Quantitative assessment of carbon (C) storage by forests requires an understanding of climatic controls over respiratory C loss. Ecosystem respiration can be estimated biometrically as the sum of soil, leaf, and wood respiration, and meteorologically by measuring above-canopy nocturnal CO2 fluxes. Here we estimated respiratory sum over 5 year in a forest in Michigan, USA, and compared respiratory sum and above-canopy nocturnal CO2 fluxes on turbulent nights. We also evaluated forest cabon-use efficiency using biometric estimates of net primary production and respiratory sum and above-canopy nocturnal CO2 fluxes-derived estimates of gross primary production. Interrannual variation in respiratory sum was modest (142 g C/m2/yr). Mean annual respiratory sum was 1425 g C/m2/yr; 71% from soil, 18% from leaf, and 11% from wood. Hourly respiratory sum was well correlated with above-canopy nocturnal CO2 flux, but 11 to 58% greater depending on the time of year. Greater respiratory sum compared with above-canopy nocturnal CO2 flux resulted in higher estimated annual gross primary productivity and lower annual forest carbon-use efficiency (0.42 vs 0.54) using biometric and meteorological data, respectively. Our results provide one of the first multiyear estimates of respiratory sum in a forested ecosystem, and document the responses of component respiratory C losses to major climatic drivers. They also provide the first assessment of forest carbon use efficiency in a deciduous forest using independent estimates of gross primary production.