There was a time before our ancestors smashed flint and steel together,
很久以前，我们的祖先还未将燧石和铁器互击，
when they felt the cold lack of fire in their lives.
他们因生活缺乏火而时感寒冷。
But anthropologists theorize that early hominids relied on lightning to cause forest fires,
但人类学家推论原始人类依赖闪电引发森林大火，
from which they could collect coals and burning sticks.
由此他们能收集木炭和燃烧的树枝。
Fire gave them the ability to cook food and clear land, and became central in many rituals and traditions.
火让他们能够煮食和清理土地，并成为很多仪式和传统的中心。
So instead of seeing forest fires as an exclusively bad thing, ancient humans may have learned to appreciate them.
所以古代人类并不完全视森林大火为坏事，且可能已知道要感谢它们。
Yet, it wasn't just humans who benefitted from these natural phenomena.
但并不只是人类受益于这种自然现象。
Even as they destroy trees, fires also help the forest themselves, however counterintuitive that seems.
即使大火烧毁树木，但同时也帮助森林本身这看来悖于常理。
In fact, several forest species, such as select conifers, need fire to survive.
事实上，许多森林树种，如高等的针叶树都需要火来生存。
But how can fire possibly create life in addition to destroying it?
但火如何既毁灭生命，又创造生命？
The answer lies in the way that certain forests grow.
答案在于这些森林的成长方式。
In the conifer-rich forests of western North America, lodgepole pines constantly seek the Sun.
在北美洲西部的针叶树林，美国黑松总设法寻求阳光。
Their seeds prefer to grow on open sunny ground,
它们的种子偏好生长于空旷多阳的土地，
which pits saplings against each other as each tries to get more light by growing straighter and faster than its neighbors.
幼树互相竞争试图挣得更多阳光，要比旁边的树生长得更笔直、更迅速。
Over time, generations of slender, lofty lodgepoles form an umbrella-like canopy that shades the forest floor below.
经年累月，一代代细长高耸的美国黑松形成伞状树冠，遮蔽下面的“地面层”。
