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But as the trees' pine cones mature to release their twirling seeds,
但当这些树木的球果成熟，释放它们随风旋转的种子
this signals a problem for the lodgepoles' future.
这预示了美国黑松将面对一个问题。
Very few of these seeds will germintate in the cool, sunless shade created by their towering parents.
只有少数种子能在高耸母树下的阴凉地方发芽。
These trees have adapted to this problem by growing two types of cones.
为适应这问题，这些树木生长出两种球果。
There are the regular annual cones that release seeds spontaneously,
一种是一般的年生球果，会自发释放种子
and another type called serotinous cones, which need an environmental trigger to free their seeds.
而另一种是“晚熟球果”需要环境诱因来释放种子。
Serotinous cones are produced in thousands,
树木生长出数以千计的晚熟球果
and are like waterproofed time capsules sealed with resinous pitch.
它们被树脂封实，如同防水的时空胶囊。
Many are able to stay undamaged on the tree for decades.
多数能够留在树上数十年，不受破坏。
Cones that fall to the ground can be viable for several years, as well.
这种球果掉落地上后，也可独立存活数年。
But when temperatures get high enough, the cones pop open.
而当温度够高，这些球果便会裂开。
Let's see that in action.
让我们看看实际发生情况。
Once it's gotten started, a coniferous forest fire typically spreads something like this.
当一场针叶林大火开始通常会如此蔓延开来。
Flames ravage the thick understory provided by species like douglas fir,
火焰烧毁茂密的“灌木层”，当中包括花旗松
a shade-tolerant tree that's able to thrive under the canopy of lodgepole pines.
花旗松耐荫，能在美国黑松的树冠下生长。
The fire uses these smaller trees as a step ladder to reach the higher canopy of old lodgepole pines.
大火利用这些小树作阶梯向上蔓延至以老美国黑松为主的“树冠层”。
That ignites a tremendous crown fire reaching temperatures of up to 2400 degrees Fahrenheit.
引燃巨大的树冠火火场温度高达华氏2400度。
