The vitality of the forests in Rocky Mountain National Park depends on fire. Fire removes the thick layer of decaying vegetation on the forest floor. Herbaceous plant growth enhances and the nutrients that were tied up in the litter are released. Fire also creates a mosaic of different types and ages of forest vegetation. This improves habitat and increases the diversity and abundance of wildlife.
Research in fire ecology has demonstrated that many plant and animal species actually benefit from the rejuvenating effects of fires burning regularly through their habitat. Without fire, forests would not be able to support the diverse habitats required by many plant, bird and mammal species.
Fire has a different role in each forest type covering the park’s mountain slopes.
Mountain forests of ponderosa pine and Douglas fir are found at an elevation of 6,000 feet (1,829m) to as high as 9,000 feet (2,743m). Lightning-caused surface fires are a natural part of this ecosystem. Frequent surface fires burn grass, pine needles, and dead wood; but rarely kill the older thick-barked trees.
By killing tree seedlings, ground fires maintain the natural openness of these woodlands decreasing the probability of hot crown fires. The grasses, shrubs, and wildflowers which grow in the openings between trees, make excellent forage for wildlife. Ponderosa pines in open stands are healthier and can resist the invasion of the wood-boring mountain pine beetle by forcing them out with sap.
Lodgepole pine forests cover large areas of the park between about 8,500 and 10,000 feet (2,591 and 3,200m). These forests depend on fire. Lodgepole pine are tall trees that can grow in extremely dense stands to the exclusion of other species. This is partly due to the fact that these trees are prolific seed producers.
Lodgepole pine trees have serotinous (closed) cones that produce hundreds of thousands of seeds. Sealed with a dense resin, the closed cones may remain on the tree for decades until a fire sweeps through. High fire temperatures over 100 degrees Fahrenheit melt the resin opening most of these cones to release their seeds. The bare mineral soil and fresh ashes produced by a fire provide an excellent seedbed for lodgepole pine seedlings to grow in the open sunshine.
Engelmann Spruce and Subalpine Fir
Subalpine forests of Engelmann spruce and subalpine fir can reach 300 to 400 years of age below treeline elevations of 11,400 feet (3,475m). These cool, moist forests receive more snow than any other mountain zone. Snow pack remains well into the summer.
As the snow melts, water is stored in the soil. This moisture together with that from summer thunderstorms helps make spruce-fir forests fire resistant. Studies of tree rings indicate a fire only once every 300 years or more.
Fire affects deciduous trees, such as aspen. After a fire, aspens sprout from their roots and spread more easily. Aspen suckers initially outgrow slower developing conifers and can dominate areas for many years after a fire. Eventually these trees are replaced by more shade-tolerant species.
Aspen forests provide habitat for a rich variety of life. When aspen return to a burned area, so do the accompanying plants and animals that depend on this type of habitat.