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But as the trees' pine cones mature to release their twirling seeds,
但當這些樹木的球果成熟，釋放它們隨風旋轉的種子
this signals a problem for the lodgepoles' future.
這預示了美國黑松將面對一個問題。
Very few of these seeds will germintate in the cool, sunless shade created by their towering parents.
只有少數種子能在高聳母樹下的陰涼地方發芽。
These trees have adapted to this problem by growing two types of cones.
為適應這問題，這些樹木生長出兩種球果。
There are the regular annual cones that release seeds spontaneously,
一種是一般的年生球果，會自發釋放種子
and another type called serotinous cones, which need an environmental trigger to free their seeds.
而另一種是“晚熟球果”需要環境誘因來釋放種子。
Serotinous cones are produced in thousands,
樹木生長出數以千計的晚熟球果
and are like waterproofed time capsules sealed with resinous pitch.
它們被樹脂封實，如同防水的時空膠囊。
Many are able to stay undamaged on the tree for decades.
多數能夠留在樹上數十年，不受破壞。
Cones that fall to the ground can be viable for several years, as well.
這種球果掉落地上后，也可獨立存活數年。
But when temperatures get high enough, the cones pop open.
而當溫度夠高，這些球果便會裂開。
Let's see that in action.
讓我們看看實際發生情況。
Once it's gotten started, a coniferous forest fire typically spreads something like this.
當一場針葉林大火開始通常會如此蔓延開來。
Flames ravage the thick understory provided by species like douglas fir,
火焰燒毀茂密的“灌木層”，當中包括花旗松
a shade-tolerant tree that's able to thrive under the canopy of lodgepole pines.
花旗松耐蔭，能在美國黑松的樹冠下生長。
The fire uses these smaller trees as a step ladder to reach the higher canopy of old lodgepole pines.
大火利用這些小樹作階梯向上蔓延至以老美國黑松為主的“樹冠層”。
That ignites a tremendous crown fire reaching temperatures of up to 2400 degrees Fahrenheit.
引燃巨大的樹冠火火場溫度高達華氏2400度。
