请教NN们－这句什么意思？

GWD-5-Q35 to Q37:

      Even more than mountainside slides

      of mud or snow, naturally occurring forest

      fires promote the survival of aspen trees.

Line     Aspens’ need for fire may seem illogical

  (5)    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

(10)   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

(15)   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,

(20)   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

(25)   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

(30)   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.

请教NN们，highlight的部分是什么意思，我没看懂！

consists of dead cells, the aspen’s bark

is a living, functioning tissue that—along

with the rest of the tree—succumbs quickly

(10)   to fire.

虽然大部分树的树皮是由死细胞组成，A的树皮却是一个活的，运转着的组织--与该树的其它部分一样--很快就会被火搞死