Woods Hole Research Center

Scientist Dave Hollinger takes a core from a tree to establish its age.

Led by colleagues David Hollinger (USDA-FS) and Andrew Richardson (Harvard University), WHRC scientists and collaborators have been measuring whole ecosystem carbon exchange using the eddy covariance technique since 1995. The eddy covariance technique measures the net exchange of carbon (NEE) between the forest ecosystem (trees and soils) and the atmosphere. As the second-oldest operating site within the AmeriFlux network, Howland data provide a valuable perspective on long-term trends and decadal-scale variability in forest C cycling.

WHRC scientists also measure forest biomass, and the composition of the biomass as part of our carbon sequestration measurements. These biomass estimates are compared to eddy covariance (NEE) measurements and used to constrain carbon exchange from different ecosystem components, such as trees, soils, and deadwood.

Methods and Measurements

Long Term Study Plots-Main Tower: There are 5 long term study plots, each with 8 collars per location, along a drainage gradient within the footprint of an eddy covariance tower. Soil respiration and soil temperature are measured at weekly intervals in the summer, and bi-monthly to monthly during the spring, fall, and winter seasons. Soil respiration is measured using a dynamic chamber system described in more detail below. Soil temperature is measured using type T thermocouple wire at 10cm depth, concurrent with soil respiration measurements.

Results

• This mature, unmanaged forest is still vigorously accumulating carbon. The average net ecosystem C sequestration during the last decade was 1.85 Mg C ha-1 y-1, although considerable year-to-year variation in sink strength is evident.
• Warmer than normal spring temperatures lead to enhanced carbon sequestration while warmer temperatures in the autumn lead to higher carbon losses.
• A unique two-tower design showed that flux towers make representative and repeatable measurements of forest carbon exchange. Most of the C storage (about 1.6 Mg C ha-1 y-1 can be accounted for in the live biomass.

Key Publications

Richardson. AD, Williams M, Hollinger DY, Moore DJP, Dail DB, Davidson EA, Scott NA, Evans, RS, Hughes H, Lee JT, Rodrigues C, and Savage K. 2010. Estimating parameters of a forest ecosystem C model with measurements of stocks and fluxes as joint constraints. Oecologia, DOI10.1007/s00442-010-1628-y.

Hollinger DY, Aber J, Dail B, Davidson EA, Goltz SM, Hughes H, Leclerc M, Lee JT, Richardson AD, Rodrigues C, Scott NA, Varier D, Walsh J. 2004. Spatial and temporal variability in forest-atmosphere CO2 exchange. Global Change Biology 10:1689-1706.

Hollinger, D. Y.; Richardson, A. D. 2005. Uncertainty in eddy covariance measurements and its application to physiological models. Tree Physiology 25: 873– 885.