Cunninghamia lanceolata sprout population structure, dynamics and biomass allocation changes during Phyllostachys edulis expansion in middleo-southern China

Key message Chinese fir sprouting population lifespan is shortened and survivorship situation and biomass are also changed by bamboo expansion via declines in mother tree density and weakened physiological accommodation. Natural regeneration is a vital means of maintaining forest populations. Although bamboo expansion negatively affects population structures of neighboring communities, its influence on sprouting natural regeneration is still poorly understood. We compared the population structure and biomass allocation of Chinese fir regenerating sprouts in previous (CLS), middle (CPM) and late (PCM) periods of bamboo expansion. Life tables and survivorship curves were used to assess sprouting population structure and survival dynamics, and allometric analysis was conducted on biomass allocation. The results showed that bamboo expansion reduced the number and longevity (maximum age class shorted from X to VI) of the Chinese fir sprouting population and weakened its survival capacity. Survivorship curves indicated that the CLS population conformed more to a recession type (Deevey III) while CPM and PCM tended to be stable types (Deevey II). Highly mortality and survival risk in the early growing stage drove a population decrease. Meanwhile, sprouting component biomasses were decreased first and then increased by expansion effect, leaf and stem biomass had constant relationships with total biomass, and branch biomass had allometric relationships with total biomass. We considered that bamboo expansion changed sprouting population survival and growth mainly through affected Chinese fir mother tree density and growth.