Ecology of Rocky Mountain National Park
With elevations ranging from 7,860 feet to 14,259 feet, Rocky Mountain National Park is one of the highest national parks in the United States. Rocky Mountain’s sixty mountain peaks over 12,000 feet high provide world attention-grabbing scenery
Established in 1915, Rocky Mountain National Park covers approximately 415 square miles and is home to diverse plant and animal life. Rocky Mountain hosts more than sixty species of mammals (including elk and moose), nearly 300 bird species, several amphibian, reptile, and fish species, and innumerable insects. With the park’s large elevation range, plants and animals have become well adapted to various mountain ecosystems.
The ecological diversity seen in Rocky Mountain National Park mirrors the broader Western landscape from Denver to northern Alaska. Such ecological diversity is caused in part by the presence of the Continental Divide that runs through the park. Continental divides are boundaries that separate a continent’s river systems. The Continental Divide in the United States separates the country into two main sections, driven by topography – or the shape of the land. A drop of water that falls to the west of the Continental Divide will eventually flow into the Pacific Ocean and a drop of water that falls to the east of the Continental Divide will eventually flow into what the Gulf of Mexico. This park contains a range of ecological zones that were uplifted by tectonic forces and eroded by ancient glaciers. Three main ecosystem define Rocky Mountain National Park, defined by altitude and the different species they support.
Montane (5,600-9,500 feet)
The meandering rivers, open meadows and hilly slopes of the montane ecosystem support the largest plant and animal diversity within the park. The complexity of the montane ecosystem is due in part to the rapid change in elevations over short distances. For example, in the central Rocky Mountains, for every 100-meter increase in elevation, the mean annual temperature decreases by about 0.6 degrees C and the growing season shortens by approximately a week. The distinct biodiversity differences of this ecosystem are also based on the direction of the slopes of the mountain. South-facing slopes get the most sunlight and therefore are able to support the most vegetation. For these montane south-facing slopes, there are often large ponderosa pines which are known as the indicator species of montane areas. These trees love space and spread out extensively, ultimately becoming giants with broad root systems able to withstand drought conditions. Ponderosa pines are the largest conifer trees in the park and can live to be over 400 years old. The trees have a number of unique features including bark color changes from gray brown to cinnamon-red and needles that release a sweet, brown-sugar scent when warmed by the sun. North-facing slopes are not subject to the same strong, drying sunlight as the south-facing slopes and therefore, the north’s soils contain more available water. The availability of water but competition for sunlight has resulted in trees tall, slender trees that grow closely together.
Species
Many species live either full time or seasonally in the montane ecosystem due to the more tolerant conditions. As the warmest and driest ecosystem of the Rocky Mountains, the dry and rocky soil supports drought tolerant and sun-loving plants. Plants that enjoy more water like the Mountain Iris, can find hospitable habitats in the moist montane meadows. Birds are common here, including Western Tanagers. These birds breed in Rocky Mountain National Park during the summer and migrate south to Mexico and Central America for the winter. Interestingly, Western Tanagers breed farther north than any member of its tropical family. Beyond Western Tanagers, many other species found in this ecosystem including mammals such as black bears, coyotes, mule deer, and porcupines.
Subalpine (9,000-11,000 feet)
The subalpine ecosystem, occurring below the alpine tundra but above closed forest ecosystems, is characterized by short, cool summers, long, cold winters and higher levels of precipitation. With average annual snow accumulation being five feet or greater, it is no wonder most of Colorado’s ski resorts exist in subalpine ecosystems. Snow can remain into the spring and even into summer under the protection of subalpine shaded forest. Within this ecosystem are high-elevation stunted tree clumps, open woodlands, and openings dominated by dwarf shrubs. In this ecosystem with elevations just below tree-line, evergreen trees flourish and cover the mountainsides. Beyond the evergreens are mountain lakes and wildlife hidden within Subalpine forests. Trees typical of a subalpine forest include the Engelmann spruce and subalpine fir. In lower-altitude subalpine forests, these species grow tall and straight in response to the harsh conditions found nearing treeline, these species grow to be shorter and more misshapen at higher altitudes.
Species
Despite the increasingly harsh conditions of the subalpine ecosystem, a wide range of species have still been able to survive here. Bird species such as the Clark’s Nutcracker, spend part of the year here. These birds have a very short migration, usually just changing elevations. During summer, the Clark’s Nutcrackers can be found in the subalpine ecosystem in groups of a whitebark or pine and move to lower elevation forests with higher seed availability in the fall. Mammals found in this region include snowshoe hares who are well-adapted to snowy conditions. These rabbits get their name from their large hind feet which are able to act like snowshoes to help the rabbits quickly run on top of the snow without sinking. This ecosystem has a wide range of species that live in the subalpine full time as part of their annual migration patterns.
Alpine Tundra (Above 11,000 feet)
Tundra, meaning “land of no trees” does not mean it is without biodiversity. One of the most unique features of the Rocky Mountain National Park is the large amount of land above treeline - approximately one third of the park’s area! The strong solar radiation, high winds, and cold temperatures here make this an extreme climate, known for stunted tree growth.
Krummholz
At treeline (11,000-12,000 feet), tree growth is typically more horizontal than vertical. Subalpine fir, spruce, and whitebark pines, found in subalpine ecosystems, huddle and become islands called krummholz (German for crooked wood). Krummholz form is an adaption the trees have developed to survive in the cooler tundra climate by having lower branches that take root closer to the ground in order to grow more horizontally than vertically. Krummholz trees that are well established in the park may be hundreds to a thousand years old. For example, the Limber Pine tree species are shaped by the wind by twisting and clinging to rocky outcrops in some of the most windy corners of Rocky Mountain National Park. The name Limber Pine refers to its relationship with the wind as it describes the flexibility of the branches.
Species
The harsh conditions of this ecosystem are not uninhabitable for all organisms, with some species even thriving here. The yellow-bellied marmot is an example of an animal that is well-adapted to these conditions. These mammals, who are the largest members of the squirrel family, dig mazes of burrows beneath high-elevation meadows and rocky fields where they are protected from predators and extreme conditions. As a survival strategy for the extreme tundra winters, yellow-bellied marmots hibernate up to 200 days per year. Additionally, mammals such as elk move seasonally based on food availability living in the higher elevations during the summer and move to lower elevations during the winter.
Plant growth
The cold temperatures and frequent strong winds limit plant growth in this ecosystem. Plant species are usually small and grow low to the ground. In response to the cold, these plants are typically perennials. Short growing seasons allow plants to pollinate and grow very quickly. Tundra flowering plants are known for their adaptions to allow them to live in this harsh region. For example, many flowering plants have dense stem and hairy leaves that provide wind protection or red-colored pigments that help convert sunlight into heat. Plant species include the Alpine Forget-me-not, known for its fragrance and bright colors, and short stems (typically less than an inch tall). The majority of Rocky Mountain alpine plants evolved from Arctic species or regional high-elevation species already adapted to tolerate cold, high elevations. While the strong winds and cold temperatures make tundra vegetation seem tough, tundra plants can be very fragile to human touch. Repeated footsteps damage the plants and expose the soil to erosion.
