GRE机经阅读44

卖萌的三爷UID: 3824208

Exotic insect pests can produce both short-and long-term effects on forest ecosystems. Short-term
effects include the disturbances directly associated with the action of the pest, which may cause
the defoliation, loss of vigor, or death of trees. Long-term effects are primarily mediated by changes
in tree species composition and the consequent alterations of forest structure, productivity, and
nutrient uptake. Exotic pests are more efficient than most abiotic disturbances (e.g., fire or wind) at
producing long-term changes in species composition. Pests often target specific tree species and,
if they become established, they usually remain as permanent components of the ecosystem.
Shifts in forest species composition ramify through the ecosystem in many ways because tree
species have different, often unique properties.

2. The author of the passage mentions the “unique properties” of tree species primarily in order to
help explain
A. why pests tend to target specific tree species
B. why pests can have long-term effects on entire ecosystems
C. how pests contribute to shifts in forest species composition
D. how pests are able to become established in an ecosystem
E. how some tree species are able to withstand the effects of pests

答案选C. 但是我不是很懂为什么不能选A, 为什么不能说因为每个都有unique properties, 所以pests often target specific tree species呢？

onelittlemajiaUID: 3795546

这个就定位最后一句
Shifts in forest species composition ramify through the ecosystem in many ways because tree species have different, often unique properties.
因为tree species have different, often unique properties， 所以Shifts in forest species composition ramify。。。
pests target specific tree不是作者想去解释的内容。可以说因为 pests target specific tree，specific tree have unique properties， 所以 forest species shifts

滚动的西瓜UID: 3799038

这中间不存在这个逻辑吧，Shifts in forest species composition ramify through the ecosystem in many ways because tree species have different, often unique properties.是说明，因为虫子在这些树上，所以会给整个生态系统带来的问题吧。

并不是解释“为什么”的句子啊

sadaharu0718UID: 3722589

我的理解是，因为森林系统里面的species都有各自的功能，一个萝卜一个坑，所以exotic pest虽然表面上只是改变了它的target species，但是无意中对整个森林系统都有影响。更通俗一点来说，就是牵一发动全身的后果。