Forestry Forest Fire Listen again to part of the talk. Then answer the question. What does the instructor mean by this statemen

We all know that change is a fact of life. For North American forests, change often comes in the form of fire. After thousands of years of living with fire, many plant and animal species have come to depend on its periodic presence. Without fire, ecosystems can stagnate and lose their diversity of life.
In the past, before we understood the role that fire plays in the natural life cycle of our forests, our goal was to prevent or contain all forest fires. For almost ninety years, our land management agencies tried to eliminate fires. In many cases, we protected the trees, but at the expense of the forest community. Now we know that fire is a natural agent that rejuvenates a forest. And we know that fire suppression can actually threaten the lives of healthy trees. So, today our policy is to allow natural fires to burn under close observation and to set "prescribed" fires under carefully controlled conditions.
Research shows that forests go through natural fire cycles. Periodic fires are necessary for several reasons. Fire removes nutrients from standing dead trees and returns them to the earth, where they become available to the root systems of new trees. Fire also opens the forest to sunlight. Openings in the tree cover benefit a variety of wildlife by stimulating the growth of lush green plants, which are eaten by several species of animals.
Fire is nature’s way of controlling insect infestations. By contrast, fire suppression preserves dead wood that harbors insect pests, like the larvae of the mountain pine beetle. These beetle larvae feed on the inner bark of some trees, which blocks the flow of nutrients and eventually kills the trees. When dead trees burn during periodic outbreaks of fire, the heat kills off great numbers of beetles and larvae, providing a natural method of pest control.
The exclusion of fire from the ecosystem is creating unhealthy, overcrowded forests that contain more fuel for larger, more severe fires. For example, when a huge fire threatened a grove of giant sequoias in California, observers noted that the flames were fed by dead wood and combustible debris that had accumulated on the forest floor over years of fire suppression.
A large-scale, intense forest fire causes more significant impacts to water, soil, and air resources than a managed prescribed fire. Prescribed fire, or controlled fire, has several purposes. Chiefly, it reduces the hazard of more serious wildfires by periodically burning accumulated weeds, brush, and other plants. If done carefully, prescribed burning also releases nutrients back into the soil and controls insect pests. In Florida, prescribed burns are carried out every three to five years in one of the national forests. These controlled burns keep the forest open and reduce the growth of problem species.
We recognize that fire is a natural and revitalizing process that enhances the diversity of the forest. However, we also know that fire has consequences. There may be smoky, hazy skies and patches of blackened forest for a long time after a fire. There’s also the risk of a fire becoming too large and threatening inhabited areas. But we have to accept these realities if our forests are to retain their ecological balance.