Publications: 2005-2007     2001-2004    1996-2000    1988-1995

2007   2006   2005

2007 Publications

Gaige, E., D.B. Dail, D.Y. Hollinger, E.A. Davidson, I.F. Fernandez, H. Seivering, A. White, and W. Halteman. 2007. Changes in canopy processes following whole-forest canopy nitrogen fertilization of a mature spruce-hemlock forest. Ecosystems (2007) DOI: 10.1007/s10021-007-9081-4. (link)

An analysis of throughfall and canopy retention of ambient and experimental N (NH4NO3) addition to the forest canopy from 2004-2005.

Richardson, A.D., D.Y. Hollinger, J.D. Aber, S.V. Ollinger and B.H. Braswell. 2007. Environmental variation is directly responsible for short- but not long-term variation in forest-atmosphere carbon exchange. Global Change Biology, 13:788-803. (link)

Nine years of Howland NEE data are analyzed and used in a modeling exercise to show that at the annual time step, about 40% of the variance in modeled NEE can be attributed to variation in environmental drivers, and 55% to variation in the biotic response to this forcing.

Prabha T. V., M. Y. Leclerc, A. Karipot, and D. Y. Hollinger. 2007. Low-frequency effects on eddy-covariance fluxes under the influence of a low-level jet. Journal of Applied Meteorology and Climatology, 46:338-352. (link)

An analysis of nocturnal meteorological conditions at Howland using flux and SODAR data. The formation and breakdown of low-level jets (layers of faster moving air in the atmosphere) trigger instabilities that affect nighttime CO2 flux measurements.

2006 Publications

Davidson, E.A., I. Janssens, and Y. Luo. 2006. On the variability of respiration in terrestrial ecosystems: moving beyond Q10. Global Change Biology 12:154-164.

A review of our understanding of temperature responses of soil processes, based on our studies at Harvard and Howland forests, the coauthors’ studies, and a literature review.

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. (link)

A synthesis of measurements of chamber-based soil respiration and tower-based total ecosystem respiration at the Howland forest, showing a distinct seasonal trend in this ratio.

Gove, J. H. and D. Y. Hollinger. 2006. Application of a dual unscented Kalman filter for simultaneous state and parameter estimation in problems of surface-atmosphere exchange. J. Geophys. Res., 111, D08S07, doi:10.1029/2005JD006021. (link)

A new method of data assimilation applied to a simple carbon cycle model and flux data from the Howland forest. The method is useful for partitioning NEE into GEE and respiration, filling gaps in flux time series, and estimating model parameters.

Hagen S. C., B.H. Braswell, E. Linder, S. Frolking, A.D. Richardson, and D.Y. Hollinger. 2006. Statistical uncertainty of eddy-flux based estimates of gross ecosystem carbon exchange at Howland Forest, Maine. Journal of Geophysical Research 111, D08S03. (link)

An analysis of the uncertainties associated with partitioning measurements of net exchange to respiration and gross photosynthesis is presented using both a neural network model and a physiologically-based model. Statistical uncertainties are shown to be smaller than uncertainties associated with the choice of model.

Heinsch, F.A., M. Zhao, S.W. Running, J.S. Kimball, R.R. Nemani, K.J. Davis, P.V. Bolstad, B.D. Cook, A.R. Desai, D.M. Ricciuto, B.E. Law, W.C.Oechel, H. Kwon, H. Luo, S.C. Wofsy, A.L. Dunn, J.W. Munger, D.D. Baldocchi, L. Xu, D.Y. Hollinger, A.D. Richardson, P.C. Stoy, M.B.S. Siqueira, R.K. Monson, S.P. Burns, L.B. Flanagan. 2006. Evaluation of remote sensing based terrestrial production from MODIS using AmeriFlux eddy tower flux network observations. IEEE Transactions on Geosciences and Remote Sensing, 44: 1908-1925.

Four years of MODIS GPP estimates are compared to GPP derived from tower-based flux measurements, at 15 sites in the AmeriFlux network, including Howland.

Karipot, A; Leclerc, MY; Zhang, G; Martin, T; Starr, G; Hollinger, D; McCaughey, JH; Hendrey, GR (2006). Nocturnal CO2 exchange over a tall forest canopy associated with intermittent low-level jet activity. Theoretical and Applied Climatology, 85 (3-4): 243-248.

Loescher, H. W., B. E. Law, L. Mahrt, D. Y. Hollinger, J. Campbell, and S. C. Wofsy. 2006. Uncertainties in- and interpretation of carbon flux estimates using the eddy covariance technique. Journal of Geophysical Research 111, D21S90.

A review of fixed and random sources of uncertainty affecting the eddy covariance technique, based in part, on results from Howland.

Matross, D.M., A. Andrews, M. Pathmathevan, C. Gerbig, J.C. Lin, S.C. Wofsy, B.C. Daube, E.W. Gottleib, V.Y. Chow, J.T. Lee, C. Zhao, P.S. Bakwin, J.W. Munger, and D.Y. Hollinger. 2006. Estimating regional carbon exchange in New England and Quebec by combining atmospheric, ground-based and satellite data. Tellus 58B, 344-358. (link)

Results from the COBRA-ME project that assimilated data from a variety of sources (including Howland) to estimate regional carbon flux in the northeastern US.

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 (2006) 219-234. (link)

Howland NEE data, as well as Howland autochamber respiration data, are used to evaluate a variety of simple (no pools or feedbacks) respiration models, using objective model selection criteria (cross-validation techniques and a version of Akaike’s Information Criterion).

Richardson A. D., D. Y. Hollinger, G. G. Burba, K. J. Davis, L. B. Flanagan, G. G. Katul, J. W. Munger, D. M. Ricciuto, P. C. Stoy, A. E. Suyker, S. B. Verma, and S. C. Wofsy. 2006. A multi-site analysis of random error in tower-based measurements of carbon and energy fluxes. Agricultural and Forest Meteorology 136:1-18. (link)

Paired observations, made exactly 24 h apart and under similar environmental conditions, are used to estimate the uncertainty in measured CO2, water and energy fluxes at sites across the AmeriFlux network, including Howland. Robust patterns are shown to hold across ecosystems with similar vegetation types (e.g., forests). This work provides the foundation for incorporating uncertainty information in model-data fusion efforts.

2005 Publications

Churkina, G., D. Schimel, B.H. Braswell, X.M. Xiao. 2005. Spatial analysis of growing season length control over net ecosystem exchange. Global Change Biology, 11: 1777-1787.

An analysis, using data from 28 flux measurement sites (including Howland), of the relationship between the length of the carbon uptake period (number of days when the ecosystem is a carbon sink) and annual NEE.

Hollinger D. Y. and A.D. Richardson. 2005. Uncertainty in eddy covariance measurements and its application to physiological models. Tree Physiology 25:873-885. (link)

This paper presents an analysis of flux uncertainty based on results from two towers at Howland. This paper shows for the first time that flux uncertainties are non-Gaussian and heteroscedastic, and demonstrates how to use flux uncertainty information in Maximum Likelihood estimates of model parameters. This paper also presents a method for calculating uncertainties based on data from a single flux tower.

Lai C.-T., J.R. Ehleringer, A.J. Schauer, P.P. Tans, D.Y. Hollinger, K.T. Paw U, J.W. Munger and S.C. Wofsy. 2005. Canopy-scale d13C of photosynthetic and respiratory CO2 fluxes: observations in forest biomes across the United States. Global Change Biology, 11:633-643. (link)

An analysis of the variation in the isotopic signature of respiratory fluxes across 3 forested sites. These data are useful for estimating whole-ecosystem discrimination for 13CO2.

Richardson, A. D. and D. Y. Hollinger. 2005. Statistical modeling of ecosystem respiration using eddy covariance data: Maximum likelihood parameter estimation, and Monte Carlo simulation of model and parameter uncertainty, applied to three simple models. Agricultural and Forest Meteorology 131: 191-208. (link)

Using three different respiration models as a case study, the use of flux measurement uncertainty information in conducting maximum likelihood parameter estimation, and running Monte Carlo simulations, is demonstrated. The uncertainty in annual sums of modeled ecosystem respiration at Howland is found to be less than ±40 g C m-2 y-1 at 95% confidence.

Sims D.A., Abdullah F. Rahman, Vicente D. Cordova, Dennis D. Baldocchi, Lawrence B. Flanagan, Allen H. Goldstein, David Y. Hollinger, Laurent Misson, Russell K. Monson, Hans P. Schmid, Steven C. Wofsy, and Liukang Xu. 2005. Midday values of gross CO2 flux and light use efficiency during satellite overpasses can be used to directly estimate eight-day mean flux. Agricultural and Forest Meteorology 131:1-12. (link)

A synthesis of results from 8 AmeriFlux sites (including Howland) showing that light-use efficiencies calculated at midday every 8 days (the time and frequency of the MODIS sensor satellite overpass) was sufficient to model GPP over that timespan.

Xiao X., Q. Zhang, D. Hollinger, J. Aber, and B. Moore III. 2005. Modeling seasonal dynamics of gross primary production of an evergreen needleleaf forest using MODIS images and climate data. Ecological Applications, 15:954-969. (link)

A model of GPP driven by climate and MODIS data was developed for coniferous forest based on Howland flux data.

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