Ecologists Watch Land Change

I think that when we look at the last hundred years of fire suppression, removing fire from the ecosystem has been the most radical management choice we could have made.

When the settlers arrived, they saw open, park-like stands of huge ponderosas with grass and wildflowers growing underneath. I'd like to see us return to this historic ecosystem where fire can play the natural role it has before. Many plants and animals are adapted to fire just as they are to rain and sun.

For the ecosystem to function well, it needs diversity. Forestry has focused on efficiency for a long time, but now we're seeing that a forest that grows only one kind of economically valuable tree isn't a healthy forest. The conditions here in the northern Rockies are too marginal to turn the land into a tree farm. We really need to be high-tech hunter-gatherers, taking a sustainable amount from a system that can run by itself.

To do that, we must return fire to the landscape. Low-intensity fires that just burned up the grass and brush came through the Ponderosa pine habitat on an average of every 15-50 years. Enough Ponderosa seedlings survived to replace the big trees when they died. Game animals were attracted to the grass, and these forests were favorite Indian hunting grounds.

High density stands lead to bark beetle infestation and stress. Douglas-fir gets dwarf mistletoe, which deforms the tree, and root rot, which kills it.

Leaving these stands alone as they are now won't let large trees keep growing. They'll just keep dying. Thinning lets a few larger trees get the water and light they need to thrive. Fire stimulates the ponderosas to produce pitch, which makes the wood harder. Since it's so dry here, woody debris rots slowly. Fire recycles nutrients more rapidly.

Old growth ponderosas got big back when regular fires kept the competition down. We might think we are saving timber for the future by keeping fire away. But in fact, the big trees haven't grown much since the Douglas-fir started coming up. They're just standing there, waiting for the chance to grow some more.

But time is running out. The ponderosas are stressed for water and light and will eventually die. If there is a fire, it is much more likely to be a destructive "stand replacement" burn, where everything will be killed and start over from scratch.

Fire does more than just clean up the mess of brush and slash. It shapes the entire ecosystem. For example, there's a shrub called bitterbrush that elk really like to eat. It's been declining where there's been no fire.

It turns out that the bitterbrush depends on deer mice and chipmunks to husk and plant its seeds for it. But when a deep layer of needles and duff accumulates because of fire suppression, the mice take the bitterbrush seeds down into their burrows. The seeds won't grow there.

There's a different problem in second-growth stands. Since all the trees are about the same age, there isn't much diversity in the stand. That means fewer different little habitats for animals and other plants. If the stand stays this dense, no new trees will be able to grow.

There isn't enough water for all the trees, and when they're stressed, they can't fight disease as well. For example, a healthy ponderosa can drown bark beetles in pitch when the beetle bores into the tree. A thirsty tree can't do this, and the beetle has no trouble getting in and laying its eggs. The grubs then eat the thin layer of live wood and eventually kill the tree.

Opening up the stand is really just the beginning of a long process to restore it. Because the existing ponderosas are so stressed, many of them won't make it. And the Douglas-fir that will be left do not survive fire well, no matter how big they are.

Ponderosa need light to grow, so the fastest way to bring them back would actually be to open up larger patches -- say an acre or so -- and then plant ponderosa and larch in these areas. But that's not very popular with the public, since it looks like a clearcut to a lot of folks.

Steve Arno
fire ecologist