|
TOEFL READING
2001-07-06 10:17:23
Growing tightly packed together and collectively weaving a dense canopy of branches, a stand of red alder trees can totally dominate a site to the exclusion of almost everything else, certain species such as salmonberry and sword ferns have adapted to the limited sunlight dappling through the canopy, but few evergreen trees will survive there; still fewer can compete with early prodigious growth of alders. A Douglas fir tree reaches its maximum rate of growth ten years later than an alder, and if the two of them begin life at same time, the alder quickly outgrows and dominates the Douglas fir, after an alder canopy has closed , the Douglas fir suffers a marked decrease in growth, often dying within seven years. Even more shade-tolerant species of trees such as hemlock may remain badly suppressed beneath aggressive young alders.
Companies engaged in intensive timber cropping naturally take a dim view of alders suppressing more valuable evergreen trees. But times are changing; a new generation of foresters seems better prepared to include in their management plans consideration of the vital ecological role alders play.
Among the alder's valuable ecological contributions is its capacity to fix nitrogen in nitrogen-deficient soils. Alder roots contain clusters of nitrogen-fixing nodules like those found on legumes such as beans. In addition, newly developing soils exposed by recent glacier retreat and planted with alders show that these trees are applying the equivalent of ten bags of high-nitrogen fertilizer to each hectare per year. Other chemical change to soil in which they are growing include a lowering of the base content and rise in soil acidity, as well as a substantial addition of carbon and calcium to the soil.
Another important role many alders play in the wild, particularly in mountainous areas, is to check the rush of water during spring melt. In Japan and elsewhere, the trees are planted to stabilize soil on steep mountain slopes. Similarly, alders have been planted to stabilize and rehabilitate waste material left over from old mines, flood deposits, and landslide areas in both Europe and Asia.
tightly : ad. 紧紧地,坚固地
pack : n. 包裹,一群,一副,背包,包装;vt. 包装,捆扎,塞满,压紧,挑选;vi. 包装货物,挤,群集,被包装;背包
collective : a. 集体的,聚集的,共同的
weave : n. 编法,织法,编织;vt. 编织,组合,编排,使迂回前进;vi. 纺织,迂回行进,摇晃
dense : a. 密集的,浓厚的
canopy : n. 天篷,遮篷,苍穹;vt. 用天蓬遮盖
alder : n. 桤木
dominate : vt. vi. 支配,占优势
exclusion : n. 排除,除外,逐出
sword : n. 刀,剑,战争,武力
fern : n. 蕨类植物
adapt : vt. 使适应,改编;vi. 适应
dapple : n. 斑纹,花马;a. 有斑纹的;vt. vi. (使)起斑纹
survive : vt. 生存,生还,幸免于;vi. 活下来,幸存
prodigious : a. 很大的,惊人的,异常的
fir : n. 枞树,杉木
maximum : n. 极点,最大量,极大;a. 最高的,最大的,最大极限的
outgrow : vt. 过大而不适于,出生,长出
suffer : vt. 遭受,经验,忍受;vi. 受痛苦,受损害
decrease : n. 减少,减少之量;vi. vt. 减少
tolerant : a. 宽容的,宽大的,默认的
hemlock : n. 毒胡萝卜,铁杉
suppress : vt. 镇压,使止住,禁止,抑制,查禁
aggressive : a. 侵略的,攻击性的,进取的
engage : vi. 答应,从事,交战;vt. 使忙碌,雇佣,预定,使从事于,使参加
intensive : a. 加强的,集中的;n. 加强器
timber : n. 木材,木料;vt. 用木材建造
croppy : n. 剪短发的人
dim : a. 暗淡的,模糊的;vt. 使暗淡
generation : n. 一代,一世,产生
forester : 林业居民；护林人员；林业动物
consideration : n. 考虑,原因
vital : a. 重要的,生命的,充满活力的,生死攸关的,致命的
ecological : a. 生态学的,社会生态学的
contribution : n. 捐助,捐助之物,贡献
capacity : n. 容量,能力,才能,资格;n. 容量
nitrogen : n. 氮
deficient : a. 不足的,不充分的,有缺陷的
cluster : n. 串,丛,群,簇;vi. 成串,丛生;vt. 使聚集
nodule : n. 小节,小瘤,小结节
legume : n. 豆类,豆荚
exposed : a. 暴露的,无掩蔽的,暴露于风雨中的
retreat : n. 休息寓所,撤退,隐居,退避,避难所;vi. 撤退,隐退,放弃,向后倾;vt. 退(棋)
equivalent : n. 同等物,等价物,相等物;a. 相等的,相当的,同意义的
fertilizer : n. 肥料,受精媒介物
hectare : n. 公顷
lowering : a. 使卑劣的,减弱体力的,昏暗的
substantial : n. 重要部分,本质;a. 实质上的,物质的,有内容的,结实的
carbon : n. 碳,副本,复写纸
calcium : n. 钙
melt : n. 熔化,熔化物,溶解;vt. vi. (使)熔化,(使)溶解,(使)消散,(使)变软
stabilize : vt. 使安定,使坚固;vi. 稳定,安定
steep : n. 浸渍,浸液,悬崖;a. 险峻的,陡峭的,急剧升降的,不合理的,夸大的;vt. vi. 浸,泡
slope : n. 倾斜,斜坡,斜率,掮枪的姿势;vt. 使倾斜,弄斜,掮;vi. 倾斜,逃走
rehabilitate : vt. 恢复原状,修复,使恢复
flood : n. 洪水,大量之水,涨潮;vt. 使泛滥,注满,淹没;vi. 被淹,溢出,涌进
deposit : n. 存款,定金,堆积物;vt. 存放,堆积;vi. 沉淀
landslide : n. 山崩 推荐给好友  打印本页
|
All
rights reserved.
