首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
The forest from which Man takes his timber is the tallest and most impressive plant community on Earth. In terms of Man’s brief
The forest from which Man takes his timber is the tallest and most impressive plant community on Earth. In terms of Man’s brief
admin
2010-01-26
43
问题
The forest from which Man takes his timber is the tallest and most impressive plant community on Earth. In terms of Man’s brief life it appears permanent and unchanging, save for the seasonal growth and fall of the leaves, but to forester it represents the climax of a long succession of events.
No wooded landscape we see today has been forest for all time. Plants have minimum requirements of temperature and moisture and, in ages past, virtually every part of Earth’s surface has at some time been either too dry or too cold for plants to survive. However, as soon as climatic conditions change in favour of plant life, a fascinating sequence of changes occurs, called a primary succession.
First to colonize the barren land are the lowly lichens, surviving on bare rock. Slowly, the acids preduced by these organisms crack the rock surface, plant debris accumulates, and mosses establish a shallow root-hold. Ferns may follow and, with short grasses and shrubs, gradually form a covering of plant life. Roots probe even deeper into the developing soil and eventually large shrubs give way to the first trees. These grow rapidly, cutting off sunlight from the smaller plants, and soon establish complete domination-closing their ranks and forming a climax community which may endure for thousands of years.
Yet even this community is not everlasting. Fire may destroy it outright and settlers may cut it down to gain land for pasture or cultivation. If the land is then abandoned, a secondary succession will take over, developing nmch faster on the more hospitable soil. Shrubs and trees are among the early invaders, their seeds carried by the wind, by birds and lodged in the coats of mammals.
For as long as it stands and thrives, the forest is a vast machine, storing energy and many elements essential for life.
Why is a "secondary succession" quicker?
选项
A、The ground is more suitable.
B、There is more space for new plants.
C、Birds and animals bring new seeds.
D、It is supported by the forest.
答案
A
解析
从第四段的中间,我们可以看出,根本的原因乃是土壤较为适宜。
转载请注明原文地址:https://kaotiyun.com/show/60dK777K
0
大学英语六级
相关试题推荐
Globalwarmingreferstotheaveragetemperatureoftheatmosphere,oceans,andlandmassesofEarth.Todayatmosphericcarbond
Globalwarmingreferstotheaveragetemperatureoftheatmosphere,oceans,andlandmassesofEarth.Withoutgreenhouseeffect,
Globalwarmingreferstotheaveragetemperatureoftheatmosphere,oceans,andlandmassesofEarth.Theaveragesurfacetemper
Globalwarmingreferstotheaveragetemperatureoftheatmosphere,oceans,andlandmassesofEarth.Toagreatextent,therap
Accordingtothepassage,fightingagainstgreenhouseeffectsuccessfullyrequires______.Theemission-tradingprogramwoulde
A、Hethinksflieswilltakeovertheearth.B、Hethinkshumanwilldieoffquitesoon,C、Hethinksmassdiseasecouldbethenex
Whetherthepastornow,parentlesschildrenrelyonthegoodwillandpityofthecommunity.Tobecomeafosterparent,onenee
Forthispart,youareallowed30minutestowriteashortessayentitledFightingCorruption.Youshouldwriteatleast150wor
Theoldestandsimplestmethod,then,ofdescribingdifferencesinpersonalitywasto(36)______peopleaccordingto(37)______
随机试题
男,40岁,急性肠梗阻2天,伴呕吐频繁、乏力、口渴、尿少、口唇干燥、眼窝下陷、皮肤弹性差,脉搏116次/分钟。化验:Hb163g/L,血细胞比容0.55,血清钠140mmol/L,血清钾4mmol/L。治疗措施应是
男性,45岁,因骨盆骨折住院。X线检查发现多部位溶骨性病变。实验室检查:骨髓浆细胞占25%,红细胞沉降率50mm/h,血红蛋白为80g/L,尿本周蛋白阳性,血清蛋白电泳呈现M蛋白,血清免疫球蛋白含量IgG8g/L、IgA12g/L、IgM0.
A.贫血重而出血轻B.贫血与出血相一致C.贫血轻而出血重D.有贫血而无出血E.无贫血而有皮下出血31.缺铁性贫血特发性血小板减少性紫癜
喷砂抛光机器的气源压力范围是
2011年7月11日,A市升湖区法院受理了黎明丽(女)诉张成功(男)离婚案。7月13日,升湖区法院向张成功送达了起诉状副本。7月18日,张成功向升湖区法院提交了答辩状,未对案件的管辖权提出异议。8月2日,张成功向升湖区法院提出管辖权异议申请,称其与黎明丽已
国家重要景区的详细规划,由()。
为保证会计工作正常进行和会计信息的质量,对会计工作人为假设的基本前提有()。
C集团公司正面临着一项困难的供应商抉择——复印机租赁合同的竞争者有5家,5家公司给出的报价相差不大,集团公司以前也并没有与任何一家有过合作关系。如果签订的采购合同不公平,日后势必出现一些消极的影响,不利于集团公司的采购业务。公司必须权衡许多问题,并承诺在3
设,若,则该幂级数的收敛半径等于__________.
设某种零件的长度L~N(18,4).从一大批这种零件中随机取出10件,求这10件中长度在16~22之间的零件数X的概率分布.数学期望和方差.
最新回复
(
0
)