Ecosystem respiration in a young ponderosa pine plantation in the Sierra Nevada Mountains, California

We estimated total ecosystem respiration from a ponderosa pine (Pinus ponde rosa Dougl. ex Laws.) plantation in the Sierra Nevada Mountains near George town, California, from June to October, 1998. We apportioned ecosystem resp iration among heterotrophic, root, stem and foliage based on relationships for each component that considered microclimate and vegetation characterist ics. We measured each respiration component at selected sampling points, an d scaled the measurements up to the ecosystem based on modeled relationship s. Over the study period, total mean ecosystem respiration was 5.7 +/- 1.3 mu mol m(-2)s(-1)(based on daily mean), comprising about 67% from soil-surf ace CO2 efflux, 10% from stem and branch respiration and 23% from foliage r espiration. Shrub leaves contributed about 24% to total foliage respiration , and current-year needles (1998 age class) accounted for 40% of total tree needle respiration. Root respiration accounted for 47% of soil-surface CO2 efflux. We conclude that ecosystem respiration can be estimated based on d aily mean air and soil temperatures through exponential relationships with r(2) values of 0.85 and 0.87, respectively. When based on both air and soil temperatures, about 91% of the variation in total ecosystem respiration co uld be explained by a linear regression.