Images of Aspen Ecology

Fire on north slope of the Uinta Mountains burned until it ran into pure aspen stands. Fuel moisture in these stands was high enough to stop the fire from burning.

Livestock grazing in the western United States has had an impact of aspen (Populus tremuloides) ecosystems.  Many of these impacts date back to the late 1800's and early 1900's when livestock numbers increased significantly in the West (see table below).  In Utah alone, cattle numbers increased from 39,180 in 1870 to 356,621 in 1900.  More significant, perhaps, is the increase of sheep number from 59,672 in 1870 to over 3.8 million 30 years later in 1900. These numbers of generally unregulated sheep and cattle grazing across our landscapes had devastating effects that are still evident today. Along with the loss of more palatable grazing species, soil loss in some areas contributed to a change in the physical potential of areas to support the kinds of vegetation that once existed.

Cattle and Sheep populations of Idaho, Nevada, Utah and Wyoming, 1870-1900

State	1870	1880	1890	1900
Idaho
Cattle	10,456	84,867	219,431	369,217
Sheep	1,021	27,326	357,712	3,122,576
Nevada
Cattle	31,516	172,221	210,900	386,249
Sheep	21,018	133,695	273,469	887,110
Utah
Cattle	39,180	95,416	200,264	356,621
Sheep	59,672	233,122	1,014,176	3,821,838
Wyoming
Cattle	31,130	278,073	685,956	689,970
Sheep	6,409	140,255	712,520	5,099,765

Source: U.S. Bureau of the Census, 1890 Census of Agriculture, 1:100, and 109; 1900 Census of Agriculture, 2 vols. 1:318 and 320. These are census figures that include all animals in the state.

Aspen stand in the Bear River Range was historically grazed to the point that understory vegetation was almost completely removed. Following understory removal, gophers constantly churn the soil in search of forage underground.

Aspen stand with an understory of aspen bluebells (Mertensia arizonica) illustrates how less palatable species, such as this, become dominant following years of grazing.

Aspen community in grazing allotment with an understory that includes scattered Mountain Brome (Bromus carinatus), Sawleaf Groundsel (Senecio serra), and abundant annuals forbs.

Aspen community in the Mueggler-Butler Fork Research Natural Area at potential with a diverse understory dominated by Cow Parsnip (Heracleum maximum), Valerian (Valeriana edulis), Ligusticum (Ligusticum filicinum), Western sweetroot (Osmorhiza occidentalis), with scattered Monkshood (Aconitum columbianum), Western Coneflower (Rudbeckia occidentalis), and other native perennial forbs and grasses.

Ungrazed Aspen/Tall Forb Community Type in the Walter F Mueggler-Butler Fork Research Natural Area can be used to compare with similar grazed stands to help determine and quantify conditions