广西马山岩溶次生林群落生物量和碳储量

Biomass and carbon storage of communities in secondary karst forests in Mashan county,Guangxi

岩溶植被在岩溶生态系统碳循环和全球碳平衡中具有重要的作用。通过对马山县岩溶次生林年龄序列(幼龄林、中龄林和老龄林)3个演替阶段9个样地(20 m×50 m)的系统取样调查,研究了停止人为干扰后岩溶次生林生物量和碳储量的变化。结果表明:沿幼林、中林和老林群落的顺向演替发展,群落生物量显著增加(P<0.05),从幼林群落的48.17 t/hm2、到中林群落113.47 t/hm2,再到老林群落242.59 t/hm2。老林生态系统的碳储量较高,平均为236.69 t/hm2,中林和幼林较低且非常相近,分别为225.17 t/hm2和224.76 t/hm2,各次生林生态系统的碳储量差异不显著(P>0.05)。土壤碳储量的大小顺序为幼林(198.44 t/hm2)>中林(167.39 t/hm2)>老林(113.43 t/hm2)。沿群落正向演替,各次生林生态系统中植物碳储量和土壤碳储量的比例发生明显的变化。幼林的土壤碳储量占生态系统碳储量的88.29%,植物碳储量只占11.71%;中林相应为74.34%和25.66%;而老林为47.92%和52.08%。可见,随着岩溶植被的正向演替,土壤碳转变为植物碳的趋势十分明显,这是岩溶森林不同于酸性土森林的一个显著特征。

Karst vegetation plays an important role in the karst ecosystem carbon cycle and the global carbon balance. However, most of the estimations on biomass and carbon sequestration patterns for many karst forest vegetation ecosystems were questionable. The lack of accurate characterization of carbon storage in tree, understory, forest floor and organic soil layers in karst forest vegetation ecosystems has hindered the effort to estimate their contribution to the global carbon stocks. In this study, we investigated changes in biomass and carbon storage of karst vegetation along successional stages of a chronosequence following human disturbance in Mashan county, southwest China. We sampled nine plots, each of 20 mx50 m, three of which represented successional stages of young, mid-mature and old forest, respectively. We found that community biomass increased significantly along the successional stages, from 48.17 t/hm2 in young forest to 113.47 t/hm2 in mid-mature forest to 242.59 t/hm2 in old forest （P 〈 0.05 ）. The biomass of the understory vegetation in different successional stages is very low, accounting for 4.32%, 1.47% and 0.47% of the total biomass in communities of young, mid-mature, and old forsts, respectively. The mean biomass carbon storage in old forests （123.26 t/hm2） was significantly higher than that in young forest （26.32 t/hm2） and than that in mid-mature forest （57.78 t/hm2） （P 〈0,05）, and it was significantly higher in mid-mature forests than that in young forests （P 〈0.05）. Carbon storages in tree and herb layers were significantly different among the three forest types （P 〈0.05）. The differences in carbon storage in shrub layer, however, was not significantly different among the three forest types （P 〉 0.05）. Carbon storage in forest floor litter in mid-mature forest （0.20 t/hm2） was significantly lower than that in young forest （1.19 t/hm2） and in old forest （1.40 t/hm2）. Soil carbon storage was significantly different between old forest （113.43 t/hm2） and young forest （198.44 t/hm2）, but the difference in soil carbon was not significant between old forests and mid-mature forests （167.39 t/hm2）. In all three forest types, carbon storage in soil decreased as depth increased. Overall, carbon storage in old forest ecosystems （236.69 t/hm2） was only slightly higher than that in young forest （ 224.76 t/hm2 ） and mid-mature forest （ 225.17 t/hm2 ）, but these differences were not statistically significant （P 〉 0.05）. In contrast, soil carbon storage was highest in the young forest （198.44 t/hm2） , followed by mid-mature forest （167.39 t/hm2） and old forest （113.43 t/hm2）. The ratios of plant vs. soil carbon storage in various secondary forest ecosystems increased significantly along the successional stages. The percentages of plant and soil carbon storage were 11.71% and 88.29%, respectively, in young forest ecosystems, 25.66% and 74.34% in mid-mature forest, and 47.92% and 52.08% in old forest. It appeared that soil carbon was converted to plant carbon as forest moving forward along the successional chronosequence in the karst region. Our results suggested that the carbon storage capacity of the karst forest ecosystems decreased due to the.high bare rock cover, limited soil cover, shallow soil layer, and low biomass. Our results also indicated that the carbon sequestration and carbon allocation in the karst ecosystems were influenced strongly by karst forest vegetation succession. More long-term monitoring and research are needed to further evaluate biomass and carbon accumulation of the karst forest vegetation succession.