Seasonal Dynamics of Energy Return Through Litterfall of A Mixed Forest of Chinese Fir and T. odorum

Based on the measurement of monthly litterfall and their gross calor ic values, the seasonal dynamics of energy return through litterfall were determ ined in a pure and a mixed T. odorum (Tsoongiodendron odorum Chun) forests with Ch inese fir (Cunninghamia lanceolata (Lamb.) Hook.) in Sanming, Fujian Provinc e. Annual ene rgy return through litterfall was estimated as 12.648×10 6J·m -2 for the mixed fo rest, being 4 2% higher than that of the pure forest, and a large proportion of the energy return comprised leaf litter. The conversion efficiency of solar rad i ation energy into litterfall was 0 56% for mixed forest and 0 54% for pure for es t, respectively. The monthly energy flux in litterfall of Chinese fir showed a t hree-apex curve, peaked in March, August and December, respectively, which was s imilar to that in various fractions of leaf, twig, flower and fruit litter. The consistency in monthly patterns among different litter fractions of Chinese fir was attributed to their solid connections all the while. The monthly energy flux in litterfall of T. odorum culminated in January, May and August, the same was true for its leaf and twig litter. However, energy flux in flower litter only oc curred during March to May and that in fruit litter appeared in January and Marc h. The monthly dynamics of energy flux through litterfall of the two forests wer e both determined by their respective litterfall pattern of Chinese fir. Seasona l energy flux in litterfall for both mixed and pure forests followed the sequenc e of spring>winter>summer>autumn, but fluctuations in the former were less disti nct than those in the latter.

Effect of Mixed Forests of Chinese Fir and Tsoong's Tree on Soil Properties

An investigation and on 13 year old (1984～1996) Chinese fir and Tsoong's tree mixed forests in Jianou City, Fujian Province, China was carried out to compare the influences of different interplanting types of individual tree tree, row row, row strip (three rows) and pure Chinese fir stands on soil properties. Compared with the pure stands of Chinese fir, the mixed stands exerted a positive effect on soil fertility, with increases in soil organic matter, total N, available P and available K. Moreover, improvements were also observed in soil enzymatic activities, aggregate structure, structure stability, status of soil porosity, soil aeration and penetrability in mixed stands. The row row interplanted stands had the best effect on tree growth and soil properties among these mixed forests. In the southern subtropical region, the spreading of the row row mixing model of the two tree species would be helpful to preventing the soil from fertility deterioration caused by successive plantation of Chinese fir.

Effect of Slash Burning on Nutrient Removal and Soil Fertility in Chinese Fir and Evergreen Broadleaved Forests of Mid-Subtropical China

A Chinese fir forest (Cunninghamia lanceolata, CF) and an evergreen broadleaved forest (EB) located inFujian Province, southeastern China, were examined following slash burning to compare nutrient capital andtopsoil properties with pre-burn levels. After fire, nutrient (N, P and K) removal from burning residues wasestimated at 302.5 kg ha-1 in the CF and 644.8 kg ha-1 in the EB. Fire reduced the topsoil capitals of totalN and P by about 20% and 10%, respectively, in both forests, while K capital was increased in the topsoils ofboth forests following fire. Total site nutrient loss through surface erosion was 28.4 kg (N) ha-1, 8.4 kg (P)ha-1 and 328.7 kg (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 associatedwith 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 yearafter fire on the burned CF and EB topsoils. These results suggest that short-term site productivity canbe stimulated immediately, but reduced subsequently by soil and water losses, especially in South China,where high-intensity precipitation, steep slopes and fragile soil can be expected. Therefore, the silviculturalmeasurements should be developed in plantation management.

Soil C and N Pools in Chinese Fir and Evergreen Broadleaf Forests and their Changes with Slash Burning in Mid-Subtropical China

Soil organic carbon （C） and total nitrogen （N） pools of a Chinese fir （Cunninghamia lanceolata （Lamb.） Hook.） （CF） forest, and an evergreen broadleaf （EB） forest located in mid-subtropical, southeastern China, were compared before clearcutting, with the effect of slash burning on organic C and total N in the top 10 cm of soil before and after burning also being evaluated. Prior to clearcutting CF forest had significantly lower （P 〈0.05） organic C and total N in the soil （0-100 cm） compared to EB forest with approximately 60% of the C and N at the two forest sites stored at the 0 to 40 cm soil. In post-burn samples of the 0-10 cm depth at 5 days, 1 year, and 5 years for CF and EB forests, significantly lower levels （P 〈0.05） of organic C and total N than those in the pre-burn samples were observed. Compared to the pre-burn levels, at post-burn year 5, surface soil organic C storage was only 85% in CF forest and 72% in EB forest, while total N storage was 77% for CF forest and 73% for EB forest. Slash burning caused marked long-term changes in surface soil C and N in the two forest types.

Effect of temperature on soil respiration in a Chinese fir forest

Soil samples collected from the surface soil （0-10 cm） in an 88-year-old Chinese fir （Cunninghamia lanceolata） forest in Nanping Fujian, China were incubated for 90 days at the temperatures of 15℃, 25℃ and 35℃ in laboratory. The soil CO2 evolution rates were measured at the incubation time of 2, 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80 and 90 days. The results showed that CO2 evolution rates of soil samples varied significantly with incubation time and temperature during the incubation period. Mean CO2 evolution rate and cumulative amount of CO2 evolution from soil were highest at 35℃, followed by those at 25℃, and 15℃. Substantial differences in CO2 evolution rate were found in Q10 values calculated for the 2nd and 90th day of incubation. The Q10 value for the average CO2 evolution rate was 2.0 at the temperature range of 15-25℃, but it decreased to 1.2 at 25 35℃. Soil CO2 evolution rates decreased with the incubation time. The cumulative mineralized C at the end of incubation period （on the 90th day） was less than 10% of the initial C amounts prior to incubation.

Comparative study on active soil organic matter in Chinese fir plantation and native broad-leaved forest in subtropical China

Active soil organic matter (ASOM) has a main effect on biochemical cycles of soil nutrient elements such as N, P and S, and the quality and quantity of ASOM reflect soil primary productivity. The changes of ASOM fractions and soil nutrients in the first rotation site and the second rotation site of Chinese fir plantation and the native broad-leaved forest were investigated and analyzed by soil sampling at the Huitong Experimental Station of Forestry Ecology (at latitude 26°48′N and longitude 109°30′E under a subtropical climate conditions), Chinese Academy of Sciences in March, 2004. The results showed that values of ASOM fractions for the Chinese fir plantations were lower than those for the broad-leaved forest. The contents of easily oxidisable carbon (EOC), microbial biomass carbon (MBC), water soluble carbohydrate (WSC) and water-soluble organic carbon (WSOC) for the first rotation of Chinese fir plantation were 35.9%, 13.7%, 87.8% and 50.9% higher than those for the second rotation of Chinese fir plantation, and were 15.8%, 47.3%, 38.1% and 30.2% separately lower than those for the broad-leaved forest. For the three investigated forest sites, the contents of MBC and WSOC had a larger decrease, followed by WSC, and the change of EOC was least. Moreover, soil physico-chemistry properties such as soil nutrients in Chinese fir plantation were lower than those in broad-leaved forest. It suggested that soil fertility declined after Chinese fir plantation replaced native broad-leaved forest through continuous artificial plantation.

THE COMBUSTIBILITY OF CHINESE FIR AND MACCLURE MICHELIA MIXED FOREST

Based on the theory of forest burning link, the combustibility of the 6-year-old Chinese fir (Cunninghamia lanceolata) and macclure michelia (Michelia macclurei) mixed forest was determined in Youxi County, Fujian Province from 1988 to 1989. The results show that the daily mean moisture in the forest, moisture content of litter and the water reserves of the stand in mixed forest are 3%, 7.6% and 46.8% higher than that in pure stand respectively, the inflammables quantity and energy ratios of the stand biomass and total potential energy in mixed stand are 8.5% and 3.69% lower than that in pure stand respectively. Mixed forest can decrease the combustibility of stand.

Stability of soil organic carbon changes in successive rotations of Chinese fir(Cunninghamia lanceolata(Lamb.) Hook) plantations

The importance of soil organic carbon （SOC） under forests in the global carbon cycle depends on the stability of the soil carbon and its availability to soil microbial biomass. We investigated the effects of successive rotations of Chinese fir （Cunninghamia lanceolata （Lamb.） Hook） plantations on the stability of SOC and its availability to microbes by adopting the two-step hydrolysis with H2SO4 and density fractionation. The results showed that successive rotations of Chinese fir decreased the quantity of total SOC, recalcitrant fraction, and carbohydrates in Labile Pool I （LPI）, and microbial properties evidently, especially at 0-10 cm horizon. However, cellulose included in Labile Pool Ⅱ （LP Ⅱ） and the cellulose/total carbohydrates ratio increased in successive rotations of Chinese fir. The noncellulose of carbohydrates included in LPI maybe highly available to soil microbial biomass. Hence the availability of SOC to microbial biomass declined over the successive rotations. Although there was no significant change in recalcitrance of SOC over the successive rotations of Chinese fir, the percentage of heavy fraction to total SOC increased, suggesting that the degree of physical protection for SOC increased and SOC became more stable over the successive rotations. The degradation of SOC quality in successive rotation soils may be attributed to worse environmental conditions resulted from disturbance that related to ＂slash and burn＂ site preparation. Being highly correlated with soil microbial properties, the cellulose/total carbohydrates ratio as an effective indicator of changes in availability of SOC to microbial biomass brought by management practices in forest soils.

毛竹扩张对幕阜山区森林土壤碳氮磷含量及生态化学计量特征的影响

以幕阜山区同一片毛竹林向两侧杉木林和阔叶林扩张形成的连续生态界面为研究对象,分析不同林型土壤有机碳(SOC)、全氮(TN)、全磷(TP)、硝态氮(NO_(3)^(−)−N)、铵态氮(NH_(4)^(+)−N)含量及其生态化学计量比,探讨毛竹不同扩张模式对森林土壤碳(C)、氮(N)、磷(P)的影响。结果表明:在2种扩张模式下,随土壤层次的增加,除NO_(3)^(−)−N呈不规律变化外,SOC、TN、TP、NH_(4)^(+)−N含量均呈逐渐降低趋势。在毛竹向杉木林扩张过程中,杉木林、竹杉混交林、毛竹林同一土层SOC、TN、TP含量均无显著差异;在毛竹向阔叶林扩张过程中,毛竹林0~10 cm土层SOC和TN含量较阔叶林和竹阔混交林分别降低了27.71%、30.45%和36.67%、31.11%,而在10~20 cm和20~30 cm土层则无显著差异;毛竹扩张对杉木林和阔叶林各土层TP含量无显著影响;毛竹向杉木林扩张增加了0~10 cm和20~30 cm土层NH_(4)^(+)−N含量,毛竹向阔叶林扩张增加了10~20 cm土层NH_(4)^(+)−N含量及20~30 cm土层NO_(3)^(−)−N含量;毛竹向杉木林扩张对土壤C/N、C/P、N/P无显著影响,毛竹向阔叶林扩张导致0~10 cm土层N/P明显降低、10~20 cm土层C/N显著增加。综上,毛竹向杉木林扩张对土壤SOC、TN、TP影响不显著,但提升了表层和深层土壤NH_(4)^(+)−N含量,毛竹向阔叶林扩张造成表层土壤SOC、TN含量显著降低,并导致中层土壤NH_(4)^(+)−N含量和深层土壤NO_(3)^(−)−N含量明显增加。

Composition and properties of soil humus in a mixed forest of Cunninghamia lanceolata and Tsoongiodendron odorum

This study was conducted in Xinkou Experimental Forestry Farm of Fujian Agricultural and Forestry University, Sanming, Fujian Province in January 1999. Taking pure stand of Chinese fir as control, the authors measured and studied the content of organic carbon, content of humic acid (HA), ratio of HA to fulvic acid (FA), and the characteristics of infrared light spectrum and visible light spectrum of soil humus in the mixed forest of Chinese fir and Tsoong?tree. Compared to humus composition in the pure stand of Chinese fir, the content of soil organic C, HA content, and the E4 value of HA for different layers of soil, except for the ratio of HA to FA, showed a significant increase in the mixed forest, while the ratios of E4 to E6 had a little decrease. The infrared light spectrum of humic acid had an absorptive peak at 1650 cm-1. It is concluded that the levels of humification and aromaticity of soil humus are higher in the mixed forest, which is favorable for the improvement of soil structure and nutrient supply, thus improving the soil fertility to a certain degree.

杉木林分密度对套种闽楠树型、光合能力及生物量分配的影响

[目的]通过探讨不同林分密度杉木林下套种闽楠的树型结构、光合作用及生物量分配的适应性变化规律,为杉木近成熟林林分质量精准改造与提升提供科学依据。[方法]选择21年生杉木人工林为研究对象,通过设置375株·hm^(-2)、570株·hm^(-2)、630株·hm^(-2)和810株·hm^(-2)等4个间伐保留密度处理,分别进行林下套种900株·hm^(-2)闽楠形成杉阔复层林,测定分析林下套种5 a后闽楠冠型、侧枝长度、分枝角、叶片形态、叶绿素荧光参数、SPAD值,以及侧枝、茎干和叶片不同器官生物量等主要适应性生长指标的差异,探讨林分密度对林下套种闽楠树冠形态特性、光合能力及生物量分配的影响规律。[结果]低林分密度(375株·hm^(-2)和570株·hm^(-2))杉木下套种的闽楠2级侧枝长、1级和2级侧枝密度大于810株·hm^(-2)林分密度处理。闽楠叶片的叶面积、比叶面积表现出随着杉木林分密度增加而增加,其中,杉木林分密度375株·hm^(-2)的叶面积、比叶面积显著小于杉木林分密度810株·hm^(-2),相差80.97 cm^(2)和10.43 cm^(2)·g-1;810株·hm^(-2)林分密度处理下,闽楠叶片的叶绿素荧光参数和SPAD值均高于375株·hm^(-2)林分密度处理。低林分密度下(375株·hm^(-2)和570株·hm^(-2))套种的闽楠下层树冠叶片、总叶片生物量、以及侧枝和茎干生物量均显著大于810株·hm^(-2)林分密度处理(p<0.05)。375株·hm^(-2)林分密度处理下,闽楠通过增加株高,促进侧枝生物量积累;810株·hm^(-2)林分密度处理下,闽楠减少对株高的投资,从而增加叶片生物量的积累。[结论]在低林分密度(375株·hm^(-2)和570株·hm^(-2))下,林下光照充足有利于闽楠生物量积累,侧枝生长,其生长状况较好;在高林分密度下(630株·hm^(-2)和810株·hm^(-2)),闽楠可通过促使叶片长度变长,增大叶片比叶面积,增加叶片SPAD值,提高光合电子传递速率和光能捕获效率等变化来增强光捕获能力,从而适应光照资源不足的生存环境。

武夷山杉木林丛枝菌根真菌沿海拔的变化特征及其影响因素

丛枝菌根共生体是丛枝菌根真菌(Arbuscular Mycorrhizal Fungi,AMF)与宿主植物之间形成的互惠共生形式。共生体中的碳、氮、磷交换和代谢影响着宿主植物和共生真菌之间的营养平衡和资源重新分配,对陆地生态系统植物体的生长发育具有重要作用。本研究以武夷山3个海拔(1400 m,800 m,200 m)杉木人工林为研究对象,分析了不同海拔杉木林根际土壤、杉木特征指标之间的总体差异,以及海拔梯度中主导AMF变化的环境影响因素。结果表明:土壤有机碳、可溶性有机碳、微生物生物量碳含量均随海拔的升高而显著增加;不同海拔杉木林中,AMF特征指标除侵染率不变外,孢子、球囊霉素和菌丝密度均随海拔呈上升趋势。综合主成分分析第一和第二主成分各因子贡献值表明,土壤有机碳、温度、含水率、可溶性有机碳、总氮以及微生物生物量碳是影响AMF变化的重要因素;冗余分析结果进一步表明,可溶性有机碳对AMF影响最大,说明海拔梯度上易利用底物可能是影响杉木AMF特征变化的关键因子。研究结果对于了解和预测AMF如何调控亚热带杉木林生态系统功能及其对气候变化的响应具有重要意义。

杉木林下植物多样性对不同间伐年限的响应

探究间伐对杉木林下植物多样性的动态影响,可为杉木林可持续经营和生态效益评价提供依据。以浙西南杉木林为对象,采用空间代替时间的方法,对间伐1、3、8 a后和未间伐(0 a)的林下植物种类、重要值及多样性进行全面调查与分析。结果表明:间伐0、1、3、8 a后杉木林下植物种类分别有37、48、59、66种,其中不同间伐年限杉木林下共有的植物35种。随着间伐年限的延长,杉木林下植物种类增加速度表现为“先快后慢”的趋势,与0 a相比,间伐1、3、8 a后林下灌木、草本和藤本植物种类分别增加了38.5%~100.0%、27.8%~72.2%、16.7%~66.7%。杉木林下排名前3的灌木、草本和藤本植物的优势种重要值之和随着间伐年限的增加总体呈现降低趋势。未间伐杉木林下没有阳性植物生长,间伐后种类增加到12~13种;中性植物种类随着间伐年限的延长而增加,与0 a相比,间伐3、8 a后分别增加了50.0%和85.0%。杉木林下植物的多样性指数随着间伐年限的延长而增大,灌木、草本植物的优势度指数Simpson、多样性指Shannon-Wiener和丰富度指数Margalef在不同间伐年限间的差异达显著水平(P<0.05),藤本植物的Simpson、Shannon-Wiener和Margalef表现为间伐3、8 a后显著高于0 a(P<0.05),植物的均匀度指数Pielou在不同间伐年限间没有显著性差异(P>0.05)。

间伐对杉木林枯落物和土壤水源涵养能力的动态变化分析

探讨不同间伐年限对杉木林枯落物层和土壤层持水能力的影响,为评估杉木林水源涵养功能对间伐的响应提供科学依据。以浙西南景宁县间伐1年、间伐3年、间伐8年和未间伐的杉木林为对象,采集枯落物与土壤样品,分析测定枯落物含水率、持水能力、土壤容重、非毛孔隙度并计算相关指标。结果表明:杉木林枯落物现存量在不同间伐年限间的差异并不显著(P>0.05);枯落物持水量、持水速率与浸水时间的关系分别符合对数函数和幂函数;间伐8年的杉木林枯落物层的最大持水率、最大拦蓄率和有效拦蓄率均显著高于未间伐林分(P<0.05);间伐3年、间伐8年的杉木林枯落物最大持水量和有效拦蓄量均显著高于未间伐林分;间伐8年杉木林地0~10 cm土层土壤容重显著降低(P<0.05),非毛管孔隙度显著增大,非毛管持水量显著增加了22.4%(P<0.05),而对10~30 cm土层土壤储水性能相关指标的影响不显著(P>0.05)。综上,杉木林枯落物层和土壤层的水源涵养功能随着间伐年限的延长而增强。

Dynamics of nitrogen and phosphorus concentrations of fine roots in a mixed forest of Cunninghamia lanceolata and Tsoongiodendron odorum

From September 1999 to July 2000, N and P concentrations of fine roots were measured with the method of sequential soil core at bimonthly intervals in a mixed forest of Tsoong's tree (Tsoongiodendron odorum Chun) and Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) in Sanming, Fujian. The results showed that N, P concentration of Chinese fir and Tsoong's tree in fine roots were negatively related to root diameter size. The concentrations of N and P in living roots and dead roots were compared. The order of N concentration in fine roots in different samples was Tsoong's tree>undergrowth>Chinese fir, while that of P was undergrowth>Tsoong's tree>Chinese fir. For Chinese fir, the seasonal change of N, P concentrations in fine roots with various diameter classes showed a single-apex curve with a maximum in September. For Tsoong's tree, maximized concentration of N in fine roots appeared in July or September and maximized P concentration in May.

杉木纯林套种阔叶树种后林分空间结构变化及综合评价

为了解杉木纯林林分空间结构变化,本文采用四株木法构建林分空间结构单元,基于福寿林场不同龄组的杉木纯林6个样地的实测数据,将定性与定量分析结合,选取角尺度、混交度、开敞度、大小比数和林层指数等5个林分空间结构指标对幼龄杉木纯林和中龄杉木纯林在套种阔叶树种前后的林分空间结构特征变化进行分析,采取乘除法对林分空间结构各个指标进行评价。根据计算出的林分空间结构评价指数,将林分空间结构划分为5个评价等级;等级越高,则表明林分空间结构越合理,林层越丰富。结果表明:(1)套种阔叶树种前,幼、中龄杉木纯林空间结构指标角尺度分别为0.3687、0.3464,混交度分别为0.1507、0.0627,开敞度分别为0.9778、0.4338,大小比数分别为0.4991、0.5225,林层指数分别为0.2495、0.3414。林分空间结构评价指数分布范围是0.1862~0.3876,1级样地数占样地总数的16%,2级样地数占样地总数的84%。(2)套种阔叶树种后,幼、中龄杉木纯林空间结构指标角尺度分别为0.3289、0.2197,混交度分别为0.3857、0.1629,开敞度分别为1.7182、0.7136,大小比数分别为0.4064、0.4377,林层指数分别为0.3063、0.5123。林分空间结构评价指数数值分布范围是0.5921~0.8573,4级、5级样地数各占样地总数的50%。研究结果可为杉木纯林套种阔叶树种这一林分空间结构优化经营措施的实践提供新的参考依据。

基于机载激光雷达技术的山区针叶林单木分割方法研究

以杉木为研究对象,利用无人机激光雷达点云数据,结合地面实测样地数据,探索创新现有的森林资源调查模式,提升森林资源外业调查效率,更新资源调查数据,保证数据的现势性。考虑到研究区为山地林区,地面起伏较大,选取了一种基于改进加密三角网滤波算法进行滤波和分类,并对比分析了分水岭、点云分割、层堆叠种子点三种不同的单木分割方法,完成了研究区单木位置、树高、冠幅等林木参数的提取研究,优化了激光雷达林木参数反演的技术流程。从30个样地中抽取10个样地,对比样木实测值与单木分割的估测值,结果表明:层堆叠种子点算法分割效果最优,F评分在64.61%~85.29%之间;点云分割算法居中,F评分在56.00%~80.60%之间;分水岭算法分割效果最差,F评分在45.57%~69.45%之间。同一种方法中,不同样地分割效果也存在差异,这可能与样地地形、树木结构形态等因素有关;样地中林木分布存在树木遮挡或树木分布结构不规则时,一定程度会降低单木分割精度。因此,根据不同林分情况,建立适用性较强的无人机激光雷达森林参数反演模型是未来努力的方向。

杉木近熟林间伐套种闽楠幼林生长状况研究

以福建省永安市24年生杉木近熟纯林为研究对象,通过对比杉木间伐后套种闽楠、不间伐套种闽楠及同步营造闽楠纯林3种模式,分析闽楠生长状况。结果表明:杉木遮荫有助于提高闽楠幼树成活率,6年后间伐套种闽楠的保存率最优,且其树高、胸径、材积均显著优于其他处理,包括纯林更新和不间伐套种。研究证实了杉木与闽楠异龄复层混交模式在促进两树种协同生长上的有效性,但随着闽楠密度增加和树龄增长,种间竞争加剧。此发现为杉木纯林改造及大径材与珍稀阔叶树培育提供了创新经营模式。

Changes in Soil Carbon Pools Induced by Substitution of Plantation for Native Forest

Changes in soil carbon pools under Chinese fir (Cunninghamia lanceolata) andbamboo (Phyllostachys pubescens) plantations substituted for a native forest (Quercus acutissima,Cyclobalanopsis glauca, Cas-tanopsis sclerophylla, Platycarya strobilacea, Lithocarpus glaber) werestudied on the hills with acid parent rock and soils classified as red soils (Ferrisols) in Huzhou,Zhejiang Province of east China. It was found that total soil organic carbon (TSOC), easilyoxidisable carbon (EOC) and water-soluble organic carbon (WSOC) under bamboo plantation wereincreased, but microbial biomass carbon (MBC) was decreased. On the contrary, Chinese fir induceddeclines of all fractions of C including TSOC, EOC, WSOC and MBC. The percentages of the activefractions of soil C (EOC and WSOC) were increased in the plantations as compared to the nativebroad-leaved forest, but proportions of soil organic C as MBC were decreased. It could be concludedthat bamboo plantation had a great ability of not only fixing C but also accelerating soil C poolcycle, improving nutrient and microorganism activity; therefore, it is a good ecosystem and could berecommended for wide development. Chinese fir would shrink the soil C pool and deteriorate soilbiological fertility, so it did not benefit CO2 fixing and land sustainable utilization.

Soil Biological Changes for a Natural Forest and Two Plantations in Subtropical China

Conversion of natural forests into pure plantation forests is a common management practice in subtropical China.To evaluate the effects of forest conversion on soil fertility, microbe numbers and enzyme activities in topsoils (0-10 cm)were quantified in two 33-year-old monoculture plantations of Castanopsis kawakamii Hayata (CK) and Cunninghamia lanceolata Lamb. (Chinese fir) (CF), and compared to a neighboring relict natural C. kawakamii forest (NF), in Sanming,Fujian. Five soil samples were collected once each in January, April, July, September and November in 2000 in each forest for laboratory analysis. Over the sampling year, there were significant differences for bacteria, fungi and actinomycetes between forests and between seasons (P ＜ 0.05). The largest bacteria and fungi populations were in NF, while CF contained the greatest number of actinomycetes. There were also significant differences (P ＜ 0.05) with microbial respiration for forests and seasons. Additionally, compared with NF, urease and acid phosphatase were significantly lower (P ＜ 0.05)in CK and CF. Also, the correlations of soil hydrolysable N and available P to soil microbial and enzymatic activities were highly significant (P ＜ 0.01). Thus, to alter the traditional Chinese fir monoculture so as to mimic the natural forest conditions, managing mixed stands of Chinese fir and broadleaf trees or conducting crop rotation of conifers and broadleaf trees as well as minimizing forest disturbances like clear-cutting, slash burning and soil preparing, could be utilized.