We examined how rapidly soils can change during secondary succession by observing soil development on 350-year chronosequences in three pristine forest ecosystems in southeast Alaska. 2 Soil surfaces, created by different windthrow events of known or estimated age, were examined within each of three forest stands (0.5-2.0 ha plots; i.e., a within-stand chronosequence method). Soil surfaces are more likely to have developed under common climate and vegetation conditions within stands than in the spatially separated ecosystems used in traditional chronosequence studies. 3 We observed rates of change that were higher than those previously reported for secondary succession, and were similar to those described for primary succession. Well-developed spodic and albic (podzol) horizons with characteristic C, Fe, and Al signatures were found in soil surfaces less than 150 years old. Carbon accumulated linearly at 21 g m-2 yr-1 ; mineral P and N became increasingly immobilized in the spodic horizon as time passed. We found no trend toward an equilibrium in C or N accumulation over the 350-year chronosequences in any of the three stands examined. 4 These rapid changes in soil and a shift in rooting from mineral to organic horizons appeared likely to reduce productive capacity of the soil during a single generation of trees. Windthrow or disturbances that mimic windthrow may be required at intervals of about 200-400 years to maintain soil productive capacity in these ecosystems.

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