Estimation of daytime net ecosystem CO2 exchange over balsam fir forests in eastern Canada: combining averaged tower-based flux measurements with remotely sensed MODIS data

Abstract

The focus of this paper is to develop a practical approach for estimating daytime net CO2 fluxes (i.e., daytime net ecosystem exchange or NEE) generated over balsam fir (Abies Balsamea (L.) Mill.) dominated forest ecosystems in the Atlantic Maritime ecozone of eastern Canada. The approach establishes empirical relationships between daytime NEE and absorbed photosynthetically active radiation (APAR) for the May–September period in 2004 and 2005 using flux measurements obtained at one of four flux towers in west-central New Brunswick, Canada. Our analysis reveals that the seasonally averaged daytime NEE and APAR values are strongly correlated. A linear regression fitted to the data explains more than 97% of the variation in the averaged daytime fluxes. Application of this linear relationship to data collected from a second New Brunswick flux site with higher measured NEE produces an equally high r2 value (~99%) when a linear fit is applied to the observed versus predicted values. Spatial calculations of APAR are obtained by multiplying the moderate resolution imaging spectroradiometer (MODIS) derived fraction of photosynthetically active radiation and digital elevation model corrected calculations of photosynthetically active radiation. This information and the relationship between daytime NEE and APAR provide the basis for the calculation of NEE across a balsam fir dominated region in northern New Brunswick, where it constitutes more than 50% of the forest cover.