Measurements of radiation and energy balances were made over two forests, 12.8 km apart, in eastern Ontario during three summers, 1989-1991. The two sites were AECL, a primarily deciduous forest with fine sandy soils, and PNFI, a mixed forest over a thin sandy-loam soil. The objective of the study was to investigate spatial heterogeneity in energy fluxes in a mixed forest landscape by examining interannual variations in radiation and energy balance components between the sites. The two sites showed small differences in albedo and net radiation. Total heat storage was not different between the two sites, yet there were some differences in the relative magnitudes of the storage components. The largest between-site differences were in energy partitioning between the convective fluxes of sensible heat,QH, and latent heat,QE. TheQHwas usually larger at PNFI andQEwas usually larger at AECL. Thus, Bowen ratios were almost always smaller at AECL. The magnitude of these differences was controlled by soil moisture stress, with moisture stress frequently observed at PNFI but not at AECL. The implications of these results for regional-scale surface-vegetation-atmosphere climate modelling are discussed.