Disentangling the effects of stand and climatic variables on forest productivity of Chinese fir plantations in subtropical China using a random forest algorithm

•Forest productivity is affected by age, BA, Hd, Gini, and four climate factors.•Young forests are more resistant to climate conditions.•Productivity in stands with middle-high competition was similar, but less than low competition.•Higher SMMT, AP and lower AHM enlarge the productivity gap in different stand conditions.•Site conditions had little effect on forest productivity while AP< 1250 mm.