Disturbance dynamics and history of an old-growth subalpine fir (Abies fargesii) forest in central China

Disturbance history of an old-growth subalpine fir (Abies fargesii) forest in the Shennongjia Mountains of central China was reconstructed using dendroecological methods. Increment cores were extracted from 468 trees within six 100 m × 50 m permanent transects distributed across the old-growth subalpine fir forest of 300 ha. Growth patterns of 299 fir cores were examined for abrupt increases in radial growth to indicate formation of past canopy gaps and for rapid early radial growth to indicate establishment in past canopy gaps. The results showed that 70.8 % of the canopy fir trees experienced an average of 0.78 (ranging from 0 to 2) major release event for an average of 15.8 (ranging from 10 to 24) years, and an average of 1.94 (ranging from 0 to 3) moderate release events for an average of 25.6 (ranging from 10 to 36) years before they reached canopy. Recruitment pulse of trees coincided temporally with the peak of disturbance rate from the 1900s to the 1910s, suggesting occurrence of intense disturbance events during the time period. Radial growth analyses indicated that a history with small-scale disturbance events has resulted in the formation of the old-growth subalpine fir forest, and stand-replacing disturbances might not be necessary for the development of the forest. This study provides strong evidence that there are substantial variations in the disturbance severity and frequency over time. Most disturbance events might rather cause treefall gaps than clear large areas of forest at once. Thus, the old-growth subalpine fir forest experienced frequent gap-scale disturbances and few large-scale disturbances in its development history.