For years, no, decades, the US Forest Service and National Park Service engaged in an extremely successful forest fire prevention campaign. That campaign used Smokey the Bear to spread the message, "Only you can prevent forest fires."
Well, that prevention campaign was successful, too successful. It succeeded to the point of allowing a huge buildup of dry fuels in the western United States' forests and national parks. The conflagration that consumed about 30% of Yellowstone National Park in 1988 was an example of what can happen when there is a lot of tinder dry fuel in the forests coupled with extremely dry weather. It's been very dry in the west for about the last 12 years now.
In the 1970s and 1980s, scientists began to understand much better the positive role of fire in our western ecosystems. The Rim Fire that has burned its way into Yosemite National Park is another example of just such a situation.
The linked article from NASA's Earth Observatory has some excellent high resolution images of the Rim Fire and the resulting smoke plume.
NASA Earth Observatory - Rim Fire
