Lower Montane – Foothill Shrubland

In Colorado, altitude plays a dominant role in determining where one finds different plant communities. At the lowest altitudes, the dominant plant community on the eastern slope is grasslands. Our grasslands on the Great Plains are hot and dry with fine soils. The only place that one finds shrubs or trees here is in damp areas along streams, or rocky outcrop areas.

As one moves up in altitude into the foothills and lower montane, however, the climate is less dry, and the soil is rockier. Both of these factors begin to favor the presence of shrubs. Move up further where the climate is even wetter, and one will find forests.

Rocky Mountain Lower Montane—Foothill Shrublands occur in that mid-range between the grasslands on the plains and forests in the montane. They are found in the foothills from 4,900 feet to the lower slopes in the montane up to 9,500 feet, but also can be found on canyon slopes, rock outcrops and mesas on the eastern plains of Colorado. All of these areas are characterized by exposed, dry, rocky substrates where it is too dry for trees to grow, and too rocky for grasslands to occur.

This community ranges from southern New Mexico, through the front range of Colorado and north to Wyoming, and also occurs on the Colorado western slope and the inter-mountain region. It is distinct from the Gambel Oak shrubland community, discussed on this website, by the absence, or very low presence (<5%) of Gambel Oak. Gambel oak shrublands generally grow in more mesic conditions. This habitat may include some patches of trees (Juniperus scopulorum, Pinus ponderosa) as well as grassy areas, but otherwise the dominant structure is shrubs.

Fire also plays an important part in this plant community because it maintains shrublands by eliminating the growth of trees. Most of its dominant shrubs, except Purshia tridentata, experience severe die-back from fire, but are able to survive by resprouting vigorously afterwards, or sprout from seed. The dominant shrub in this community, an indicator species, is Mountain Mahogany (Cercocarpus montanus) which actually requires a disturbance like fire to reproduce. It does so by root crown sprouting and seed sprouting.

The mix of species varies somewhat on the eastern and western slopes because of variations in the timing and amount of precipitation.