Forests Shaped by Fire
Fire has a different role in each forest type that covers the park’s mountain slopes.
From the foothills, at an elevation of 6,000 feet (1,829m) to as high as 9,000 feet (2,743m), mountain forests of ponderosa pine and Douglas fir are found. 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.
Between about 8,500 and 10,000 feet (2,591 and 3,200m), lodgepole pine forests cover large areas of the park. These forests depend on fire. Sealed with a dense pitch, the closed cones may remain on the tree for decades. High temperatures are required to open most of these cones and release their seeds. The bare mineral soil and fresh ashes produced by a fire provide an excellent seedbed for lodgepole pine seedlings.
Below treeline, at an average elevation of 11,400 feet (3,475m), subalpine forests of Engelmann spruce and subalpine fir can reach 300 to 400 years of age. 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 other trees, such as aspen. After a fire, aspens sprout from their roots and spread more easily.
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 is enhanced 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.
Did You Know?
Temperature causes tree line. Trees need an average growing temperature of about 50 degrees fahrenheit.