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.
The author of the passage refers to "the bark of most trees" (line 6) most likely in order to emphasize the
定位到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 与大部分数目的死树皮细胞相比，aspen的树皮是活的功能性组织，连同树木的其他部位，受到火的袭击后都非常容易死掉。 A 正确 B 与文章内容相反，排除 C 与文章内容相反，排除 D 无关 E 无关
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