If you’re a homeowner, there’s nothing good about forest fires. But it may come as a surprise to learn that for some plant species, they’re essential. And one among them is the flagpole-shaped tree known as the Rocky Mountain lodgepole pine.
THE SKINNY ON LODGEPOLE PINES
If you’re a skier, you’re probably familiar with lodgepole pines. The tall, slender trees often serve as repositories for underwear tossed from the ski lifts. A common sight at higher elevations, the pines pierce the slopes like pencils, towering over other plants in the landscape.
According to the USDA Forest Service, the lodgepole pine is one of the most widely distributed tree species in western North America. The Rocky Mountain species, Pinus contorta latifolia, can be found in northwest Canada, the Black Hills of South Dakota and as far south as Colorado, central Utah and eastern Oregon.
Distribution map of the Rocky Mountain lodgepole pine
One glance up the mountain and there’s no mistaking their pure, dense stands. Lodgepole pines don’t leave much room for other species. In fact, their slender, reddish brown trunks are packed so tightly together that their lower branches self-prune as they grow. This gives them their distinctive pole-like shape.
Still, despite their impressive heights of 150′ or more, lodgepole pines seldom attain large diameters. In Utah, for example, some 50′ trees have diameters that measure just over 5 inches. In fact, lodgepole diameters rarely reach more than a scant 16 inches. Nevertheless, most trees enjoy a lifespan of 150 to 200 years, with some living for over 400.
IT’S ALL ABOUT THE CONES
So why do lodgepole pines like fire? It’s all about reproduction. As the name implies, all conifers reproduce from seeds that are housed in their cones. In the case of Rocky Mountain lodgepole pines, the seeds are located in cones on their uppermost branches. These cones can be either closed (serotinous) or open (non-serotinous).
Closed cone/Photo credit: Oregon State University Dept. of Horticulture
Open cone/Photo credit: Oregon State University Dept. of Horticulture
Moreover, depending on what has occurred in nature over time, the cone may shift from one type to the other.
ALL FIRED UP OVER SEROTINOUS CONES
Most lodgepole forests in North America were established because of fire, in particular in the Rocky Mountains. As a result, in areas prone to fires, lodgepole pines typically bear serotinous cones.
Why? Because a resin seals the serotinous cones’ scales shut and must be melted to open. Forest fires provide the high temperatures the cones need to release their seeds.
HOW FIRE CREATES LODGEPOLE FORESTS
Indeed, lodgepole pines are prolific seed producers, with some producing up to 9,000 cones in a single growing season. Moreover, their thin, finely-scale barked is highly susceptible to fire. Together, these two factors make them uniquely able to disperse a vast amount of seeds.
That being said, the trees often wait a long time for a fire. And that can lead to a large accumulation of seeds. Indeed, it’s not uncommon for multiple years’ worth of cones to build up on a tree. Luckily for the species, though, the average serotinous cone can remain on the tree for at least 15 years. And some last for decades.
Rocky Mountain National Park
In addition to unsealing its cones, fire creates the perfect soil for lodgepole seedlings. Rich in minerals and decomposed organic matter, these freshly-prepared ‘beds’ provide the perfect conditions for the winged seeds to root. As a result, lodgepole pines are often able to develop huge stands with great density.
New lodgepole pines establishing after fire
And with each new forest fire, the stands regenerate yet more stands and the cycle continues.
DID YOU KNOW?
The name ‘lodgepole’ refers to the use of the wood in teepees and lodges by native American people. Today, the tree is still a highly desirable source of timbers for rail fences, barns structures and log cabins.
Fence made from lodgepole timbers