Bear River: Last Chance to Change Course

3. From Alpine to Desert: The Changing Ecology of the Bear River Basin

47 From Alpine to Desert: The Changing Ecology of the Bear River Basin As the Bear River Basin scribes its great, five-hundred-mile long looping arc, it passes through a stunning spread of vegetative zones. From alpine to desert the Bear is a major character in nature’s ecological narrative. It remains a story with a biologically diverse cast, but authorship changes from the singular voice of nature to collaboration with human beings. The habitats of the Bear River Basin are in flux. Recent geologic history is playing a slowly evolving role, especially in the aquatic habitats of the lower riverine system and its streamside communities . Human interventions are accelerating changes in the Bear River’s ecology—sometimes passively, sometimes actively. Writing a quickening narrative, human beings are altering the environment in which all plant and animal stakeholders must try to survive. Alpine, subalpine, mountain brush, upland, and desert shrub are the primary life zones characterizing the Bear River Basin, as well as most Intermountain West landscapes. But suggesting these vegetation zones are defined by crisply separated species would underplay the rich biological diversity and create a convenient but artificial portrait. Rather, transitions between each zone are subtle. Sometimes one zone thrives within another, dominant one. That’s because the zones contain varied microenvironments created by intricate interactions of soils, hydrology, elevation, and climate. Something as simple as the land’s angle to the sun can make a dramatic difference. The upper reaches of the Bear River Basin are a classic montane region, marked by alpine, subalpine, and mountain-brush communities of flora and fauna that flourish in a higher, wetter landscape . Typically these life zones lie at elevations from 8,000 to 11,000 feet. But there are no crisp boundaries where a change in altitude slices off one habitat from another. In reality, the mixture of microhabitats is only secondarily defined by elevation. Other factors come into play. For instance, while temperature is a function of elevation, mountains create some anomalies. Depressions like Peter Sink in the Bear River Range can trap cold air in the winter, leading to arcticlike climates with temperatures that can dip to sixty degrees below zero, creating colder habitats than those on higher slopes. Similarly cold air tends to tumble down steep mountain slopes and collect in lower eastern valleys, explaining why Rich County, 3 Chapter 48 Bear River Utah, and Caribou County, Idaho, through which the Bear flows, are often the coldest spots in the lower forty-eight states. Mountains, so characteristic of the Bear River Basin, work with the sun to create wet and dry environments that are only marginally affected by elevation. North- and east-facing aspects of mountains tend to be wetter climates, holding the moisture in their soils longer. These slopes are better habitats for the conifers of the Bear River Basin: subalpine fir, Engelmann spruce, lodgepole pine, and Douglas fir. Depending upon how steep these slopes are and if the surface or groundwater flows are slowed enough, new microhabitats are created for a slightly different mix of montane flora and the insects and animals that rely on these plants. South- and west-facing slopes in the Bear River Basin tend to lose their water faster to the hydrological cycle and have warmer, drier climates over more months than north- and east-facing aspects. That explains why sagebrush, a dominant plant in lower, drier elevations , can extend upward to almost 10,000 feet in the basin. Soils, too, interact with temperature and elevation to create different ecological niches. The highest elevations of the Bear River Basin in the headwaters area, which are characterized by less Tundralike organisms populate the alpine zone: lichens, grasses, forbs, sedges, and low-lying shrubs. Ranging widely through various elevations along riparian corridors in the basin, moose leave their calling cards. 49 From Alpine to Desert oxygen, longer winters, biting winds, and poor, rocky, shallow soil, support only tundralike organisms: lichens, grasses, forbs, sedges, and low-lying shrubs. Lower in the basin, in the bottomlands or riparian areas close to the Bear River, soils change from the metamorphic and igneous rocks of the headwaters to weathered shale and sandstone. Moreover, the fine silts and clays left over from Lake Bonneville are relatively deep, retain water much longer, and tend to be moderately saline and strongly alkaline. The montane habitats of the Bear River Basin also contain numerous high-mountain wetlands. These...