In collaboration with Drs. Allen Goldstein and Dennis Baldocchi of UC Berkeley, we have been investigating the interactive relationship between vegetation aboveground and processes belowground both at a ponderosa pine plantation near Blodgett Forest Station in the Eastern Sierras and at an oak-savanna site at the lower foothills of the Sierra Nevada Mountains near Ione, California . The research sites have been instrumented with Eddy towers monitoring stand-level gas exchange and minirhizotrons for measuring root dynamics. The main objective has been to investigate how the aboveground activities control root turnover and carbon fluxes belowground. Here are some of the highlights of the results so far: (1) At the ponderosa pine site, the average ratio of root over total respiration was 0.56 during the growing season and 0.16 during the non-growing season with an annual average of 0.44, a value very close to the medium estimates for temperate forests. (2) The only significant factor that dictated fine root growth at Blodgett in the spring was the increase of soil temperatures above the daily minimum of 5 ºC, and the only significant factor that dictated the end of root production is soil moisture dropping below 17%, indicating that the time window for root growth is extremely narrow at the site because of the low soil temperature during winter and long period of water stress during summer. (3) This especially narrow time window for root growth is a unique aspect of the Western Sierra forests, as compared to some other temperate forests, and ascribes to the high level of disconnect between aboveground activities and belowground rhizosphere processes. (4) The largest variation in soil respiration at the site occurred due to an increase in heterotrophic respiration after episodic rain events during the normally dry summer.