Canopy gap area/age distributions and growth mechanisms were examined in a virgin subalpine forest in the White Mountains, New Hampshire, USA. The gap area distribution was negative exponential in form. Whithin gap tree ages varied widely in response to stepwise gap expansion caused by windthrow of peripheral trees or death of standing mature Picea rubens at gap edges. As a consequence, the density of small gaps may have been underestimated and the density of large gaps overestimated. The estimates of canopy turnover time, 303 yr, and of patch birth rate on an area basis, 3.3×10^-3 ha new patches/ha land area/yr, were not affected by the gap expansion phenomenon. However, any estimate of patch birth rate as numbers of new patches formed per year would have been too low. Because of increasingly widespread Picea death, the patch area/age distribution of this forest may not currently be in steady-state.