What is the central argument of the passage?

Some trees depend on fire, and decades of preventing fire made the later fires worse. (The first two paragraphs show trees that need fire; the third shows what happened when fire was removed. The argument joins the two.)

What makes the lodgepole pine's sealed cones open?

heat, which melts the resin holding them shut (The passage says the cones are sealed with resin and that only heat melts the seal.)

Why did fighting every fire fail to make the forests safer?

The fuel that small fires would have removed built up until the fires that came were far hotter. (The passage lists dead wood building up and young trees crowding in, then says the eventual fires were hotter and harder to stop. The closing line calls this saving disturbance up.)

In "seedlings cannot start in deep litter", the word "litter" means

the layer of dead needles and leaves lying on the ground (The next sentence says fire burns off the layer of dead needles, which is the same thing named again. So litter here is fallen plant material.)

Forests That Need Fire: Level 4 Reading Comprehension Questions

Some trees do not merely survive fire; they wait for it. The lodgepole pine seals many of its cones shut with resin, and those cones can hang closed on the branch for years. Only heat melts the seal. When a fire passes, the cones open and drop their seed onto ground that has just been cleared of competitors and dusted with ash. A disaster, from the seed's point of view, is a delivery.

The giant sequoia depends on the same arrangement and on a second favour. Its seedlings cannot start in deep litter or in shade; they need bare soil and open sky. Fire supplies both, burning off the layer of dead needles and thinning the smaller trees that would otherwise close the roof of the forest.

This explains an uncomfortable result of good intentions. For much of the twentieth century, fire in North American forests was fought wherever it appeared. The forests did not become safer. Dead wood built up year after year, young trees crowded in, and the fires that finally came were hotter and harder to stop than the ones that had been prevented. Removing a frequent small disturbance did not remove disturbance. It saved it up.

Comprehension questions