For the last several decades, native broad-leafed forests in many areas of south China have been converted into plantations of more productive forest species for timber use. This paper presents a case study examining how this forest conversion affects ecosystem carbon storage by comparing 33 year-old plantations of two coniferous trees, Chinese fir (Cunninghamia lanceolata, CF) and Fokienia hodginsii (FH) and two broadleaved trees, Ormosia xylocarpa (OX) and Castanopsis kawakamii (CK), with an adjacent relict natural forest of Castanopsis kawakamii (NF150 year old) in Sanming, Fujian, China. Overall estimates of total ecosystem carbon pools ranged from a maximum of 399.1 Mg ha-1 in the NF to a minimum of 210.6Mg ha-1 in the FH. The combined tree carbon pool was at a maximum in the NF where it contributed 64% of the total ecosystem pool, while the OX had the lowest contribution by trees at only 49%. Differences were also observed for the carbon pools of undergrowth, forest floor and standing dead wood, but that these pools together represent at the most 5% of the ecosystem C stock. Total C storage in the surface 100cm soils ranged from 123.9Mg ha-1 in the NF to 102.3Mg ha-1 in the FH. Significant differences (P<0.01) in SOC concentrations and storage between native forest and the plantations were limited to the surface soils (0-10cm and 10-20cm), while no significant difference was found among the plantations at any soil depth (P>0.05). Annual aboveground litterfall C ranged from 4.51Mg ha-1 in the CK to 2.15Mg ha-1 in the CF, and annual belowground litterfall (root mortality) C ranged from 4.35 Mg ha-1 in the NF to 1.25Mg ha-1 in the CF. When the NF was converted into tree plantations, the vegetation C pool (tree plus undergrowth) was reduced by 27-59%, and the detritus C pool (forest floor, standing dead wood, and soils) reduced by 20-25%, respectively. These differences between the NF and the plantations may be attributed to a combination of factors including more diverse species communities, more C store types, higher quantity and better quality of above-and belowground litter materials under the NF than under the plantations and site disturbance during the establishment of plantations.

杉木（Cunninghamia lanceolata）是我国南方最主要的造林树种之一，由于其速生丰产，在我国南方林区得到很大的发展，但随着连栽代数不断增加，地力衰退日趋严重［1-3］。我国南方用于造林的主要树种大多集中于杉木、马尾松等有限的几个树种，出现了杉木连栽地力衰退及杉木用途的受限等问题，因此，寻找速生丰产又能维持地力的造林树种，在一定范围内替换杉木，已成为南方林区实现林地可持续经营的重要措施之一。福建柏（Fokienia hodginsii Henry et Thomas），又称建柏，是我国的特有种，树形美观，树干通直，生长快，材质好，具有较高的经济、生态和美学价值［］。各地造林实践和研究报道认为，在中等或较差的立地条件下，福建柏的生长速度可以超过杉木［4-6]，而福建柏与杉木、檫树、樟树树等组成混交林还可促进目的树种的生长［］。本课题组自1999 年起，选择莘口教学林场1967 年在小湖工区营造的较大面积的福建柏和杉木人工林，对两种林分的凋落物和细根特性，凋落物和细根分解及养分释放过程，C 吸存与流动及树种自我培肥地力能力等进行了系统研究。通过对福建柏和杉木人工林生物学与生态学特性差异进行比较，试图为探讨福建柏在一定范围内替换杉木的潜力提供理论依据。

通过对福建三明36a生的格氏栲人工林和杉木人工林林木地下C分配（TBCA）进行研究，结果表明，由分室累加法直接测定的格氏栲和杉木人工林的TBCA分别为8.426 和4.040tC·hm-2·a-1。在格氏栲和杉木人工林TBCA组成中，根系净生产量和根系呼吸各约占50%；在根系年净生产量中，细根年净生产量和粗根年净生产量各约占75%和25%。而格氏栲和杉木人工林的细根年C归还量则均约占各自TBCA的1/3（分别为33%和36%）。在假设地下C库处于稳定状态时，由C平衡法计算的格氏栲和杉木人工林的TBCA（分别为6.039 和2.987tC·hm-2·a-1）低于分室累加法，这与两种人工林地下C库尚未达到稳定状态有关。利用Raich and Nadelhoffer（1989）全球模式方程推算的格氏栲和杉木人工林的TBCA（分别为9.771和5.344tC·hm-2·a-1）则高于分室累加法，这与全球模式方程只是一种全球尺度规律有关。

ed in Yizhou work area of Yizhou state Forestry Centre in Fujian Province, China, were examined following slash burning to compare nutrient capital and topsoil properties with preburn levels. After fire, nutrient (N, P and K) removal from burning residues was estimated at 302.5 kg ha-1 in the CF and 644.8 kg ha-1 in the EB. Fire reduced the topsoil capitals of total N and P by ～20% and ～10%, respectively in both forests. While K capital was increased in the topsoils of both forests following fire. Total site nutrient loss through surface erosion was 28.4kg (N) ha-1, 8.4kg (P) ha-1 and 328.7kg (K) ha-1 in the CF. In the EB, the losses of total N, P and K were 58.5, 10.5 and 396.3kg ha-1, respectively. Improvement of soil structure and increase in mineralization of nutrients associated with increased microbe number and enzyme activities and elevated soil respiration occurred 5 days after fire. However, organic matter and available nutrient contents and most of other soil parameters declined one year after fire on the burned CF and EB topsoils. These results suggest that short-term site productivity can be stimulated immediately, but reduced subsequently by soil and water losses, especially in South China, where high-intensity precipitation, steep slopes and fragile soil factor can be expected. Therefore, the silvicultural measurements should be developed in plantation management.

本文研究了福建三明27年生杉木观光木混交林和杉木纯林群落细根（d<2mm）的生产力、分布和养分归还。结果表明，混交林细根生物量、N、P 养分现存量分别为5.381thm-2、48.085kghm-2和4.174kghm-2，分别比杉木纯林的增加17.4%、27.2%和20.0%。混交林细根的年净生产力达4.124 t hm-2 a-1，比纯林高出16.9%。混交林杉木和观光木细根均在表层土壤富集，而在较深层土壤两者分布具镶嵌性；与混交林杉木相比，纯林杉木土壤表层细根量较少，最大分布层次下移。混交林中观光木细根的周转速率为1.16，杉木为0.96；而林下植被层细根周转速率（1.46～1.52）均高于相应的乔木层。混交林细根的年死亡量、N和P养分年归还量分别达2.119thm-2、18.559kghm-2和1.565kghm-2，分别是纯林的1.21倍、1.23倍和1.14倍，其中林下植被细根占有较为重要位置。对细根分布与土壤性质的相关分析表明，细根的垂直分布与土壤全N的相关性最强（0.87～0.89）。