Spatial and temporal variation in respiration in a young ponderosa pine forests during a summer drought

Respiration rates of heterogeneous forest canopies arise from needles, stem s, roots and soil microbes. To assess the temporal and spatial variation in respiration rates of these components in a heterogeneous ponderosa pine fo rest canopy, and the processes that control these fluxes, we conducted an i ntensive field study during the summer of 2000. We employed a combination o f biological and micrometeorological measurements to assess carbon respirat ory fluxes at the soil surface, within and above a 4-m-tall ponderosa pine forest. We also conducted manipulation studies to examine the carbon fluxes from the roots and heteorotrophs. Spatial variation in Soil CO2 efflux was large, averaging 40% of the mean, which varied by nearly a factor of two between minima for bare soil to maxi ma beneath dense patches of understorey vegetation. The estimated vertical profile of respiration from chamber data, and the profile of nocturnal flux es measured by the three eddy flux systems suggested that > 70% of the ecos ystem respiration was coming from below the 1.75-m measurement height of on e of the flux systems, and 71% of photosynthetic carbon uptake in July was released by soil processes, thus there was a strong vertical gradient in re spiration relatively close to the soil surface in this young forest. These results stress the importance of understanding spatial and temporal variati on in soil processes when interpreting nocturnal eddy covariance data. (C) 2001 Elsevier Science B.V. All rights reserved.