| Foliar respiration forms a large component of the carbon balance of any coniferous forest. We examine seasonal, interannual, spatial and interspecific variation of foliar maintenance respiration in a forest in Washington, USA, with measurements made quarterly for >4 years on ∼400-year old trees of Pseudotsuga menziesii, Tsuga heterophylla and Thuja plicata. Most variation is related to temperature, as well as to canopy position and to non-temperature related seasonal effects. Interannual variation is sometimes significant even after taking into account differences in measurement temperatures, suggesting that scaled-up, stand-level canopy respiration may vary significantly between years.; Scaling respiration from the leaf to the stand requires canopy leaf area index (LAI) for each species in each season at each canopy level. Thorough LAI data are available at one time of year (late August). We use a five-year record of monthly leaf litter data to determine changing seasonal LAI for each species at each canopy level. Collected litter leaves are related to monthly changes in live leaf area, then combined with the "standing crop" direct measurements of live LAI from August. Maximum stand LAI (9.05) is 37% greater than the minimum (6.63). Most leaf loss occurs from July-September, earlier than for conifers elsewhere in the world but coinciding with the regional dry season, suggesting that early leaf loss is a drought response.; Values of respiration are scaled to the stand to yield nighttime foliar respiration by conifers, using a respiration-temperature model, with micrometeorological and LAI data. Variation is included using a probability-distribution model for respiration and temperature for the leaf-level measurements, and of air temperatures. Values are found of total foliar maintenance respiration in four consecutive years. The four-year mean is 3.40 x 106 g C ha-1 y-1, with minor interannual differences. Annual carbon investment for new leaf construction is 1.70 x 106 g C ha-1 y-1, meaning that construction and maintenance of leaves may utilize ∼1/3 of conifer gross primary productivity. Three recent papers producing divergent estimates regarding the carbon economy of the same forest are brought into closer agreement through substitution of certain results of this study. |
