Regeneration dynamics of subalpine fir (Abies fargesii) forest across the altitudinal range in the Shennongjia Mountains, central China

Age structure and regeneration dynamics have been used to infer population response to environmental events and reconstruct forest development history. The aim of this study was to characterize and examine the differences of the age structure and regeneration dynamics of subalpine fir (Abies fargesii) forest across the altitudinal range in the north and south aspects in the Shennongjia Mountains, central China. Ten plots (2020 m) at each altitudinal zone (i.e. the low elevation, the middle elevation and the high elevation) were established in both the north and south aspects of the Shennongjia Mountains, central China. Dendroecological techniques were applied to obtain information about ages of the trees in the plots. The population age structure was analyzed to investigate the regeneration dynamics across the altitudinal range. Fir regeneration dynamics and age structure were similar in both aspects, and a unimodal population age structure was found at different altitudinal sites of both aspects, indicating that environmental factors might play an important role in shaping the regeneration dynamics and age structure of A. fargesii across its altitudinal range. There was a sustained recruitment during the 19th century, but the regeneration was rarer in the last century at low and midelevations. A significant greater number of fir seedlings and saplings recruited at high elevations in the last century, and fir tree density at high elevations was significantly higher than that at low elevations. Thus, the fir population at the high elevations showed a significant increase in recruitment and stem density in the last century, and we propose that the gradual infilling of fir seedlings might result in changes in regeneration dynamics and stand structure of the subalpine fir forest at high elevations in the Shennongjia Mountains, central China.