|Ecosystem: Defining Terms|
Over the past 30 or 40 years, ecosystem has been defined in a variety of ways. When we use the term in this article, we mean a system that has a source of energy (the sun) and includes living and nonliving components. The living components include plants and animals, including human beings. The nonliving components include soil, rocks, water, air, and other physical features. Resource managers use a number of concepts when discussing ecosystems. The major ones include scale, connection, change (including both change over time and change over space), diversity, and balance.
|Historic photographs provide a point of comparison with modern conditions and show how ecosystems change over time. These photographs are of the town of Grafton and the Virgin River in southwestern Utah. The first was taken in 1908 and shows a wide shallow river channel with little vegetation. A photograph taken from the same spot in 1993 depicts a narrower river channel with a defined flood plain terrace and heavy streamside vegetation. Cattle grazing in the uplands near the turn of the century may have contributed to loss of vegetation cover and accelerated erosion, which increased the river's sediment load. Today, Grafton is a ghost town.|
Courtesy of the U.S. Geological Survey, Denver, Colorado.
Ecosystems are like communities--they occur at different scales. There are small "communities" such as the living and nonliving components interacting in a pond, and larger communities, such as watersheds. At the global level, all the living and nonliving elements of the planet are interacting. Ecosystems exist wherever plants, animals, and people have an interdependent relationship within the context of their physical environment. For purposes of study we can draw an imaginary circle around communities at different scales to examine the relationships of elements within the circle. When doing this, however, it is important to remember that small ecosystems are nested within larger ecosystems. This means that what happens at one scale affects what happens at every other scale, with varying degrees of impact.
The humans, plants, animals, and other physical elements of an ecosystem are connected in an interdependent web. Ecosystems are connected to one another at various scales. Some of these connections are very complex and difficult to detect or even imagine. For example, scientists have observed a thinning of the ozone layer but have not yet developed a full understanding of all of the contributing causes.
|Cycles and Change|
All materials in an ecosystem cycle and change over time and space. Some changes occur as a result of natural cycles, such as the carbon cycle and the water cycle, or as a result of natural phenomena such as hurricanes, earthquakes, tornadoes, volcanoes, storms, or fires. Humans bring about other changes through migration, urbanization, population expansion, agriculture, industrialization, war, and other interactions with their environment. Changes that occur over long periods of time, such as the adaptation of species, or the drifting of continents, are difficult for humans to perceive.
Biological diversity, or biodiversity, is a key part of healthy ecosystems. It refers to the variety of plants or animals within a single species, the variety of the species themselves, and the variety of ecosystems. Diversity strengthens the potential of populations and species to respond or adapt to changing environmental conditions. Since plant and animal resources provide products and processes important to agriculture, medicine, industry, art, and music, plant and animal diversity also affect human welfare.
In all the Earth's long and varied history, there has never been the massive disappearance of plants and animals that is occurring today. Since the arrival of the Europeans in North America, over 500 animal and plant species have become extinct, while the rate of loss at the demise of the dinosaurs was only one species every 10,000 years. The main reason for this greatly accelerated pace of extinction is habitat loss caused by direct or indirect human interference.
Although constantly cycling and changing, the plants, animals, and other parts of healthy ecosystems are able to regulate themselves to adapt and respond to changes and stresses. Ecosystems at risk or dying have lost this resiliency. Just like a basketball that has lost too much air, they cannot bounce back. By dramatically changing environments in which they live, humans can have a profound effect on the ability of ecosystems to respond to stress. The challenge is to find ways in which human needs can be met without exceeding the natural limits of ecosystems.
|People are an integral part of the Earth's ecosystem and the health of ecosystems is intertwined with the viability of human communities. Like all living beings, people require the use of resources. From the air we breathe, to our food, water, shelter, clothing, arts, and communication networks, we consume resources to live. Just try to imagine something in your home that is not grown or mined. We tend to forget the fact that natural resources usually support a country's economy. Ecosystem management has as its goal the wise and reasonably paced use of these resources to assure their availability far into the future. |
Monitoring And Assessment
Scientific information gathered through inventory, monitoring, and assessment forms the basis of ecosystem management. As you might imagine, tracking and evaluating the effects of multiple actions on something as complex, interactive, and dynamic as an ecosystem is no simple matter. To define even the scale of a particular ecosystem is fraught with controversy--should we look at continents, geographic regions, watersheds, vegetative communities, small study tracts, or soil microbe communities? Scientists have come to realize we need to look at all of them. But how can we spend our time and money collecting appropriate data?
Early miners took canaries into the mines with them because the birds were sensitive to poisonous gasses. These canaries would react before the gasses had a noticeable effect on the miners; they were an early alert to trouble. Occasionally, nature gives us such signals. Examples are the invasion of undesirable weed species when grasslands are overgrazed, and changes in aquatic plant and animal communities in response to pollution. More commonly, however, the signals of ecosystem deterioration are not so easy to read. Choosing the right data to monitor is crucial to whether or not we can detect ecosystem instability.
Once the most useful data has been identified, the next challenge is how to collect and store that information. Data should be collected in a rigorous and consistent manner. Data collection procedures are beginning to be standardized across administrative boundaries, but there is still a long way to go on broad scale efforts, especially international ones.
Some current techniques for collecting monitoring data include laboratory analysis of water, soil, and air samples for contaminants and various life-forms; inventories of plant and animal species; genetic studies; sensors in smokestacks; and satellite sensors. To assess how ecosystems have changed over time, and to track natural cycles that may span centuries, scientists tap historic data, such as old photographs and diaries, and data from archaeological sites. Fossil pollen, present in soil, reveals ancient plant community composition, and even ancient garbage dumps provide surprising clues about the plants and animals that once lived in an area.
Interpreting the collected data is perhaps the most difficult aspect of monitoring. Information from a variety of sources must be synthesized and integrated to paint a complete picture. And, since environmental science is a relatively new endeavor, the implications of certain data are not clear-cut.
Researchers are constantly devising new and better technologies for tracking the condition of the environment. (In fact, this is a fast-growing industry, one with abundant career opportunities.) Ideally, monitoring and assessment give the resource manager or community decision maker constant feedback about the effects of management practices and their relationship to long-term sustainability. This permits adaptive management, or ongoing adjustments, so that "environmental trainwrecks" can be avoided.
The shift to a philosophy of ecosystem management is beginning to result in resource managers actually applying the philosophy in managing the land and resources under their care. These actions can be termed "prevention," "control," or "remediation." Preventive measures avoid damage, threats, or potential conflicts before they happen. Such measures might include planting shade trees and designing visitor centers to work with the daily solar cycle rather than installing standard air-conditioning; designing hiking trails to slow erosion and avoid disturbance to archaeological sites; and eliminating the noxious invader plant knapweed through release of seedhead flies, the larvae of which eat the plant's seeds.
Control measures remove harmful substances before they reach the ecosystem or forestall processes that would cause damage. Actions such as placing "water-bars" (low, angled mounds of soil) across steep dirt roads to reduce erosion and rutting; allowing natural fire cycles to occur; and replanting an erosion-prone burned area with native species are all control measures.
Remediation (also called "restoration") actions lessen the effects of an action that was harmful, or repair and improve a damaged area. For example, new technologies, including the use of certain algae, mitigate the harm oil spills do to biosystems and wildlife; changing livestock grazing patterns can allow damaged riparian (streamside) ecosystems to heal, aided by the use of bank-stabilizing vegetation; and microorganisms and plants that concentrate or isolate heavy metals can restore mine areas to more productive soils.
A Vision for the Future
The goal of ecosystem management is to achieve healthy, productive, and diverse ecosystems as well as healthy human communities--people working in ways that keep the environment healthy and sustainable in perpetuity. This vision of the future involves substantial challenges, and, like all change, may be difficult to accept. Still, nothing short of sustainable ecosystems will guarantee the health of our planet, or the quality of life for future generations.
Another vision for the future would have today's students conversant with the concepts and principles of ecosystem management, so that they can become innovators and sound decision makers. Fortunately, since ecosystems are all around us, students can begin learning right in their own backyard. Also, there are actions and projects children can undertake that will make a real and meaningful difference in ecosystem health.
The advantages of teaching about ecosystems and their wise management are many. For one, the subject encourages students to think about their world holistically and to see connections between parts, both in their study of the natural world and in other intellectual pursuits. Also, teaching ecosystem management enables students to be problem solvers and to respect the different viewpoints any issue engenders. As another advantage, this subject renders many concepts real and concrete rather than abstract and irrelevant, and encourages a child's interest and curiosity. Having real problems to solve and actual cases to observe and manipulate stimulates the desire to learn and participate...and, that, after all, is what it will take to make ecosystem management work.
Humans in the Ecosystem
Historians, archaeologists, and cultural anthropologists routinely gather and interpret data about past environments and the ways humans have altered or been affected by them. Without an understanding of human effects on the environment through time and the long-term natural cycles of change, decisions on how to manage an ecosystem can be subject to error.
Archaeological data can tell us which plants and animals were present at a particular place and time; such data are available for North American cultures for the last 12,000 years. Resource managers rely on this information when planning future plant and animal conditions within a given ecosystem. Archaeologists can also tell us ways in which earlier cultures interacted with their natural environment as well as the outcomes of their approaches to resource management; that kind of information may help us evaluate the consequences of decisions today.
|Anasazi pithouse and roof of masonry building showing prehistoric uses of wood. Roofs of masonry buildings consisted of several layers of large and small timbers laid at right angles to one another.|
Data used to reconstruct prehistoric climates (paleoenvironments) are routinely gathered during archaeological studies. For example, specialists study fossilized pollen found in buried archaeological deposits and in preserved pack rat nests. Each species of plant has a unique pollen, so that the pollen record gives direct evidence about the plants, wild and cultivated, growing in a locality. Pack rats are environment "samplers"; they will gather pieces of most plants growing within 50 meters of their nests. Stored in the nests, and constantly covered with "amberrat" (the pack rat's thick urine), plant parts are preserved; in the arid West, pack rat nests protected in cliffs and rocky overhangs can last thousands of years.
Other tools archaeologists use to reconstruct past climates are tree-ring studies, soils analysis, and geomorphological analyses. Through these studies, information is gleaned on vegetation composition, soil conditions, and drought cycles, data helpful in distinguishing natural from human-induced environmental changes.
Historical records, such as old photographs, survey records and surveyors' notes, and oral histories are invaluable for understanding more recent impacts of humans on the environment. Surveyors' notes record vegetation and animal populations just prior to the period of rapid westward expansion, providing a detailed "snapshot" in time. Similarly, comparisons of photographs taken from the same vantage point decades apart document landscape changes.
Cultural anthropologists record how contemporary and historic Native American cultures have responded to and influenced their natural environments, and the traditional uses they have made of their natural resources and ecosystems. Among other things, such studies have "rediscovered" successful land management practices developed by these cultures over many millennia.
The archaeological record shows us that some of our major contemporary ecosystem issues have a prehistoric parallel; consider the case of the Anasazi people. Wood consumption was extensive in ancient villages; it was used as fuel for heat, cooking and firing of ceramic vessels, and as construction material for structures. The roofs of some large structures required about 160 juniper logs to construct!
Archaeologists hypothesize that sometimes wood resources surrounding agricultural villages were sufficiently decimated as to make the area uninhabitable. What evidence could archaeologists look for to test this hypothesis?
At the Grass Mesa village site in southwestern Colorado, archaeologists found only one type of wood-- juniper--at the level corresponding to the earliest human occupation in about A.D. 800 (see graph). Population at that time is estimated to have been about 10 people. Over the next century, the population increased to 300, then dropped to 10 by the time the site was abandoned in about A.D. 925. Presumably, the earliest occupants could have chosen any local trees they wanted, and those species growing on the mesa would have been the easiest to harvest. At the level of the site representing the period of population growth, archaeologists found wood from at least five species; at the time of population peak, at least 10 tree species were being used. Cottonwood, an inferior construction material that had to be transported from the valley bottom to the site, began to be used for the first time.
In the face of a wood resource shortage, the prehistoric Anasazi had several choices:
- to use less desirable wood species,
- to use less wood,
- to use wood from farther and farther away,
- or to move the village to a new location.
Can you think of other alternatives? Today, in the face of our depleted forest resources, what choices do we have? How do our choices differ from the Anasazi's? The Grass Mesa residents chose to move their village. What can we learn from their experience?
Sound Data for Decisionmakers
Helping to bring about the vision of ecosystem management is a new bureau, the Department of the Interior's (DOI) National Biological Survey (NBS). The NBS consolidates the functions of biological research, inventorying and monitoring, and information transfer across seven DOI bureaus. It will provide the DOI agencies with sound data upon which to base management of the nation's natural resources.
By drawing together in one place the most accurate and current information about biological resources, the NBS will accomplish a number of important goals, including increasing the efficiency of research efforts and expanding the ability to share data. Perhaps most importantly, the NBS will be focusing on the future, identifying potential problems before they become crises. The NBS's mission is to increase our ability to identify well in advance ecosystems that may be at risk, and to provide land managers with relevant information with which to avoid or reduce those risks. The result will be public lands managed for harmonious, long term sustainablity.
|Before and during mining, prevention and control measures can be used to mitigate adverse effects on the environment. Following mining, mined lands can be reclaimed to the original or new uses to return them to a productive state.|
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