Forest ecosystems play a significant role in sequestering carbon (C) in biomass and soils. Plantations established in subtropical China since the 1980s, mainly of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) in monocultures, have proved to be major C sinks. However, information is lacking about whether mixing Chinese fir with broadleaved tree species will increase stand growth and C sequestration. We address this question by comparing a pure Chinese fir plantation and two mixed plantations established in 1990 at Huitong Experimental Station of Forest Ecology, Hunan Province, China. The mixed plantations include Chinese fir and either Kalopanax septemlobus (Thunb.) Koidz or Alnus cremastogyne Burk., planted at 4:1 ratios. We found that total C storage was 123, 131 and 142Mgha⁻¹ in the pure plantation, mixed plantation with K. septemlobus, and mixed plantation with A. cremastogyne, respectively. The mixed plantation with A. cremastogyne increased C storage in biomass relative to the pure Chinese fir plantation (P <0.05). No significant difference was detected between mixed plantations. Soil C storage did not differ among these plantations, ranging from 67.9±7.1 to 73.3±9.1Mgha⁻¹, which accounted for about 55% of the total C pools. Our results indicated that as the mixture of Chinese fir and broadleaved species will increase both biomass C and soil C storage over pure Chinese fir, and will do it, within 15 years of planting.
