2006——2015英语四级作文题目及答案
历年大学英语四级作文及答案
哀牢山亚热带常绿阔叶林乔木碳储量及固碳增量*张鹏超1,4 张一平1,2,3** 杨国平1,2,3 郑 征1,2,3 刘玉洪1,2,3 谭正洪1,4(1中国科学院热带森林生态学重点实验室(西双版纳热带植物园),云南勐仑666303;2中国科学院哀牢山亚热带森林生态系统研究站,云南景东676209;3云南哀牢山森林生态系统国家野外科学观测研究站,云南景东676209;4中国科学院研究生院,北京100049)摘 要 为了解哀牢山亚热带常绿阔叶林的乔木碳储量及其固碳增量,利用2005和2008年的植被调查数据,对哀牢山3种主要常绿阔叶林的乔木碳储量及其固碳增量进行了分析㊂结果表明:原生的中山湿性常绿阔叶林㊁滇山杨次生林和旱冬瓜次生林的乔木碳储量分别为257.90㊁222.95和105.39t C ㊃hm -2;中山湿性常绿阔叶林乔木碳储量主要存储在DBH≥91cm 的乔木中(34.68%);而次生林的乔木碳储量主要分布在径级21cm≤DBH<41cm 的乔木中(滇山杨林77.29%;旱冬瓜林69.28%)㊂由此可见,哀牢山地区原生的中山湿性常绿阔叶林乔木层在碳蓄积方面占主导优势㊂哀牢山亚热带常绿阔叶林的3个森林类型乔木层均具有固碳增量,即使是原生的中山湿性常绿阔叶林,其乔木层年平均固碳增量也达2.47t C ㊃hm -2㊃a -1;次生林乔木层的年平均固碳增量约为原生林的2倍,显示了哀牢山亚热带常绿阔叶林乔木层具有较强的碳汇增量㊂初步估算,哀牢山亚热带常绿阔叶林林区内每年乔木固碳增量为8.52×104t C ㊃a -1㊂关键词 亚热带常绿阔叶林;生物量;碳储量;哀牢山*国家重点基础研究发展计划项目(2010CB833501)㊁中国科学院知识创新工程重要方向项目(KZCX2⁃YW⁃Q1⁃05⁃04)㊁国家自然科学基金项目(40571163)和国家重点基础研究发展计划资助项目(2003CB415101)㊂**通讯作者E⁃mail:yipingzh@收稿日期:2010⁃01⁃18 接受日期:2010⁃03⁃16中图分类号 S718.5,Q948.1 文献标识码 A 文章编号 1000-4890(2010)6-1047-07Carbon storage and sequestration of tree layer in subtropical evergreen broadleaf forests in Ailao Mountain of Yunnan.ZHANG Peng⁃chao 1,4,ZHANG Yi⁃ping 1,2,3,YANG Guo⁃ping 1,2,3,ZHENG Zheng 1,2,3,LIU Yu⁃hong 1,2,3,TAN Zheng⁃hong 1,4(1Key Laboratory of Tropi⁃cal Forest Ecology ,Xishuangbanna Tropical Botanical Garden ,Chinese Academy of Sciences ,Menglun 666303,Yunnan ,China ;2Ailaoshan Station for Subtropical Forest Ecosystem Studies ,Jingdong 676209,Yunnan ,China ;3National Forest Ecosystem Research Station at Ailaoshan ,Jingdong 676209,Yunnan ,China ;4Graduate University of Chinese Academy of Sciences ,Beijing 100049,China ).Chinese Journal of Ecology ,2010,29(6):1047-1053.Abstract :In order to understand the tree layer carbon storage and sequestration in the subtropi⁃cal evergreen broadleaf forests in Ailao Mountain,an analysis was made on the tree layer carbon storage and sequestration in three dominant forests in the Mountain,based on the field surveys in 2005and 2008.The tree layer carbon storage in the primary evergreen broadleaf forest,seconda⁃ry Populus bonatii forest,and secondary Alnus nepalensis forest in the Mountain was 257.90,222.95,and 105.39t C㊃hm -2,respectively.The tree layer carbon storage of the primary ever⁃green broadleaf forest was mainly contributed by the trees with DBH ≥91cm (34.68%),while that of the two secondary forests was mainly contributed by the trees with DBH from 21cm to 41cm (77.29%for P.bonatii secondary forest,and 69.28%for A.nepalensis secondary forest),suggesting that the tree layer of primary evergreen broadleaf forest played an important role in the carbon storage in Ailao Mountain.The tree layers of the three forests all had the capability of car⁃bon sequestration.The mean annual increment of tree layer carbon sequestration in primary ever⁃green broadleaf forest was 2.47t C㊃hm -2㊃a -1,and that in the two secondary forests was about生态学杂志Chinese Journal of Ecology 2010,29(6):1047-1053two times of the primary evergreen broadleaf forest,suggesting a great potential of carbon seques⁃tration in secondary forests.Based on the above⁃mentioned results,it was estimated that the mean annual increment of tree layer carbon sequestration within the Ailao Mountain National Na⁃ture Reserve was8.52×104t C㊃a-1.Key words:subtropical evergreen broadleaf forest;biomass;carbon storage;Ailao Mountain. 自工业革命以来,由于人类活动如化石燃料燃烧和土地利用变化的影响,大气中CO2㊁CH4等温室气体浓度的急剧上升,导致了全球气候变化(Vi⁃tousek,1994;Rind,1999)㊂IPCC于2007年2月发布了第四次评估报告,指出全球气候变暖和极端气候事件已经成为一个不争的事实,近百年(1906 2005年)全球地表平均温度上升了0.74℃±0.18℃(IPCC,2007)㊂陆地生态系统是人类赖以生存和持续发展的生命支持系统,是受人类活动影响最强烈的区域,是大气碳的主要汇(Schimel,1995;方精云等,2001,2007)㊂森林生态系统是地球生物圈的重要组成部分,储存了陆地生态系统中有机碳地上部分的80%,地下部分的40%(Malhi et al.,1999)㊂森林生态系统的碳储量不仅是研究森林生态系统与大气碳交换的基本参数(Dixon et al.,1994),也是估算森林生态系统与大气排放含碳气体的关键因子㊂由此可见,森林生态系统在全球碳循环与平衡中具有极为重要和不可替代的地位和作用㊂为了正确评价我国森林碳库在全球碳循环和碳平衡中的地位,我国学者围绕森林生态系统的碳储量㊁碳密度和碳汇功能做了大量的研究工作,取得了显著的成就(Fang et al.,2001;方精云和陈安平, 2001;于贵瑞,2003;胡会峰和刘国华,2006)㊂从生物生产与气候关系的角度,碳蓄积主要发生在热带和亚热带(Watson et al.,2000)㊂亚热带由于面积广大㊁气候类型和地貌单元多样,森林生态系统的类型变化大,而且复杂㊂在我国的亚热带,除西部外,其他地区均为人口稠密区,对森林资源的开发和破坏都非常大㊂目前大部分森林的林龄不大,且人工林占有相当比例,天然原始林所存非常有限㊂有关森林生态系统生物量和生产力的研究,以人工林最多,不但包括许多针叶林,如杉木林和马尾松林,而且包括阔叶林和针阔混交林,天然林的研究报道相对较少,且以天然次生林研究为主,难得有原始林的测定,即使是原始森林,也或多或少受到了人为干扰的影响(冯宗炜等,1999)㊂而哀牢山的上部分布着目前我国面积最大㊁保存最完整的亚热带山地湿性常绿阔叶林(吴征镒,1983)㊂不少学者对其群落类型和结构㊁树种多样性㊁生物量等方面进行了研究(邱学忠和谢寿昌,1998),但对该地区森林碳循环和碳储量的研究仍然十分薄弱㊂本研究以位于哀牢山国家级自然保护区内的哀牢山亚热带森林生态系统研究站(简称哀牢山生态站)的4块亚热带常绿阔叶林长期观测样地,即:中山湿性常绿阔叶林长期观测样地㊁中山湿性常绿阔叶林土壤生物采样地㊁滇山杨次生林辅助长期观测采样地和旱冬瓜次生林辅助长期观测采样地为对象,采用植被调查法,对哀牢山亚热带常绿阔叶林乔木碳储量及其固碳增量进行了分析㊂旨在探讨我国保存最为完好㊁面积最大的亚热带常绿阔叶林的乔木碳储量及其固碳增量的差异,为区域森林碳储量及其固碳潜力的估算提供科学依据,同时为将来在本地区开展碳循环研究提供数据支持㊂1 研究概况与研究方法1.1 自然概况哀牢山位于云南高原西南部㊁横断山区南段,绵延500余km,降雨充沛,其山体的上部分布着目前我国面积最大㊁保存最完整的亚热带山地湿性常绿阔叶林(吴征镒,1983),其面积约有34483hm2㊂研究地点位于哀牢山国家级自然保护区内的哀牢山生态站附近,地理位置为24°32′N,101°01′E,海拔2450m㊂其年平均气温为11.0℃,降水量1879.5 mm,蒸发量为1174.0mm,雨季相对湿度在90%以上㊂哀牢山生态站所在地区的主要森林类型包括亚热带中山湿性常绿阔叶林㊁滇山杨林㊁旱冬瓜林等㊂其中大面积分布的是原始的中山湿性常绿阔叶林,树龄在120年以上(邱学忠和谢寿昌,1998),主要以变色椎(Castanopsis rufescens)㊁木果柯(Lithocarpus xylocarpus)和硬壳柯(L.hancei)为优势种,林冠郁闭度高,植被盖度在0.85以上,群落高度为20~25 m,乔㊁灌㊁草垂直分层明显(吴征镒,1983),为成过熟林(谢寿昌等,1996)㊂8401 生态学杂志 第29卷 第6期 旱冬瓜林位于哀牢山生态站西北角,面积约98 hm2,是亚热带中山湿性常绿阔叶林遭受彻底破坏又加以火烧后逐渐形成的次生林㊂群落郁闭度为75%,群落高度为15m;群落优势种为旱冬瓜(Alnus nepalensis)㊂群落分层结构状况:乔木层,高15m,以旱冬瓜为主;灌木层以吴茱萸(Evodia rutaecarpa)为主,高1~3m;草本层,高在0.30m以下,紫茎泽兰(Ageratina adenophora)最多,层间附(寄)生植物较少,为中龄林㊂滇山杨林是亚热带中山湿性常绿阔叶林遭受到破坏后(如砍伐㊁火烧)所形成的次生林,也是本区域森林植物群落演替的先锋树种㊂研究区内主要出现在哀牢山生态站周围海拔2500m以下的低丘和缓坡地带,呈零星小片分布㊂调查样地的群落郁闭度为80%,高度为15~20m;优势种为滇山杨(Pop⁃ulus rotundifolia var.bonatii)㊁硬壳柯等㊂群落分层结构状况:乔木上层,高15~20m,乔木层以滇山杨为主,并伴生有硬壳柯㊁顺宁厚叶柯(Lithocarpus pachyphyllus var.fruticosus)等;灌木层以无量山箭竹为主,高1~3m;草本层,高在0.20m以下,以长穗兔儿风㊁沿阶草(Ophiopogon bodinieri)为常见,层间附生植物丰富,为中龄林㊂1.2 研究方法1.2.1 试验设置 在2008年按照中国生态研究网络(CERN)的规范,采用了植被调查方法,对代表哀牢山地区亚热带常绿阔叶林的3种主要森林类型的4个样地:中山湿性常绿阔叶林(长期观测样地㊁土壤生物采样地)㊁滇山杨次生林辅助长期观测采样地和旱冬瓜次生林辅助长期观测采样地的全部挂牌乔木进行了调查,调查的项目主要是胸径≥2cm乔木的物种㊁胸径(1.3m处)㊁树高和冠幅㊂1.2.2 数据及计算方法 2005年的数据为哀牢山生态站定期植被调查数据,2008年数据为本研究的植被调查数据㊂进行统计分析时将2个中山湿性常绿阔叶林样地的调查数据进行了合并㊂利用植被调查数据,使用式(1),计算得出哀牢山亚热带常绿阔叶林林区3种主要森林类型中山湿性常绿阔叶林㊁滇山杨次生林和旱冬瓜次生林每棵树的生物量,再将每块样地中所有树的生物量相加就得到各森林类型乔木层的总生物量,最后根据式(2)由生物量计算出各森林类型乔木层的总碳储量㊂生物量计算方法:W=aD b(1)式中:W为乔木总生物量,D为胸径,a㊁b为方程中的经验参数㊂公式(1)根据哀牢山地区已有的生物量模型(邱学忠等,1984),进行了相应的转化,得出式中的a为0.1586,b为2.3591㊂碳储量计算方法:本研究中森林乔木层碳储量(W c)为森林乔木层生物量(W)乘以转换系数得到,本文采用目前国际上常用的转换系数0.5(即每g干物质的碳含量) (Lugo&Brown,1992;刘国华等,2000;Fang et al., 2001)㊂W c=0.5W(2)年平均固碳增量计算方法ΔW c=(W c2008-W c2005)/(2008-2005)(3)碳储量的平均年增长率计算方法Δ=(W c2008/W c2005)1/(2008-2005)-1(4)式(2) (4)中:W c为森林乔木层碳储量,ΔW c为森林乔木层的年平均固碳增量,Δ为森林乔木层碳储量的年平均增长率㊂本研究计算的森林植被碳储量为乔木层碳储量,未包括林下层㊁灌木㊁草本及凋落物碳储量㊂2 结果与分析2.1 各森林类型乔木层的碳储量图1显示了哀牢山亚热带常绿阔叶林区各森林类型的乔木碳储量,2005年哀牢山中山湿性常绿阔叶林㊁滇山杨次生林和旱冬瓜次生林乔木层的碳储量分别为250.48㊁209.82和92.35t C㊃hm-2㊂2008年代表森林类型乔木层的碳储量分别为257.90㊁图1 2005年和2008年不同森林类型碳储量的比较Fig.1 Carbon storage between2005and2008in each for⁃est type9401张鹏超等:哀牢山亚热带常绿阔叶林乔木碳储量及固碳增量222.95和105.39t C㊃hm-2㊂可以看出,乔木层碳储量的大小关系为:中山湿性常绿阔叶林>滇山杨次生林>旱冬瓜次生林㊂由此可以认为,在云南中部亚热带常绿阔叶林森林林区,乔木层固碳能力最大的是中山湿性常绿阔叶林,其次是滇山杨次生林,最小的是旱冬瓜次生林㊂2.2 主要树种的碳储量哀牢山亚热带常绿阔叶林区不同森林类型乔木层中主要树种碳储量见表1㊂在亚热带中山湿性常绿阔叶林乔木层中,碳储量最大的是变色锥,2005年为67.20t C㊃hm-2,2008年为68.39t C㊃hm-2;其次是木果柯,2005年为59.15t C㊃hm-2,2008年为61.03t C㊃hm-2;这2个树种的碳储量分别占整个中山湿性常绿阔叶林乔木层的50.44%(2005年)和50.18%(2008年);在滇山杨次生林乔木层中,碳储量最大的是滇山杨,2005年为94.06t C㊃hm-2,2008年为98.64t C㊃hm-2;其次是硬壳柯, 2005年为63.90t C㊃hm-2,2008年为67.70t C㊃hm-2;这2个树种的碳储量占整个滇山杨林乔木层的75.28%(2005年)和74.61%(2008年);在旱冬瓜林乔木层中,碳储量最大是旱冬瓜,2005年为91.28t C㊃hm-2,2008年为104.09t C㊃hm-2;旱冬瓜的碳储量占整个旱冬瓜林乔木层的98.84% (2005年)和98.76%(2008年)㊂2.3 各森林类型乔木层不同径级碳储量的比较利用2008年的观测资料分析了哀牢山亚热带常绿阔叶林区不同森林类型乔木层中主要树种不同径级的碳储量(图2),并计算了相应的碳储量百分比(图3)㊂可见,对于亚热带中山湿性常绿阔叶林乔木层,以最大径级(Ⅹ级,DBH≥91cm)碳储量最高,为89.45tC㊃hm-2,占森林乔木碳储量的34.68%㊂在图2 不同森林类型主要树种的各径级乔木的碳储量Fig.2 Carbon storage of different diameter class in each forest typeⅠ级2≤DBH<11cm;Ⅱ级11≤DBH<21cm;Ⅲ级21≤DBH<31cm;Ⅳ级31≤DBH<41cm;Ⅴ级41≤DBH<51cm;Ⅵ级51≤DBH<61 cm;Ⅶ级61≤DBH<71cm;Ⅷ级71≤DBH<81cm;Ⅸ级81≤DBH<91 cm;Ⅹ级91cm以上㊂下同㊂图3 不同森林类型主要树种各径级的碳储量占总碳储量的百分比Fig.3 Percentage of carbon storage of different diameter class in each forest type表1 哀牢山亚热带常绿阔叶林区不同森林类型主要树种碳储量的比较(t C㊃hm-2)Tab.1 Comparison of the main tree species in carbon storage in evergreen broadleaf forest of Ailao Mountain树种中山湿性常绿阔叶林2005年2008年滇山杨林2005年2008年旱冬瓜林2005年2008年变色锥Castanopsis wattii67.2068.394.254.90--红花木莲Manglietia insights6.957.13----黄心树Machilus bombycina22.5223.60----木果柯Lithocarpus xylocarpus59.1561.034.124.74--南洋木荷Schima noronhae35.8337.010.400.48--硬壳柯Lithocarpus hancei3.543.5763.9067.70--折柄茶Hartia sinensis4.895.001.581.79--滇山杨Populus bonatii--94.0698.64--旱冬瓜Alnus nepalensis----91.28104.09其他50.3852.1741.5244.691.071.30总计250.48257.90209.82222.9592.35105.39 0501 生态学杂志 第29卷 第6期 图4 不同森林类型乔木层碳储量的平均年增长率Fig.4 Average annual growth rate of carbon storage in each forest type次生的滇山杨林和旱冬瓜林乔木层中,碳储量最高值基本上出现在中部的Ⅲ和Ⅳ级(21cm<DBH≤41 cm),分别为172.32和73.01t C㊃hm-2,分别占对应森林乔木碳储量的77.29%和69.28%㊂2.4 各森林类型的乔木年平均固碳增量利用2005和2008年的数据,以及式(3),可以计算得出,哀牢山亚热带中山湿性常绿阔叶林㊁滇山杨次生林和旱冬瓜次生林的乔木年平均固碳增量,分别为2.47㊁4.38和4.35t C㊃hm-2㊃a-1㊂可见,哀牢山亚热带常绿阔叶林林区不同森林类型乔木层年均固碳增量均为正值,大小关系为:滇山杨次生林>旱冬瓜次生林>中山湿性常绿阔叶林,显示了亚热带森林具有较强的碳汇潜力㊂2.5 不同森林类型乔木层碳储量的平均年增长率利用2005和2008年的数据,以及式(4),可以计算得出,哀牢山中山湿性常绿阔叶林㊁滇山杨次生林和旱冬瓜次生林乔木层碳储量的平均年增长率分别为0.98%㊁2.04%和4.50%(图4)㊂哀牢山碳储量的平均年增长率大小关系为:旱冬瓜次生林>滇山杨次生林>中山湿性常绿阔叶林㊂3 讨 论云南中部是我国常绿阔叶林分布的重点地区之一,具有亚热带高原特色,而位于云南省中部的哀牢山的上部分布着目前我国面积最大㊁保存最完整的亚热带山地湿性常绿阔叶林(吴征镒,1983),所以本研究选取了地处云南中部的哀牢山国家级自然保护区核心地带的4块样地作为研究地,其结果可以认为是代表了云南中部地区㊂在原生的亚热带中山湿性常绿阔叶林中(表1),组成群落的主要种的变色锥和木果柯的碳储量占据整个乔木碳储量的50%以上;在次生的滇山杨林中,碳储量主要集中在滇山杨和硬壳柯,其碳储量可达整个滇山杨林乔木层的75%左右;在次生的旱冬瓜林乔木层中,由于接近于纯林,优势树种旱冬瓜的碳储量占据了绝对优势,可达98%以上㊂进一步比较2005和2008年的数据可以发现,优势树种的碳储量所在比率在原生的亚热带中山湿性常绿阔叶林和旱冬瓜次生林乔木层是增加的,在滇山杨次生林乔木层中变化较小,显示了优势树种碳储量对森林碳储量具有较大贡献㊂在原生的中山湿性常绿阔叶林乔木层中,乔木的最大碳储量(89.45t C㊃hm-2)的乔木径级主要集中Ⅹ级(DBH≥91cm)㊂而次生的滇山杨林和旱冬瓜林乔木层的最大碳储量的乔木径级主要集中在Ⅲ和Ⅳ级(21cm<DBH≤41cm),分别为172.32和73.01t C㊃hm-2㊂可以认为:在原生的中山湿性常绿阔叶林乔木层中碳储量主要分布于大径级的乔木之中,这些大树寿命比较长,可视为一种长期的碳库;而次生林乔木层的碳储量主要分布在中径级的乔木中,随着乔木的生长,其在将来的碳储存方面将发挥越来越大的作用,是潜在的碳库㊂哀牢山亚热带常绿阔叶林林区,原生的中山湿性常绿阔叶林乔木层的碳储量最大(表1),2008年为257.90t C㊃hm-2,略低于我国森林生态系统的平均单位面积碳储量(258.83t C㊃hm-2)(周玉荣等,2000),大于全国植被的平均碳储量57.07t C㊃hm-2(周玉荣等,2000)㊁41.32t C㊃hm-2(赵敏和周广胜,2004)㊁41.00t C㊃hm-2(方精云等,2007);旱冬瓜次生林的碳储量最小,2008年为105.39t C㊃hm-2,但也高于全国植被的平均碳储量(57.07t C㊃hm-2)(周玉荣等,2000)㊂可以认为:在云南中部亚热带常绿阔叶林区,大面积原生的中山湿性常绿阔叶林乔木层在森林固碳方面发挥了很大的作用,中山湿性常绿阔叶林乔木层是云南中部阔叶林林区乔木碳储量的主要贡献者㊂如假设其固碳能力地区变化不大,则可以粗略估计云南中部亚热带常绿阔叶林区2008年的乔木总固碳量可达8.93×106t C (258.83t C㊃hm-2×34483hm2),比2005年8.64×106t C(250.48t C㊃hm-2×34483hm2)增加了0.29×106t C㊂哀牢山亚热带常绿阔叶林林区不同森林类型乔木层年均固碳增量均为正值,显示了哀牢山亚热带1501张鹏超等:哀牢山亚热带常绿阔叶林乔木碳储量及固碳增量常绿阔叶林乔木层均有碳储量潜力,每年都在存储大量的碳;哀牢山亚热带常绿阔叶林林区不同森林类型乔木层中,乔木年平均固碳增量的大小关系为:滇山杨次生林(4.38t C㊃hm-2㊃a-1)>旱冬瓜次生林(4.35t C㊃hm-2㊃a-1)>中山湿性常绿阔叶林(2.47t C㊃hm-2㊃a-1)㊂次生林的滇山杨次生林和旱冬瓜次生林乔木层的乔木年平均固碳增量数值相当,是原生的中山湿性常绿阔叶林乔木层的2倍,显示了次生林乔木层具有较强的碳汇潜力㊂研究表明,成熟林无论是地上部分还是地下部分,均贮藏着巨大的生物量,老龄森林生态系统在一定区域或全球尺度上对碳估算均起着巨大的作用(Suchanek et al.,2004)㊂值得注意的是,作为云南中部亚热带常绿阔叶林主要林分的亚热带中山湿性常绿阔叶林,虽然已经是120多年的成熟林(邱学忠和谢寿昌,1998),其乔木层碳储量可达257.90 t C㊃hm-2(2008年),并且仍然具有较强的碳汇潜力,其乔木层年固碳增量可达2.47t C㊃hm-2㊃a-1,碳储量的平均年增长率为0.98%,低于我国森林的平均年增长率1.6%(吴庆标等,2008)㊂因此,可以认为,作为云南中部的亚热带常绿阔叶林主要林分的亚热带中山湿性常绿阔叶林,一方面具有较大的森林面积(34483hm2),加之仍然具有较强的不可忽视碳汇潜力(乔木层为2.47t C㊃hm-2㊃a-1),仍然可以为国家在减排时做出巨大贡献,在2005 2008年间,乔木层每年就新增加固碳量29×104t C㊂如假设其固碳增量的地域变化不大,则云南中部的亚热带常绿阔叶林林区乔木层的每年的固碳量可达2.47t C㊃hm-2㊃a-1×34483hm2 =8.52×104t C㊃a-1㊂作为次生林的滇山杨林和旱冬瓜林乔木层,同样具有较强的固碳能力(222.95和105.39t C㊃hm-2);其年均固碳增量更大(4.38和4.35t C㊃hm-2㊃a-1),充分显示了作为地方土著种在固碳方面的显著作用,因此在人工造林时应该予以关注㊂本研究的3种亚热带常绿阔叶林的森林类型中,虽然旱冬瓜次生林乔木层的碳储量最小,但其平均年增长率最大,为4.50%,显示了具有较强的固碳潜力㊂有研究表明,随着乔木年龄的增长,树木所能固碳量的年增长率随之迅速增加(Lugo&Brown, 1992)㊂由此可以认为,随着时间的变化,次生林将发挥越来越大的固碳潜力㊂本研究以哀牢山为基础,探讨了云南中部常绿阔叶林林区乔木的碳储量及其固碳增量,显示了云南中部亚热带常绿阔叶林乔木具有较高的碳储量和固碳潜力,如果进一步考虑灌木和草本植物,云南中部的亚热带常绿阔叶林的碳储量及其固碳增量将会更高,所以进一步保护好云南中部的亚热带常绿阔叶林,对于国家制定减排战略㊁应对国际碳谈判等具有重要的意义,并可为国家实施减排做出贡献㊂由此可以认为,云南中部所保存的大量常绿阔叶林,具有巨大的碳储量及固碳潜力,保存好现有的原生常绿阔叶林,以保护和维持森林碳储量;禁止乱砍乱伐,减少因为采伐导致的森林碳储量的减少和碳汇潜力降低㊂另外,本研究表明,滇山杨作为亚热带常绿阔叶林的乡土树种,其构成的森林类型,同样具有较高的碳储量,应该在进行人工造林和清洁能源机制(CDM)中,成为优先考虑的树种;而旱冬瓜则具有较大碳储量平均年增长率,显示了较强的固碳潜力,也可作为人工林种植的选择树种㊂4 结 论在云南中部亚热带常绿阔叶林中,大面积存在的原生林的中山湿性常绿阔叶林乔木层的碳储量最大,2008年达257.90t C㊃hm-2,滇山杨林乔木层为222.95t C㊃hm-2,旱冬瓜次生林乔木层的碳储量最小,为105.39t C㊃hm-2㊂在原生的中山湿性常绿阔叶林乔木层中,碳储量主要集中在Ⅹ级(DBH≥91cm),占总碳储量的34.68%;次生的滇山杨林和旱冬瓜林乔木层的碳储量主要集中在Ⅲ和Ⅳ级(21cm≤DBH<41cm),占乔木层总碳储量的百分比,滇山杨林为77.29%;旱冬瓜林为69.28%㊂云南中部亚热带常绿阔叶林林区不同森林类型乔木层均具有碳储量潜力,每年都能够不断地存储大量的碳㊂即使是原始的㊁具有120多年树龄的成熟林 亚热带中山湿性常绿阔叶林,乔木层年平均固碳增量也达2.47t C㊃hm-2㊃a-1,显示出较高的固碳潜力;而作为次生林的滇山杨林和旱冬瓜林,其乔木层年均固碳潜力则为亚热带中山湿性常绿阔叶林的2倍(4.38和4.35t C㊃hm-2㊃a-1),充分显示了作为地方土著种的树种在固碳方面具有显著作用,在人工造林时应该予以关注㊂云南中部亚热带中山湿性常绿阔叶林㊁滇山杨次生林和旱冬瓜次生林乔木层碳储量的平均年增长率分别为0.98%㊁2.04%和4.50%㊂2501 生态学杂志 第29卷 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Suchanek TH,Mooney HA,Franklin JF,et al.2004.Carbon dynamics of an old⁃growth forest.Ecosystems,7:421-426.Vitousek PM.1994.Beyond global warming:Ecology and global change.Ecology,75:1861-1876. Watson RT,Noble IR,Bolin B,et nd⁃use,Land⁃use Change,and Forestry.Cambridge:Cambridge Univer⁃sity Press.作者简介 张鹏超,男,1983年生,硕士研究生㊂研究方向为生态气候㊂E⁃mail:zhangpc@责任编辑 王 伟3501张鹏超等:哀牢山亚热带常绿阔叶林乔木碳储量及固碳增量。
历年CET4作文真题及范文
Spring Festival Gala on CCTV (2006年12月四级真题）1.许多人喜欢在除夕观看春节晚会.2.有些人提出取消春节晚会.3.我的看法.范文一：As regards the Spring Festival Gala there has been a heated discussion among the general public in our society. People who believe in its necessity argue that the Spring Festival Gala performed on CCTV on New Year's Eve presenting grand sight and sound has already been considered as an indispensable custom by many Chinese people.By contrast, others hold that the 4-hour show is gradually losing its appeal and should be cancelled. The past two decades has witnessed a steady decrease in the number of people watching the Spring Festival Gale from 900 million to 700 million. With the roaring development of economy, various mass media come out like bamboo shoots after spring rain, making it increasingly difficult to cater to all tastes.As far as I am concerned, I prefer the program to stay. Served as an occasion for families to get together, the Spring Festival Gala is a tradition and treasure of the Chinese people.范文二Some people are in favor of the program. Those who like it have their reasons. First, they think that the gala is of tradition to us. What's more, some feel that they can find nothing to do except watching this on the eve of the Lunar New Year. Besides, it is said that this is a good chance for a family to have a rest happily.But others do not agree. People who dislike it have their reasons. Firstly, they say that they can find something else to do. Moreover, they argue that the spring festival gala on CCTV should not have been the most powerful program in this day.There is some truth in both arguments. But it is likely to do more harm than good, if you maintain that it is the only thing to do at that night. Some more meaningful things can be found easily, such as parties, sharing views with families, etc.. There is little doubt that further attention will be paid on this issue.范文三：It has been a hot topic for a long time whether the CCTV Spring Festival Gala should be cancelled or not. Many people advocate that CCTV Spring Festival Gala offers a wonderful opportunity to celebrate this traditional festival, for the Chinese all over the world can share the same happiness and excitement brought by the TV program. In addition, many performances are very impressive, and some can even positively affect our life value.However, every coin has two sides. Some people hold that CCTV Spring Festival Gala should be cancelled. One of the most significant reasons may be that this form of celebration force people to spend the eve more passively. What’s more, a great proportion of the programs are not attractive enough.As to me, my favor goes to the former opinion, because spring CCTV Spring Festival Gala gives us another option to celebrate this important moment. But it is really essential to improve the quality of the programs. And I hope some better forms of celebration will be created in the near future.（175 words）范文四：The approach of the Chinese Lunar New Year poses a national issue concerning the necessity of holding the CCTV Spring Festival Gala. Its established status is being challenged by a growing number of people, especially by younger generations. It is increasingly difficult to cater for all tastes.Some individuals deem that it should be canceled or replaced by other programs. These young people focus their attention on other forms of celebration instead of immersing themselves in TV. Despite that, the majority of mid-aged people and senior citizens uphold the importance of the traditional performance. The most striking feature of this gala is its traditionally close link with ordinary people's lives. Most of people view this gala as an annual staple on the traditional Chinese Spring Festival Eve. They all have a restless night and glue their eyes on the television.I am not supportive of the view that the grand gala should be abandoned. Undoubtedly, it plays a vital role in the celebration of Chinese New Year. To increase its appeal and meet young adults' need, the upcoming performance should invite some big names including super stars from Hongkong and Taiwan. We are all eagerly anticipating this unforgettable evening show.（转自/department/Article_Show.asp?NewsID=692）Recreational activity (2008年6月)1、娱乐活动多种多样，2、娱乐好处危害，3、依自己来说谈谈感受范文一：Recently, various recreational activities, such as dancing, internet games, running, have caused people’s atte ntion. However, the effects about them are divided on this point.Some people claim that the recreational activities are unquestionably beneficial to our daily life. In their eyes, recreational activities can help us to be healthier as well as help us to make more friends. On the contrary, some others consider the recreational activities can also do much harm. Some students are indulged in Internet games, which can hinder their normal studies.As for us, the college students, we should do sports regularly to make us stronger and healthier. At the meanwhile, it is also a “must” for us to fight against such recreational activities as the Internet games. Only with the efforts from all the college students, can the recreational activities bring us positive effects to our future development.范文二：In people's daily life, there are various recreational activities apart from studying or working ranging from Karaoke or dancing to computer games or sports games.Such activities are beneficial as well as harmful to us if undertaken inappropriately. On one hand, recreational activities can help us to not only build our body and mind but also improve our communication and understanding with friends because most of these activities are done with others. On the other hand, if we spend too much time on singing, dancing or other games, we might fail to concentrate on our duties such as studying our working, which in turn may lead to further consequences.As far as I'm concerned, recreational activities should be done within a certain limit so thatwe can keep a proper balance between recreation and studying or working life.Limiting the Use of Disposable Plastic Bags(2008年12月)1.一次性塑料袋曾被广泛的使用2.造成的问题3.限制使用的意义范文一：Disposable plastic bags were once widely used in China. When we went shopping at supermarkets and departments stores, shopping assistants often provided free plastic bags for our convenience. For a while, life without them seemed unimaginable for most of us.However, disposable plastic bags do bring severe damage to our environment. Costumers usually threw them away after use, and because they are thin and hard to decompose, these plastic products will exist for a long time. This is an immediate threat to our earth and water.Nowadays, the government has passed relevant regulations for limiting the use of disposable plastic bags: they are not free any more. In some shopping places, in order to invoke the public awareness of environmental protection, plastic bags are offered in a much higher price. As a result, people are changing their behavior: paper and clothing bags that vanished for a long time come back to our daily life. It is true that by limiting its usage, everyone in this society contributes some effort to the improvement of the environment.本文选自新东方周雷老师的博客：/zhouleiCreating a Green Campus（2009年12月）北京新东方学校王江涛1. 绿色校园的重要性，2. 什么样的校园是绿色的？3. 我们应该怎么做。
历年英语四级(CET4)考试作文题目
2015年6月英语四级作文题目【作文(一)：家长角色】【作文(二)：手机与教育】【作文(三)：现代生活】2014年12月英语四级作文真题及范文【作文(一)：印象最深活动】a campus activity that has benefited you most. state the reasons at least 120 No more than180 words【作文(二)：印象最深课程】A course that has impressed you most in college.【作文(三)：印象最深同学】The Most Impressive Classmate in My College2014年6月英语四级作文题目：【作文(一)】关于家乡Suppose a foreign friend of yours is coming to visit your hometown, what is the place would you show him or her and why.【作文(二)】关于中国Suppose a foreign friend of yours is coming to visit your China, what is the place would you show him or her and why.【作文(三)】关于校园Suppose a foreign friend of yours is coming to visit your campus, what is the place would you show him or her and why.2013年12月英语四级作文真题及范文【作文(一)】【作文(二)】People are crossing the street looking at their cell phones and using sticks in order to see.【作文(三)】漫画对白：Once I learn how to use google, isn't that all the education I really need?2013年6月英语四级作文真题及范文【作文(一)】图画作文：一屋不扫何以扫天下We cansee clearly from the cartoon there is a father talking with her son. Havingheard his son’s words that “ Dad, I am a bit worried about disposing of nuclearweapon.” The father replies that “ If you can empty the dustbin here, you cando anything”.【作文(二)】图画作文：大学生在校从商,创业,好不好?是学业重要,还是社会经历重要?For this part,you are allowed 30minutes to write a short essay.You should start your essay with a brief description of the picture and then express your views on the importance of learning basic skills.You should write at least 120 words but no more than 180 words.【作文(三)】图画作文：The Importance of Reading Literature2012年12月英语四级作文真题及范文【第一套试卷：】Directions: For this part, you are allowed 30 minutes to write A Letter Applying for a Bank Loan. You should write at least 120 words following the outline given below in Chinese.1. 你的基本情况your basic information12.你申请贷款的原因、数额及用途you reason for the loan, the amount and purpose3. 你如何保证专款专用以及你的还款打算【第二套试卷：】图表说明：全英文，无中文翻译和提示Education Pays, published every three years, presents detailed evidence of the private and public benefits of higher education. It also sheds light on the distribution of these benefits by examining both the increases and the persistent disparities in college participation and completion. In the three years between the publication of Education Pays 2007 and Education Pays 2010, median earnings for four-year college graduates increased more rapidly than those of high school graduates and the gap between the unemployment rates of the two groups grew. In addition to earnings comparisons, the report documents differences in lifestyles, health, and other outcomes for people with and without college education. Differences in enrollment and completion patterns across demographic groups highlight the reality that gaps in educational attainment are explained by a combination of money and other factors.2012年6月英语四级作文真题及范文Part Ⅰ Writing (30minutes)Directions: For this part, you are allowed 30 minutes to write a short essay entitled Excessive Packaging following the outline given below. You should write at least 120 words but no more than 180 words.1.目前许多商品存在过度包装的现象2.出现这一现象的原因3.我对这一现象的看法和建议2011年12月英语四级作文题目Directions: You're allowed 30 minutes to write a short essay entitled Nothing Succeeds Without a Strong Will by commenting on the humorous saying, "Quitting smoking is the easiest thing in the world. I've done it hundreds of time."You'd write at least 120 words but no more than 180 words.2011年6月大学英语四级真题Directions: For this part, you are allowed 30 minutes to write a short essay on the topic of Online Shopping. You should write at least 120 words following the outline given below:1.现在网上购物已成为一种时尚2.网上购物有很多好处，但也有不少问题3.我的建议Online Shopping2010年12月大学英语四级考试真题及答案详解Directions：For this part, you are allowed 30 minutes to write a short essay entitled How Should Parents Help Children to Be Independent? You should write at least 120 words following the outline given below.1. 目前不少父母为孩子包办一切2. 为了让孩子独立, 父母应该……How Should Parents Help Children to Be Independent?2010年6月英语四级考试真题Directions: For this part, you are allowed 30 minutes to write a short essay on the topic of Due Attention Should Be Given To Spelling. You should write at least 120 words following the outline given below:1. 如今不少学生在英语学习中不重视拼写2. 出现这种情况的原因3. 为了改变这种状况，我认为…Due Attention Should Be Given To Spelling。
2006~2013年英语四级作文真题及范文
2006~2013年英语四级作文真题及范文2013年6月英语四级作文真题三篇及范文详解：真题解析一：On Doing Small ThingsOn Doing Small Things图画的内容和构图不难：父亲和男孩子的对话，孩子说“ Dad，I am a bit worried about disposing of nuclear weapon. (爸爸，我有点担心清除核步器这个问题)”父亲则回答“ If you can empty the dustbin, you can do anythi ng. (如果你能把垃圾桶倒掉，你就能做好任何事情)” ，说话间，手指着垃圾桶。
作文的第一段，要进行简单描绘图画内容，这是必须的，也是题目中强制要求的(a brief description of the picture)。
描述的时候，只要把父子两的对话移植到第一段，然后把父亲手指垃圾桶的动作描绘一下就可以了，非常简单。
作文的第二段，进行主旨提炼并且论述。
这幅图画很容易看出主题，那就是做大事之前，要先做小事(一屋不扫，何以扫天下)，而且题目中其实早就已经透露了主题了(express your views on the importance of doing small things beforeundertaking something big)。
因此，第二段通篇论述小事做起的重要性就可以了。
属于作文三大分类之“积极主题，论述意义”。
作文第三段，总结，启发。
这一段再次强调小事做起的意义，我们不能低估它的威力。
文章最后可以以名人名言作为结尾。
请看范文We can see from the cartoon that there is a father talking with his son. Having heard his son‟s words that “Dad, I am a bit worried about disposing of nuclear waste。
近5年英语四级作文题目及范文
作文题目：Online Shopping1、现在网上购物已成为一种时尚2、网上购物有很多好处，但也有不少问题3、我的建议作文范文：Several decades ago, it should be a marvelous wonder to purchaseour favorite gifts only by clicking the mouse and then just waitingfor the door knock by a smiling expressive delivery courier withthe exact package you ordered. While, today, it is no long a rarecase. Combined with the fast food, the digital communication ,online shopping has been a common part of our life。
Admittedly, on line shopping offers magical convenience. Forexample, it saves time and offers numerous choices since floods ofinformation can be supplied on Internet. While, every coin has towsides and online shopping is no different. Have you stillremembered the annoying time when you found the commodities you buyon Internet was not the slightest(微博) as what you had expected and longtime had to be taken for its replace and even compensation.Actually, just with the seemingly beautiful pictures of theproducts on Internet, it is hard for us to make rational choices.After all, seeing is believing。
(完整word版)历年英语四级作文真题及范文解析(2004-)
2015年12月英语四级作文题目及范文解析汇总(第一套）For this part，you are allowed 30 minutes to write an essay commenting on the saying ”Learning is a daily experience and a lifetime mission.” You can cite examples to illustrate the importance of lifelong learning“。
You should write at least 120 words but no more than 180 words。
参考范文：Learning is a daily experience and lifetime mission.Undoubtedly， learning is a daily experience and lifetime mission. For instance， Madam Curie, who conducted pioneering research on radioactivity and became the first woman to win a Nobel Prize, was known for her persistence in learning。
Several reasons, both social and individual， could account for the importance of constant learning. Firstly， in an age of ruthless and relentless competition, only by learning constantly can we bring our potential and ability into full play and catch up with the times. Secondly， learning does not only help us acquire knowledge, but also enriches our lives and broadens our horizons. Thirdly，science and technology change with each passing day. Without constant learning，it would be impossible for us to update our knowledge.Accordingly， it is constant learning that really matters in achieving success in modern society。
大学英语四级考试历年作文（2006-2011）
大学英语四级考试历年作文（2006-2011）1、Students Selecting Their Lecturers2、Spring Festival Gala3、Welcome to Our Club4、Selecting Courses5、Recreational activity6、Limiting The Use of Disposable Plastic Bags7、Free admission to museums8、Creating a Green Campus9、Due Attention Should Be Given to Spelling10、How Should Parents Help Children to Be Independent大学英语四级考试2006年6月真题精讲：作文部分Part ⅠWriting (30 minutes)注意：此部分试题在答题卡1上。
Directions: For this part, you are allowed 30 minutes to write a short essay on the topic of Students Selecting Their Lecturers. You should write at least 120 words following the outline given below:1.有些大学允许学生自由选择某些课程的任课教师2.学生选择教师时所考虑的主要因素3.学生自选任课教师的益处和可能产生的问题Students Selecting Their Lecturers一、审题谋篇就体裁来说，本次四级作文为议论文，话题是关于学生自由选择某些课程的任课教师，属于校园类话题。
根据提示信息可以判断本文为提纲式作文，据此可以把文章分为三段。
首段介绍文章的主题“Some universities gi ve students freedom to choose their own lecturers for some courses”。
历年英语四六级作文真题范文及答案
历年英语四六级作文真题范文及答案Title: Previous years' English CET-4 and CET-6 essay questions, model answers, and explanationsIntroduction:English is an important subject for students in China, and the College English Test (CET) is widely used to assess students' English proficiency. Among the various sections of the test, the essay writing section is often considered challenging for many students. In this document, we will provide a collection of previous years' English CET-4 and CET-6 essay questions, model answers, and explanations to help students prepare for this section of the test.Essay Question 1 (CET-4):In recent years, the issue of environmental protection has become increasingly important. What do you think are the major causes of environmental problems? How can individuals contribute to environmental protection?Model Answer:Environmental problems are caused by a variety of factors, such as pollution, deforestation, and overpopulation. One majorcause of environmental problems is pollution, which is often a result of industrial activities and the burning of fossil fuels. Another cause is deforestation, which leads to loss of biodiversity and contributes to climate change. Overpopulation is also a significant factor, as it puts pressure on limited natural resources.Individuals can contribute to environmental protection in several ways. Firstly, individuals can reduce their carbon footprint by using public transportation, carpooling, or biking instead of driving. Secondly, individuals can conserve energy by turning off lights and appliances when not in use. Finally, individuals can support environmental organizations and participate in community clean-up events to help protect the environment.Explanation:This model answer effectively addresses the key points of the essay question by discussing the major causes of environmental problems and providing practical ways for individuals to contribute to environmental protection. The essay is well-organized and contains relevant examples to support each point.Essay Question 2 (CET-6):With the increasing use of social media, online relationships have become more common. Do you think online relationships are as meaningful as face-to-face relationships? Why or why not?Model Answer:Online relationships can be meaningful, but they are not necessarily the same as face-to-face relationships. While online relationships can provide a sense of connection and support, they may lack the depth and intimacy of face-to-face relationships. Face-to-face interactions allow people to read each other's body language and facial expressions, which can deepen the emotional bond between individuals.However, online relationships have their own advantages, such as convenience and accessibility. Online relationships can also be a valuable source of support for individuals who may not have access to face-to-face relationships. In the end, the meaningfulness of a relationship depends on the level of communication, trust, and understanding between individuals, whether they are online or offline.Explanation:This model answer provides a balanced view of online relationships compared to face-to-face relationships. It discussesthe advantages and disadvantages of both types of relationships and offers a nuanced perspective on the topic. The essay iswell-structured and uses logical arguments to support the author's viewpoint.Conclusion:In conclusion, practicing writing essays on a variety of topics can help students improve their writing skills and prepare for the essay writing section of the English CET-4 and CET-6 exams. By analyzing the model answers and explanations provided in this document, students can learn how to effectively address essay questions and develop their own writing style. With diligent practice and preparation, students can successfully tackle the essay writing section of the CET exams and achieve a high score.。
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历年英语四级真题作文范文汇总2012年6月大学英语四级作文真题Directions: For this part you are allowed 30 minutes to write a composition entitled On Excessive Packaging following the outline below.You should write at least 120 words but no more than 180 words.1.目前许多商品存在过度包装的现象2.出现这一现象的原因3.我对这一现象的看法和建议On Excessive PackagingI assume that you are familiar with the phenomenon of “Excessive Packaging”. Taking a look around，we can find examples with ease：a small computer is packed in a thick and heavycarton，clothes are putted in awell-designed plastic bagsand moon-cakes are usually placed in delicate boxes。
What are the causes of this problem? On the one hand, to earn more economic gains, a considerable number of manufactures usually wrap their products with unnecessary but appealing materials aiming at attracting customer’s attention , arousing their curiosity and then stimulating their purchasing desire. On the other hand, quite a few customers believe that the more delicate the package seems，the superior the quality will be,the notion has also encouraged the trend of excessive packaging。
To change this situation, I think we should take the following measures. First, laws must be made and implemented to impose restriction onexcessive packaging. Moreover, a public education campaign should be launched to arouse customers' consciousness that packaging doesn't equal to quality. Only in this way can we put an end to this trend.2011年12月大学英语四级作文真题For this part, you are allowed 30 minutes to write a short essay entitled Nothing Succeeds Without a Strong Will by commenting on the humorous saying, "Quitting smoking is the easiest thing in the world. I’ve done it hundreds of times." You should write at least 120 words but no more than 180 words.1.坚强的意志是成功的重要保证。
2.意志坚定的人才能完成伟大的使命。
3.学生也是这样，不刻苦学习，终究不会成为有用之才。
Noting Succeeds Without a Strong Will“Nothing Succeeds Without a Strong Will” is accumulated experience we inherited from our forefathers. It stands to reason that persistence is vital to success; nevertheless, one’s end can never be accomplished with the lacking firmness of will.A case in point is the quitting of smoking. On the eve of the World No-Tobacco Day this year, the Ministry of Education and Ministry of Public Health advocated that campus smoking-control intervention should be the forerunner of the nationwide smoking-control efforts, which, undoubtedly, has motivated the campaign of “Smoking-free School” that has been sweeping the whole of China. In the advance of the movement, the humorous saying has acquired a proverbial currency, “Quitting smoking is the easiest thing world. I’ve done it hundreds of time.” Obviously, wanting in perseverance, these smokers will never fulfill their purposes.From what have been discussed above, we can reasonably come to the conclusion that only those tough-minded people can reach the summit. Otherwise, even if you have tried hundreds of times, you are still at the foot of the mountain, admiring those successful climbers.2011年6月大学英语四级作文真题Directions：For this part, you are allowed 30 minutes to write a short essay entitled How Should Parents Help Children to Be Independent? You should write at least 150 words following the outline given below.1、现在网上购物已成为一种时尚2、网上购物有很多好处，但也有不少问题3、我的建议Online Shopping参考范文Online ShoppingThe newly coined term "shopping on line" may by no means sound strange to most people in this day and age. Rightly so, a majority of people consider "shopping on the internet" as a fashionable life style and a novel way of consumption。
There is no denying that shopping online has exerted a profound influence on our daily life . To begin with, shopping online enables consumers to save a great deal of time for the reason that we can buy anything we like anytime and anywhere. What's more, there are a such a huge number of discount goods on the internet that customers who have a poor financial situation may save a great deal of money. As the common saying goes, however,"every sword has two blades." shopping online has also imposed a negative impact on our life. Firstly, people may get a heavy loss on the condition that they purchase counterfeit goods. Moreover, good after-sale services are not usually guaranteed。
Due attention has to be paid to this phenomenon, from my perspective, firstly, as the coexistence of merits and demerits of online shopping, we should, therefore, make the best use of its fruits and avoid the opposite facets. Then, laws and regulation should be worked out and enforced to strengthen the supervision of online shopping. Only in this way can we benefit from online shopping without its undesirable effects.2010年12月大学英语四级作文真题Directions：For this part, you are allowed 30 minutes to write a short essay entitled How Should Parents Help Children to Be Independent? You should write at least 150 words following the outline given below.1. 目前不少父母为孩子包办一切2. 为了让孩子独立, 父母应该……How Should Parents Help Children to Be Independent?参考范文Help Children to Be IndependentThanks to the “family plan”policy,today in China many families have onechild.Loving and caring for children is an old Chinese tradition that has remainedfor thousands of years.But the children are spoilt so much that they have less independence.They rely on their parents in everything.That is bad for a child's growing.Therefore,parents should develop the children's independence instead of doing everything for them.There are some ways to help children to be independent.First of all,you should believe your children can do the things well.Second,give them more chances to practise,when they don't know how to do it,just tell them the way.Third,don't be afraid to see them fail.In the beginning,they may do something bad.But don't worry,just let them try again.They can do the work as well as you if given more time.To be independent is good for the children.A child who is independent will succeed easily in the future.2010年12月大学英语四级作文真题Due Attention Should Be Given to Spelling1.如今不少学生在英语(论坛)学习中不重视拼写2.出现这种情况的原因3.这种现象导致的结果范文参考：Due Attention Should Be Given to SpellingNowadays fewer and fewer students pay attention to their word-spelling. According to a recent survey, there is a dramatic increase in the number of students who can only imitate the pronunciation of a word but be incapable of spelling it. In this essay I will discuss the factors of this phenomenon and offer my own view on it。