00 h. Soil respiration was measured using a Vaisala GMP343 CO2 analyzer and a 21X Campbell Scientific data logger system that is housed in a metal suitcase. The calibration of the analyzer was checked before each measurement. The analyzer was connected to a vented white acrylonitrile butadiene styrene (ABS) chamber top (10 cm in height) that is placed over a collar already in the ground. A pump circulates the air at a rate of 0.5 l min±1 from the chamber top to the analyzer and back to the chamber top. The analyzer and the pump are both powered from the data logger. The collars, 25 cm in diameter (0.05 m2 surface area), are made from thin-walled PVC tubing were cut into 10 cm lengths and inserted into the ground to a depth of approximately 5 cm. The chamber top was left on the collar for 5 min, and the change in CO2 concentration within the chamber was recorded on the 21X data logger. A linear regression was performed on the increasing concentration to determine a flux rate, which was corrected for atmospheric pressure and chamber air temperature.
Automated Measurements of Soil Respiration: We have been taking automated measurements of soil respiration at the main tower location since 2004. For a description of the automated system, please review the Harvard forest automated system.
- Long term soil respiration measurements show increasing soil respiration rates with increasing temperature and moisture.
- Periods of prolonged drought decrease respiration rates in well drained sites but increase it in wetland.
- The ratio of soil respiration to total ecosystem respiration (Rs/Reco) reaches a minimum of about 0.45 in the early spring, gradually increases through the late spring and early summer, levels off at about 0.65 for the summer, and then increases again to about 0.8 in the autumn.
- Diel patterns of soil respiration indicate a link between tree activity and respiration rates. This is likely the root respiration component of soil respiration and its link to above ground tree activity.
Savage, K.E., and E.A. Davidson. 2001. Interannual variation of soil respiration in two New England forests. Global Biogeochemical Cycles 15:337-350. Richardson, A.D., B.H. Braswell, D.Y. Hollinger, P. Burman, E.A. Davidson, R.S. Evans, L.B. Flanagan, J.W. Munger, K. Savage, S.P. Urbanski, and S.C. Wofsy. 2006. Comparing simple respiration models for eddy flux and dynamic chamber data. Agricultural and Forest Meteorology, 141: 219-234.
Savage, K.E., Davidson, E.A., Richardson, A. and Hollinger, D., Y. 2009. Three scales of temporal resolution from automated soil respiration. Agricultural and Forest Meteorology 149, 2012–2021.
Davidson E. A., A. D. Richardson, K. E. Savage, and D. Y. Hollinger. 2006. A distinct seasonal pattern of the ratio of soil respiration to total ecosystem respiration in a spruce-dominated forest. Global Change Biology 12: 230-239.