Common (Translated Scientific) Name: Narrowleaf Cottonwood - Rocky Mountain Juniper Riparian Woodland

Colloquial Name: No Data Available

Hierarchy Level:  Association

Type Concept: This semi-riparian woodland association occurs in north-central Wyoming, western Colorado and northern New Mexico on terraces or slopes of gorges, ravines, and moderate-sized intermittent or perennial drainages between 1740 and 2400 m (5725-7875 feet) elevation. This type usually occurs on high, dry stream terraces with level slopes and a sandy surface soil texture. Stands are infrequently flooded (10- to 100-year recurrence intervals). The vegetation is characterized by moderately open canopies (25-60% cover) dominated by Populus angustifolia, with Juniperus scopulorum or occasionally Juniperus monosperma, Betula occidentalis, or Pinus edulis in the subcanopy. An open grassy understory with abundant Sporobolus cryptandrus is characteristic, although other grasses such as Carex geyeri, Juncus arcticus ssp. littoralis, Leymus cinereus, and Poa fendleriana may also be present. In disturbed stands the native grasses may have been replaced by exotic species such as Bromus inermis. Although shrubs are uncommon, those present, such as Brickellia californica, Quercus gambelii, Artemisia tridentata, Mahonia repens, Purshia tridentata, Rosa woodsii, and Symphoricarpos oreophilus, reflect relatively dry site conditions. The herbaceous understory also reflects open, dry site conditions. Facultative and upland forbs such as Thalictrum fendleri, Achillea millefolium, Maianthemum stellatum, Solidago nemoralis, and Penstemon barbatus are common. In open areas Bouteloua curtipendula is common. Regardless of the drier conditions, a variety of native wetland indicators can occur, including Juncus effusus, Glyceria striata, Carex nebrascensis, Agrostis exarata, Rudbeckia laciniata, Equisetum arvense, Epilobium ciliatum, Mertensia ciliata, and Equisetum laevigatum. Many stands have decadent Populus angustifolia trees that are being replaced by Juniperus scopulorum. Other stands periodically flood and retain a large amount of woody debris. In all cases the vegetation and topographic position indicate a community that is becoming isolated from the water table. As the water table drops, the facultative and obligate wetland plants will be replaced by upland species.

Diagnostic Characteristics: No Data Available

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: These mature riparian forests occupy some of the driest sites in the floodplain. Some stands may be directly adjacent to the stream but still situated several meters above it due to downcut streambanks, or they may be dry because the stream only flows intermittently. In these stands, the cottonwoods have limited self-sustaining capabilities except vegetatively by root sprouts. Many of the trees are often decadent or dying, and junipers are commonly growing up under them, colonizing the drying terraces. Further, the presence of juniper in these and other floodplain communities is often considered invasive. Juniper, as a codominant in these communities, is at least viewed as an indicator that flooding occurs infrequently. Only the largest of floods will remove these communities.

This type is a refinement of the Populus angustifolia / Juniperus scopulorum Association reported by Muldavin (1991) for northern New Mexico and Kittel et al. (1994, 1996) for Colorado. It is synonymous with Populus angustifolia / Physocarpus monogynus - Padus virginiana in Bighorn National Forest, Wyoming (Girard et al. 1997), and Populus angustifolia - Juniperus scopulorum in New Mexico (Durkin et al. 1995a). Padus virginiana is an old name for Prunus virginiana.

Similar NVC Types: No Data Available

note: No Data Available