Woody tissue maintenance respiration of four conifers in contrasting climates

We estimate maintenance respiration for boles of four temperate conifers (ponderosa pine, western hemlock, red pine, and slash pine) from CO₂ efflux measurements in autumn, when construction respiration is low or negligible. Maintenance respiration of stems was linearly related to sapwood volume for all species; at 10°C, respiration per unit sapwood volume ranged from 4.8 to 8.3 μmol CO₂ m^-3 s^-1. For all sites combined, respiration increased exponentially with temperature (Q₁₀=1.7, r²=0.78). We estimate that maintenance respiration of aboveground woody tissues of these conifers consumes 52-162 g C m^-2 y^-1, or 5-13% of net daytime carbon assimilation annually. The fraction of annual net daytime carbon fixation used for stem maintenance respiration increased linearly with the average annual temperature of the site.