Note: This article is a sidebar to this issue's feature story.
If you watched the Yellowstone fires in 1988, you’ve seen lodgepole pine in action. This is a tree that is built to burn. It grows in dense thickets at high elevations where the climate is usually moist and cool. But when drought and high winds come together, a mountainside can burn in a day. Lodgepole burns hot and fast, typically every 100 to 200 years. Fire opens the tree’s pitchy "serotinous" cones, which release their seeds, starting the process over again.
When it comes to surviving ground fires, this species could be called the "asbestos pine." The outer layer of its thick bark actually springs off the tree when ignited, carrying the flame yards away. Its roots run deep so they seldom burn out, while exceptionally long needles reflect heat away from large, moist buds. The ponderosa isn’t immune to crown fires, however, and it is at a decided disadvantage after such a fire burns through. Its heavy seeds seldom disperse farther than 100 yards, and since it doesn’t grow well in shade, the ponderosa is squeezed out if periodic ground fires don’t kill off other species as the forest regenerates.
Aspen trees hide their fire protection underground. Each tree is actually a clone growing from the same root system as those around it. When fire levels a stand of aspen, the roots generate more stems that can quickly outgrow any competitor. But aspen won’t grow in shade, and the new stems grow only if ground fire weeds out upstart coniferous trees. As a result of fire suppression, aspen numbers have decreased dramatically across the West.
Like aspen, whitebark pine colonizes burned areas, but where aspen springs back from the ground, the whitebark sends its seeds to the sky. Found on high mountaintops and ridges, this tree grows its cones upside down, so the seeds never drop directly to the ground. That would be useless, since the tree won’t grow in shade. Instead, the bird called Clark’s nutcracker collects them, caching them in recently burned areas. When the bird returns to snack, it always overlooks a few seeds, which end up germinating.
If you were a ponderosa pine, your biggest complaint would be about how those Douglas firs are always moving into the neighborhood. The Dougs, who don’t mind being the underdog, fare well in shaded forests as they slowly reach up from the understory to the forest canopy. Unless frequent ground fires clear them out, Douglas firs will shade out young ponderosas and help carry fire from the forest floor to the tops of the large pines, turning what might have been an innocuous ground fire into a full-blown conflagration.
PACIFIC SILVER FIR
Everyone knows it rains a lot in the Pacific Northwest. That’s why the Pacific silver fir grows well there; you don’t get wildfires every summer. But watch out when severe drought hits the area — say, every 300 to 500 years. Once they dry out, the silver firs provide highly flammable fuel for wind-driven crown fires. Then it’s time to get out of the way.
Pygmy forests, dwarf woodlands — that’s what silviculturalists call a landscape that is dominated by piñon pine and juniper trees. These short, bushy trees grow at mid-elevations from Oregon deep into Mexico. Think dry, hot country. Usually the trees don’t burn easily until drought hits, when fires burn up some stands, while picking their way through others. Historically, fire used to regularly thin p-j forests, but not anymore. Cows eat much of the grass that grows amid the trees, removing the light fuels that allowed the spread of low-intensity fire. Now there are more p-j woodlands than ever before.
Copyright © 2001 HCN and Mark Matthews