Production and turnover of fine roots of mature Douglas-fir in relation to site

Fine roots are a dynamic component of Douglas-fir ecosystems.Changes in standing crops indicate that fine roots require a majorportion of the stand's energy resources to fulfill their role in thefunctioning of these systems. We observed standing crops of live anddead fine ( necessarily correspond to changes in standing crop, indicating thatfine—root growth and mortality can occur simultaneously in the samearea. Based on a simple conceptual model of fine—root dynamics weestimated fine—root production and turnover by inferring transfersneeded to account for observed standing crops of live and dead fineroots. When averaged over the entire study period, we estimate fine—root growth as 6.5, 6.3, and 4.8 Mg/ha/yr, fine—root mortality as 7.2,7.2, and 5.5 Mg/ha/yr, and decomposition of fine roots as 8.2, 8.0,and 6.9 Mg/ha/yr for the dry, moderate, and wet sites, respectively.These values are 3-5 times greater than foliage litterfall. Thus fineroots constitute a major sink of carbohydrates and source of detritusfor the belowground ecosystem.