Mountains and Plains

The Ecology of Wyoming Landscapes

Yale UNIVERSITY PRESS

Contents

Introduction

Straddling the Continental Divide and with an average elevation of 6,700 feet above sea level, the landscapes of Wyoming are similar to those encountered by explorers in the early 1800s. There are now roads, ranches, farms, cities, and industrial developments, but outdoor enthusiasts, naturalists, and scientists are attracted by the wildlife and natural ecosystems that still exist over large areas. The persistence of such amenities can be attributed to a cool climate, rugged terrain, and extraordinary features that are highly valued. Yellowstone National Park was established in 1872—the world's first national park. Nineteen years later, in 1891, a forest reserve was established nearby. It became the Shoshone National Forest. In 1906 the nation's first national monument was established at Devils Tower in northeastern Wyoming, and Grand Teton National Park was established in 1929. Since then fifteen wildlands in Wyoming have been designated Wilderness by Congress. National parks, wilderness, and wilderness study areas account for about 9 percent of the state's land (figs. 1.1–1.5).

In addition, native prairie and shrublands persist in some areas, primarily because 37 percent of the state is above 7,000 feet elevation, where growing seasons are too short and cool for cropland agriculture. At lower elevations water is more likely the limiting factor, with most agriculture requiring irrigation. Farmers tried various crops in the late 1800s, but their fields commonly failed. The federal government purchased abandoned homesteads in the late 1930s, and some became national grasslands—the Thunder Basin National Grassland in northeastern Wyoming and the Pawnee National Grassland in northern Colorado. Only about 4 percent of Wyoming is currently under cultivation, leaving large tracts of land that have never been plowed and are still dominated by native plants. Overall, the most significant landscape changes have occurred in three settings: (1) along rivers at low elevations, where irrigation water is available and people enjoy having their homes; (2) in the foothills, where many homes have been constructed and fires have been suppressed; and (3) where the extraction of energy resources is feasible.

During the past 20 years, Wyoming and adjacent states have experienced surprisingly rapid changes. Still, there are many opportunities for learning about the natural history of the Rocky Mountains and western Great Plains. Bison have been replaced in most areas by cattle, but pronghorn, elk, and deer are still common. Livestock have grazed some rangelands heavily, but bison may have done the same. Grizzly bears, elk, and wolves no longer wander across the basins and plains to the extent they once did, but all are found in some areas. Roads, timber harvesting, and industrial developments have fragmented mountain forests and basin shrublands, but not everywhere. The question is: How can the land be managed so that highly valued natural resources are used wisely during a time of alarming rates of habitat degradation and climate change? The sciences of ecology and conservation biology are pertinent to answering this question.

Ecology

Most ecologists would argue that it is important to protect air and water quality, conserve biological diversity, and maintain soil productivity. Yet advocacy for environmental protection is not ecology per se. Rather, ecology is a science dedicated to understanding the interactions among plants, animals, microorganisms, humans, and their environment. The interactions are studied to be understood, not to be judged as good or bad. Ecologists strive to be objective through systematic measurements, experimentation, and analysis. Many also work to ensure that decisionmakers are provided with the best ecological information available.

The goal of modern ecological research, as in other sciences, is to understand patterns and processes in nature well enough to make predictions. This includes anticipating the effects of environmental changes on the distribution and population sizes of all kinds of life, and on the movement of water, nutrients, and energy. Theoretical ecologists search for generalizations that apply everywhere. Others are empirical; that is, they focus on specific areas and address interactions associated with, for example, specific tracts of forests and rangelands. Each approach is beneficial for the other.

Modern ecology can be divided into numerous sub-disciplines. To illustrate, physiological ecologists work to understand how organisms are adapted to their environment, whereas population ecologists seek to understand why population sizes fluctuate through time and vary from place to place. Community ecologists focus on the interactions among coexisting species in a specific area—the community. Others study ecosystems, defined as areas where plants, animals, and microbial organisms interact with one another and their environment. Ecosystem ecologists commonly measure flows of energy, water, and nutrients through the soil, atmosphere, detritus, and living organisms (fig. 1.6). Often the innumerable species are grouped into green plants (the producers) that convert the energy of sunlight into new plant material, herbivores that eat plants, carnivores that consume other animals, omnivores that depend on both food sources, and detritivores and decomposers that derive their energy and nutrients from dead plants and animals. As the populations of a community or ecosystem change, other attributes change as well (for example, rates of streamflow, photosynthesis, herbivory, and the cycling of nutrients). Of interest to many ecologists is how the abundance of different species and their influences are affected by varying environmental conditions, and how they change with time following disturbances. Some ecologists specialize in the study of plants, whereas others concentrate on bacteria, fungi, insects, birds, mammals, or other organisms.

Another branch of ecology is landscape ecology. Ecologists working at this scale commonly focus on large heterogeneous areas, for example, square miles of grasslands and shrublands. They are curious about how the landscape has changed in recent decades or centuries, and how it might change in the future. Another goal is to determine the causes and effects of different landscape patterns. Aerial photographs, satellite images, and maps are important tools for their work. The terms landscape and ecosystem are sometimes used interchangeably. To illustrate, the Yellowstone landscape made famous by the artist Thomas Moran in the 1870s is a mosaic of communities and is now often referred to as the Greater Yellowstone Ecosystem (see chapter 15). The boundaries of an ecosystem or landscape are established according to the objectives of a study or management challenge. The area included may be as small as a pond or as large as several counties or states, or even continents.

Ecology is a diverse science that fosters an improved understanding of all the various forms of life in an area and the ecosystems they inhabit. To facilitate ecologists' work, diagrams are drawn to illustrate the plethora of possible interactions, such as those illustrated in fig. 1.6. Some of the drawings are similar to those prepared by engineers, but there is a significant difference—natural ecosystems were not designed and constructed by humankind. Rather, they emerged after millions of years of evolution and centuries of ecosystem development. Much remains to be learned about the species and processes that enable their long-term persistence.

Conservation Biology

As for ecologists, conservation biologists can take several approaches to their research. In general, they are experts on rarity and what, if anything, can be done about it. Some species are rare because their habitat has been degraded by human activity; others are naturally rare and are found only in one or a few small areas. Ultimately, conservation biologists work to facilitate sound management programs that lead to the maintenance or recovery of threatened species, thereby reducing the need for the strict mandates of the Endangered Species Act. In Wyoming, seven plants, six mammals, six birds, six fish, and one amphibian are currently protected by federal law or are under consideration for protection (figs. 1.7–1.9). Others are of special interest because they are endemics, that is, they are found nowhere else. Such species—along with those that are common and widespread, and all the varieties in each species—compose the biological diversity of an area.

The conservation of rare and endangered species requires information gained by scientists in ecology as well as other disciplines. More specifically, biologists with expertise in evolution and species identification are needed to verify that so-called rare species are verifiable species and are indeed rare. Some of them are difficult to distinguish from related species that are common, which leads to controversy about whether the restrictions of the Endangered Species Act are needed. Do the advocates of such action really know? The expertise of systematists, taxonomists, and geneticists is required. It's clear, however, that scientists cannot accomplish the goal of conservation by themselves. Stemming the tide of habitat destruction and extinction requires joining forces with people from all walks of life—landowners; policymakers; nongovernmental organizations; and local, state, and federal agencies. Collaborating with so many parties is complicated but necessary as increased value is placed on rare species and other limited resources. Notably, some resources, though not traditional commodities, have the potential of providing ecosystem services that can be bought and sold.

Ecosystem Services

Earth's ecosystems provide many benefits in addition to habitat for wildlife and rare species. These benefits, often referred to as ecosystem services, include

• erosion control,

• maintenance of soil fertility,

• inhibition of invasive plants,

• provision of clean water,

• air filtration,

• mitigation of droughts and floods,

• provision of habitat for insects that pollinate crops,

• detoxification and decomposition of waste materials,

• sequestration of carbon dioxide,

• control of agricultural pests, and

• provision of meat from areas that are too dry to cultivate using standard agricultural practices.

Such benefits are provided by the diversity of native plants, animals, and microbes that thrive in the harsh environments of the region.

Ecosystem services generally have been undervalued or overlooked, leading to inevitable and undesirable consequences. Their value becomes clear when the costs are summed for the time, labor, and energy required for water purification, herbicides, insecticides, fertilizer, and the control of soil erosion. When economists calculate all the costs of replacing such services with modern technology, much of which requires the burning of fossil fuels, the value of ecosystem services is estimated at trillions of dollars per year. The Farm Bill of 2008, passed by Congress, called for measuring the environmental benefits gained from managing farm and ranch lands more carefully.

Considering their value, it should not be surprising that some ecological services now can be bought and sold, thereby creating opportunities for landowners, businesses, consumers, and governments to become more directly involved with supporting sustainable resource management. An example is the buying and selling of carbon credits as a means of reducing carbon dioxide emissions to the atmosphere, a major contributor to global climate change. Similarly, the Conservation Reserve Program of the U.S. Department of Agriculture provides monetary incentives for farmers to establish perennial plant cover on erodible land, thereby enabling carbon sequestration as well as soil stabilization and water purification—powered by solar energy rather than fossil fuels. Other examples are discussed in chapter 18.

In sum, whereas ecologists study adaptations, populations, communities, and ecosystems, conservation biologists strive to develop strategies for conserving our evolutionary heritage. And now, a newly emerging multidisciplinary group of professionals seeks to identify and profit from investments in maintaining ecosystem services.

Landscape History

Millions of Years Ago

Rocks exposed in canyons, escarpments, and mountains provide the data geologists need to interpret the development of western landscapes. Unimaginable changes have occurred. About 350 million years ago, during the Paleozoic Era (fig. 2.1), the area that would become Wyoming was covered by seawater and the climate was tropical. The water receded and advanced many times, depositing sand in some places and more finely textured silt and clay elsewhere. Sandstones, siltstones, claystones, and other kinds of sedimentary rock were formed. Skeletal fragments from coral and other marine organisms, rich in calcium carbonate, became limestones. An example is the Madison Limestone that forms many escarpments in the region today.

Also during the Paleozoic, shifting seas created enormous swamps and tidal flats that were frequented by dragonflies with 30-inch wingspans. Primitive vascular plants were abundant, including tree-sized clubmosses, ferns, and horsetails. Fossilization was less frequent on the uplands, but there were woodlands that included primitive gymnosperms, such as the ancestors of cycads, ginkgo, pine, spruce, fir, and sequoia. Mountain ranges were uplifted and essentially leveled by erosion within tens of millions of years.

By the early Mesozoic Era, about 240 million years ago, most of Wyoming was slightly above sea level—and still near the equator (fig. 2.2). Fluctuating coastal environments in the Triassic Period led to formation of the colorful sandstones and shales of the Chugwater and Spearfish formations, both rich in iron oxides and known as redbeds. Subsequently, in the Jurassic Period, extensive sand dunes were consolidated into the Nugget Sandstone. Various episodes of volcanism occurred toward the end of the Mesozoic, during the Cretaceous Period, leaving deposits of fine ash across the landscape and in the sea. Much of this ash became bentonite, a sodium-rich clay of considerable economic and ecological importance.

Also during the Cretaceous, thrust faulting created the Hoback, Salt River, Sublette, and Wyoming mountain ranges, now located near the Wyoming-Idaho border. These mountains, known collectively as the Overthrust Belt and now an important source of oil and gas, are composed of sedimentary rock. Another round of mountain building began about 75 million years ago, during the late Cretaceous, with folding and faulting of Earth's crust throughout the region. For about 30 million years, Precambrian granite and other igneous and metamorphic rocks, together with overlying sedimentary strata, were thrust upward. This period of mountain building is known worldwide as the Laramide orogeny. The overlying Paleozoic and Mesozoic sedimentary strata gradually were eroded from the older rocks and washed into the newly defined intermountain basins.

The Mesozoic would have been especially exciting for biologists, as dinosaurs were abundant in the still-tropical climate. About forty different kinds are recognized in the fossil record from Wyoming alone. Some were huge, suggesting that the vegetation was abundant enough to provide large amounts of food. Others were small, less than a few feet long. These reptiles, along with other nondinosaurian reptiles like the flying pterosaurs, were important residents of Earth for more than 100 million years. Fossils of some of the most famous dinosaurs have been found at Como Bluff, between the towns of Medicine Bow and Rock River. They include Diplodocus, Apatosaurus, Stegosaurus, Allosaurus, and Dryosaurus. Bison, pronghorn, and other familiar mammals would not be present for another 200 million years.