Even more than mountainside slides of mud or snow, naturally occurring forest fires promote the survival of aspen trees. Aspens' need for fire may seem illogical since aspens are particularly vulnerable to fires; whereas the bark of most trees consists of dead cells, the aspen's bark is a living, functioning tissue that-along with the rest of the tree-succumbs quickly to fire.

The explanation is that each aspen, while appearing to exist separately as a single tree, is in fact only the stem or shoot of a far larger organism. A group of thousands of aspens can actually constitute a single organism, called a clone, that shares an interconnected root system and a unique set of genes. Thus, when one aspen-a single stem -dies, the entire clone is affected. While alive, a stem sends hormones into the root system to suppress formation of further stems. But when the stem dies, its hormone signal also ceases. If a clone loses many stems simultaneously, the resulting hormonal imbalance triggers a huge increase in new, rapidly growing shoots that can outnumber the ones destroyed. An aspen grove needs to experience fire or some other disturbance regularly, or it will fail to regenerate and spread. Instead, coniferous trees will invade the aspen grove's borders and increasingly block out sunlight needed by the aspens.


According to the passage, which of the following would occur if an aspen grove failed to regenerate periodically?


Individual aspens would cease to produce hormones.

Individual aspens would grow outward instead of upward.

The root system of the grove's clone would die.

The grove would lose its access to sunlight.

Soil conditions in the grove would become unfavorable for the growth of aspens.

考题讲解

此讲解的内容由AI生成,还未经人工审阅,仅供参考。

正确答案是 D。文章指出,如果不及时重新生长,这片杨树林会遭到其它针叶树的侵略,这些针叶树会堵死杨树所需的阳光。因此,选项 D 是正确的。

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Prep2008E1-RC