Scroll bar on coastal plain near Kotzebue, Alaska. Each separate zone of vegetation represents a different generation of vegetation growth triggered by a new disturbance.
(Photo by E. Wohl)
Riparian Vegetation in the Colorado Front Range
Riparian Vegetation Summary
(Information compiled by Lina Polvi)
According to Naiman et al. (2005), riparian areas are transitional semiterrestrial areas regularly influenced by fresh water, found next to flowing water. This vegetation zone serves several important functions, including buffering the stream from sediment input, providing nutrient input and shade for aquatic life, and important habitat through the intrinsic high biodiversity of the riparian area.
Riparian vegetation zonation in the Colorado Front Range will be a function of the vegetation zones found by elevation and the process domain. Riparian vegetation growth depends on a variety of abiotic controls: valley geometry, new depositional features, flow regime, slope, elevation, and aspect, among others. Lateral gradations, from mesic to xeric plants, occur next to the channel; a lateral zonation of early seral to late seral plant communities, occuring with certain disturbance types, is also visible (Naiman & Decamps 1997).
| Vegetation Zonation by Elevation | Role of Disturbance | Useful Links | References |
Vegetation Zonation - Elevation
Due to changes in climate, vegetation communities adjust with changes in elevation. The Colorado Front Range varies in elevation from approximately 1800 m (6000 ft) to above 4300 m (14000 ft). Because elevation dictates the climate, including precipitation regime, the plant communities change as we travel up in elevation and can be broken up into four ecotones: Lower Montane, Upper Montane, Subalpine, and Alpine tundra. Because the riparian zone is a transition zone between terrestrial and aquatic plant communities, the type of terrestrial plant community will also dictate the type of riparian vegetation that can be found at any elevation. Even in the riparian zone, we will see some terrestrial vegetation because it is a transition zone. The mountain front of the Colorado Front Range is at the Lower Montane ecotone, and the 2300 m hydroclimatic border is at the upper region of the Lower Montane zone. The unglaciated process domains will mainly be located in the Lower Montane. The glaciated process domains extend into the Alpine zone. However, the process domain found in the Alpine zone will mostly be colluvial hollows which do not often carry running water year-round; therefore, there will not be a large distinction between terrestrial and riparian vegetation in this zone.
Modified from Veblen & Lorenz (1991) with data from Polvi (in prep.) Vegetation types in blue are those likely to be found in riparian areas, and those in black are terrestrial. Elevations between ecozones are transitional zones between lower and upper ecozone.
Role of Disturbance
The disturbance regime of an area plays a large role in structuring the plant communities. In riparian areas, this interaction between hydrology and geomorphology plays the largest role in structuring vegetation (Naiman & Decamps (1997). Floods not only nourish existing riparian vegetation, but clear out old and dead vegetation to create new scour patches, which are necessary for many riparian seedlings. Riparian areas are perpetually in a state of secondary succession, where vegetation transitions from early to late seral stages. Vegetation systems tend towards a climax state or oscillate between alternative stable states, where changes are stochastic and also depend on interactions between biota. Because disturbance is an integral part of forming a riparian ecosystem, riparian ecosystems tend towards disequilibrium. Woody shrubs and trees, such as willows, cottonwoods and conifers, will serve as the climax state in Front Range riparian systems. The riparian vegetation distribution is driven by a tolerance to geomorphic and environmental conditions on one end of the stress-equilibrium gradient, and competition with other riparian plants on the other end of the gradient (Hupp & Osterkamp 1996). In arid and semi-arid regions, such as the Colorado Front Range, depth to groundwater and flow frequency are the limiting factors for riparian vegetation (Hupp & Osterkamp 1996).
Click a link below to learn more about riparian vegetation in each process domain:
| Colluvial Hollows | Ephemeral Channels | Glaciated Confined | Glaciated Partially Confined | Glaciated Unconfined | Unglaciated Confined | Unglaciated Partially Confined | Unglaciated Unconfined |