Agricultural and Forest Meteorology 156 (2012) 75–84 Contents lists available at SciVerse ScienceDirect Agricultural and Forest Meteorology jou rn al h om epa g e: www.elsevier.com/locate/agrformet Estimating the net ecosystem exchange for the major forests in the northern United States by integrating MODIS and AmeriFlux data Xuguang Tang a,b , Zongming Wang a , Dianwei Liu a,∗ , Kaishan Song a , Mingming Jia a , Zhangyu Dong a , J. William Munger c , David Y. Hollinger d , Paul V. Bolstad e , Allen H. Goldstein f , Ankur R. Desai g , Danilo Dragoni h , Xiuping Liu i a Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences, Changchun 130012, China b Graduate University of Chinese Academy of Sciences, Beijing 100049, China c Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA d US Forest Service, Northern Research Station, Durham, NH, USA e Department of Forest Resources, University of Minnesota, St. Paul, MN, USA f Department of Environmental Sciences, Policy, and Management, University of California, Berkeley, CA, USA g Department of Atmospheric and Oceanic Sciences, University of Wisconsin, Madison, WI, USA h Department of Geography, University of Indiana, Bloomington, IN, USA i Key Laboratory of Agricultural Water Resources, Hebei Key Laboratory of Agricultural Water-Saving, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China a r t i c l e i n f o Article history: Received 21 April 2011 Received in revised form 21 December 2011 Accepted 3 January 2012 Keywords: NEE Eddy covariance MODIS EVI LST LSWI a b s t r a c t The eddy covariance technique provides long-term continuous monitoring of site-specific net ecosystem exchange of CO 2 (NEE) across a large range of forest types. However, these NEE estimates only represent fluxes at the scale of the tower footprint and need to be scaled up to quantify NEE over regions or conti- nents. In the present study, we expanded a method developed previously and generated a new NEE model exclusively based on the Moderate Resolution Imaging Spectroradiometer (MODIS) products, including enhanced vegetation index (EVI), land surface water index (LSWI), land surface temperature (LST) and Terra nighttime LST ′ . This method, in our previous research, provided substantially good predictions of NEE and well reflected the seasonal dynamics of the deciduous broadleaf forest at the Harvard forest site. Studying NEE of forests in the middle-latitude regions of the Northern Hemisphere is significant because it may help to understand the ‘missing carbon sink’ from terrestrial ecosystems. In this study we selected eight eddy flux sites to represent the major forest ecosystems in the northern United States. Compared with the model based on a single site, we also established the general models that apply to evergreen needleleaf forest (ENF) and deciduous broadleaf forest (DBF), respectively. The results showed that our simpler model based entirely on MODIS products promised well to estimate NEE by the eddy covariance technique. The modeled annual mean NEE from DBF deviated from the measured NEE by 44.4%, whereas the modeled NEE from ENF was extremely close to the measured NEE within 5.5%. In the end, we also validated both general models for ENF and DBF using independent flux sites. It demonstrated this method performed well for estimating NEE. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Effects by forest ecosystem play a significant role in the global carbon cycle and help to mitigate atmospheric increases due to fossil fuel emissions (Schimel, 1995; Schimel et al., 2001; Alley et al., 2007). Net ecosystem carbon exchange (NEE), the balance between photosynthetic uptake and release of carbon dioxide by respiration from autotrophs and heterotrophs, represents the ∗ Corresponding author. Tel.: +86 43185542364; fax: +86 43185542299. E-mail address: dianweiliu@gmail.com (D. Liu). carbon sequestration between terrestrial ecosystems and the atmosphere during a given period. An accurate estimation of the spatial patterns and temporal dynamics of NEE in terrestrial ecosystems at the regional and global scale is of great interest to human society and is necessary for understanding the carbon cycle of the terrestrial biosphere (Xiao et al., 2010, 2011). The temperate forests of the Northern Hemisphere have been identified as an important sink for storing atmospheric CO 2 with annual uptake values ranging between 70 and 870 g C m -2 year -1 (Baldocchi et al., 2001; Law et al., 2002). Despite the consensus that the middle-latitude regions of the Northern Hemisphere are presently functioning as a carbon sink, the size and distribution of 0168-1923/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.agrformet.2012.01.003