LIANE HANSEN, host:
From NPR News, this Weekend Edition. I am Liane Hansen. 20 years ago, fire burned over 1.2 million acres in the greater Yellowstone area. At the time, the public perception was that the park was being destroyed. It was misperception. This week, as our series on Yellowstone National Park continues, we examine why fire is important to the health of the park's ecosystem.
Mr. ROY RENKIN (Vegetation Management Specialist, Yellowstone National Park): The trees in this part of the world have evolved with fire because it has been such a frequent factor in influencing forest structure and function.
HANSEN: Roy Renkin is a vegetation management specialist in Yellowstone. He wears a ranger uniform, dark green pants and sage green shirt, but he wears a park service cap instead of the stereotypical Smokey Bear hat. Renkin meets us at the park's headquarters at Mammoth Hot Springs just inside the north entrance. He's taking us on a day-long tour of some of Yellowstone's forests.
(Soundbite of van door closing)
(Soundbite of car starting)
HANSEN: We pile into a big white van and drive south. Renkin has been with the park for decades and knows its terrain like he knows his own skin. Lodgepole pines dominate the landscape in Yellowstone National Park. Although the soil in this area is very poor because of the park's volcanic history, these pines are one of the few species of plants that thrive here. They are very tall and thin. The branches and green needles are only found at the top third of the tree, the crown. Renkin points out that their shape contributed to their name.
Mr. RENKIN: These very straight, limbless poles of the tree were favored in order to build the Native American lodges and teepees, that kind of thing, so hence the name lodgepole pines.
HANSEN: These trees produce what is known as serotinous pine cones. Resins hold the scales of the cone together, so they are tightly closed with the seeds inside. Those cones can stay in the trees' crowns for 30 to 50 years.
Mr. RENKIN: What's necessary for those cones to open up and release those seeds is the heat that's generated from a passing fire. Fire burns through those cone scales, or the resins that hold them together are melted away. The cone scales open up, and the seeds fall out.
HANSEN: Once they've fallen to the forest floor, the germination process begins quickly. So without fire, those seeds might never be released. But the heat from the fire does not penetrate more than a few centimeters into the ground.
Mr. RENKIN: So it's not as though the fire burns and the place is nuked. I mean, what we see above ground may look burned very badly, but there is a lot of activity, there is a lot of material below ground that right away starts to give rise to that re-establishment.
HANSEN; That material, nutrients in soil, helps give life to the next generation of trees. After the 1988 fires, Roy Renkin and his colleagues fanned out to five different sites around the park to figure out how many lodgepole pine seeds were laying on the ground.
Mr. RENKIN: We counted between 15,000 to 2 million seeds per acre on the ground after the fire passed over. We went back to those same sites the first year after the fire, and what we found was from 2,000 to 12,000 seedlings per acre.
HANSEN: The forest definitely has grown back in those previously burned areas. Views out over the valleys show an abundance of green. And 95 percent of those trees germinated in the first year after the fire. There are a few areas where the lodgepole pines and other plant communities struggle to return.
Occasionally, fire management techniques do more damage than the flames themselves. Roy Renkin stops the van at an area burned in 1953. To fight that fire, a bulldozer was brought in to scrape a fire line, which involves removing all the vegetation in hopes of stopping the fire's progress. The forest that burned around this line has since recovered. The line itself is almost barren.
Mr. RENKIN: The plant communities are not adapted to deal with the kinds of disturbances that we often associate with the firefighting effort. We scrape away that topsoil. We scrape away that seed source. When we do these kinds of activities and don't reclaim it, the plants can't respond to it. This scar created from this suppression effort will be evident for centuries, for 200 years.
HANSEN: Now, there is a growing effort to repair the man-made disturbances. Scraping back the topsoil gives the plant communities a good jump start into healing. It's an important lesson for the Park Service and has given fire ecologists a greater appreciation for how this ecosystem has adapted.
To see photos of Yellowstone's forests and to hear other stories in our series, visit our website, npr.org. Our series on Yellowstone National Park concludes next week, when we look to the future of the park and some of the challenges ahead.