Aspen Woodlands

Example of the Aspen Woodlands Strategy Habitat, within Fremont-Winema National Forest, Oregon
The fall color of Aspen Woodlands near Rocky Point, within the Fremont-Winema National Forest. Photo Credit: USFS

Aspen woodlands are woodland or forest communities, dominated by aspen trees with a forb, grass, or shrub understory. Aspen woodlands can also occur within conifer forests.

Ecoregions

Aspen woodlands are a Strategy Habitat in the Northern Basin and Range, Blue Mountains, and East Cascades ecoregions.

Characteristics

In open sagebrush habitat, aspen forms woodland or forest communities, dominated by aspen trees with a forb, grass, or shrub understory. In forested mountain habitats, aspen can occur within conifer forests. Aspen primarily occur in riparian areas or in moist microsites within drier landscapes. Characteristic understory grasses include Idaho fescue, pinegrass, Great Basin wildrye, or blue wildrye, and shrubs include sagebrush, snowberry, serviceberry, and roses. Aspen habitats evolved in areas that historically experienced fire. Given sufficient moisture and light, aspen will sprout annually, and they will sprout more vigorously after fire. Without fire disturbance, aspen stands decrease in size (total acres covered) and may be lost to competition from conifer trees. Aspen do not occur in the hottest, driest portions of the Northern Basin and Range ecoregion.

Conservation Overview

Aspen is on the edge of its range in Oregon and is more common further east in the Rocky Mountains and north into Canada. One of the few deciduous trees in eastern Oregon, aspen is especially important in the Northern Basin and Range and Blue Mountains ecoregions. In a landscape dominated by shrubs and grasses, aspen provide additional structure useful as nest sites and hiding cover for wildlife. Aspen stands generally have high invertebrate prey diversity and densities. Aspen is important for birds in both migration and breeding seasons. It also provides fawning and calving habitat, hiding cover, and forage for mule deer and elk. Other wildlife that use aspen include black bear, beaver, rabbits, grouse, and bats. Tree Swallows, woodpeckers, and other birds nest in aspen cavities. Aspen stands contribute to watershed health by serving as snowdrift banks.

Throughout the west, there is concern about the loss of aspen habitats and the lack of aspen regeneration in remnant stands. In the Northern Basin and Range ecoregion, approximately 79 percent of aspen woodlands have been lost since the 1800s. Aspen stands often depend on natural fire to reduce competition from conifers and stimulate the growth of suckers from roots. Chronic overgrazing can prevent overstory recruitment, allow invasive plant species to take hold, and degrade understories. Within a stand, the aspen trees reproduce vegetatively, producing clonal root sprouts arising from a parental root system. While the aspen clone or genet may last for thousands of years, individual trees may only live for 100-150 years. Many existing trees are reaching the end of their natural life cycle, and without young aspen trees to replace them, the stands will be lost completely.

Limiting Factors and Recommended Approaches

Limiting Factor: Altered Fire Regimes and Encroachment From Juniper and Conifers

Fire suppression has resulted in juniper encroachment and lack of reproduction in aspen.

Recommended Approach

Carefully reintroduce natural fire regimes using site-appropriate prescriptions, accounting for the area size and vegetation characteristics that affect resiliency and resistance to disturbance. Use mechanical treatment methods (e.g., chipping, cutting for firewood) to control encroaching junipers, recognizing that reintroducing a disturbance regime may be necessary to reinvigorate aspen reproduction. Apply treatments appropriately with respect to season and location.

Limiting Factor: Lack of Reproduction

In addition to fire suppression, overgrazing has limited aspen recruitment. When conditions are over-grazed, aspen will sprout but not grow fully into trees. Cattle and ungulates impact the soil, herbaceous layer, and sprouts.

Recommended Approach

Limit over-grazing. Use temporary ungulate exclosures to encourage reproduction at high priority sites.

Limiting Factor: Degraded Understories

Invasive plants, introduction of non-native pasture grasses, and historical overgrazing have altered the understory of many aspen stands.

Recommended Approach

Control invasive plants using site-appropriate methods and reintroduce native bunchgrasses and flowering plants at priority restoration sites.

Limiting Factor: Fragmentation

While some aspen patches naturally occurred in isolated patches, habitat conversion has increased fragmentation and isolation of aspen.

Recommended Approach

Analyze historical and current aspen distribution at the watershed scale to plan restoration activities that increase connectivity of aspen patches.

Limiting Factor: Mapping Limitations

Current mapping efforts do not adequately document aspen stands due to their small patch size. Lack of adequate maps affects ability to understand size, extent, and spatial placement of aspen, and to restore connectivity of aspen patches at a landscape scale.

Recommended Approach

Support efforts to map aspen and other important habitats at fine (less than 100 feet pixel) scales.

Resources for more information

  • Oregon State University. 2010. Land Manager’s Guide to Aspen Management in Oregon.
  • Earnst, S.L., D.S. Dobkin, and J.A. Ballard. 2012. Changes in avian and plant communities of aspen woodlands over 12 years after livestock removal in the northwestern Great Basin. Conservation Biology 26:862-872.
  • Bates, J.D. and R.F. Miller. Restoration of aspen woodland invaded by western juniper: applications of partial cutting and prescribed fire. 16th International Conference, Society for Ecological Restoration.
  • Bates, J.D., R.F. Miller, and K.W. Davies. 2006. Restoration of quaking aspen woodlands invaded by western juniper. Rangeland Ecology & Management 59(1):88-97.