Holt environmental science chapter 10 review answers

Chapter 10: Ecological Restoration

10.1 What Is Ecological restoration?

Ecological restoration is defined as providing assistance to the recovery of an ecosystem that has been degraded, dam- aged, or destroyed.2 Originally until near the end of the 20th century, restoration seemed simple: Just remove all human actions and let nature take care of itself. But this led to surprising and undesirable results. A classic example is the conservation of Hutcheson Memorial Forest, the last remaining known uncut, therefore primeval, forest in New Jersey. This forest has been owned since 1701 by the Met- tler family, who farmed and kept this forest as a woodlot that they never harvested, as careful family records showed. In 1954, Rutgers University obtained the forest, and ecolo- gist Murray Buell, who arranged for the purchase, planned that it would be left undisturbed and therefore would rep- resent an old-growth oak-hickory forest, the kind that was supposed to be the final endpoint of forest succession (see Chapter 6 for a discussion of succession).

What was this forest supposed to be like? In 1749 to 1750, the Swedish botanist Peter Kalm traveled from Philadelphia to Montreal, collecting plants for Carl Lin- naeus. Kalm traveled through this area of New Jersey and described the forests as being composed of large oaks, hickories, and chestnuts, so free of underbrush that one could drive a horse and carriage through the woods.3

An article in Audubon in 1954 described this wood as “a climax forest . . . a cross-section of nature in equilibrium in which the forest trees have developed over a long pe- riod of time. The present oaks and other hardwood trees have succeeded other types of trees that went before them. Now these trees, after reaching old age, die and return their substance to the soil and help their replacements to sturdy growth and ripe old age in turn.”4 But this was not how the forest looked in the 1950s nor how it looks today (Figure 10.4). There are some old trees, many of them in poor condition, and the forest is dense with young tree stems of many sizes. Few oaks have regenerated. In the 1960s, the majority of the seedlings in the forest were maples.

What went wrong? Reconstruction of the forest his- tory showed that prior to 1701 when Europeans took over the land, the Indians had burned this forest on average every ten years. These frequent light fires keep the land relatively open and supported oaks and hickories, resistant to fire, and suppressed maples, easily killed by fire.

These findings created a dilemma. The nature pre- serve was set up to provide an example of the way the forests were before European alternation of the land, and therefore would never be subjected to cutting, planting, fires, or any other human action. But the forest wasn’t like that at all. What should be done? Should it be left alone to become whatever it would, probably a forest nobody had ever seen and really didn’t want? Or should it be manipu- lated to make it look like the forests of the 18th century? It is a puzzle. The forest management has basically ignored the question since Murray Buell’s time, but the default is following the first option.

The story of Hutcheson Memorial Forest makes clear that restoration cannot mean a return to some imaginary past single original state, nor can it mean management with no actions. This is a hard lesson to learn, and it con- tinues to be violated. But the best of modern ecological restoration takes this into account.

Today, a distinction is made between restoration ecol- ogy and ecological restoration. Restoration ecology is the science of restoration; ecological restoration is the appli- cation—the actual activity of restoring ecosystems. Some general principles for restoration are:

• Ecosystems are dynamic, not static (change and natural disturbance are expected).

• No simple set of rules will be applicable to a specific restoration project.

• Adaptive management, using the best science, is neces-

sary for restoration to succeed.

• Careful consideration of ecosystems (life), geology (rocks, soils), and hydrology (water) plays an important role in all restoration projects.

Of particular importance is the principle that ecosystems are dynamic, not static—that is, they are always changing and subject to natural disturbance. Any restoration plan must consider disturbance and how resilient the restored system will be. Also important is adaptive management, the application of science to the management process. Hy- potheses may be tested, and, as restoration goes forward, flexible plans may be developed to accommodate change. Probably the most common projects involve river restora- tion and the restoration of freshwater and coastal wetlands.5

There is also ecological engineering, which is defined as the design of ecosystems for the mutual benefit of hu- mans and nature. It is a multidisciplinary activity involving habitat reconstruction; stream and river restoration; wet- land restoration and construction; pollution control by eco- systems; and development of sustainable agro-ecosystems.

10.2 goals of restoration: What Is “Natural”?

If an ecosystem passes naturally through many different states and all of them are “natural,” and if the change it- self, caused by wildfire, flood, and windstorm, is natural, then what is its natural state? And how can restoration that involves such disturbance occur without damage to human life and property? Can we restore an ecological system to any one of its past states and claim that this is natural and successful restoration?

In Chapters 4 and 6, we discussed the ideas of steady- state and non–steady-state ecological systems. We argued that until the second half of the 20th century the predom- inant belief in Western civilization was that any natural area—a forest, a prairie, an intertidal zone—left undis- turbed by people achieved a single condition that would persist indefinitely, just as was assumed for the Hutcheson Memorial Forest. This condition, as mentioned in Chap- ter 4, has been known as the balance of nature. The major tenets of a belief in the balance of nature are as follows:

• Left undisturbed, nature achieves a permanency of form and structure that persists indefinitely.

• If it is disturbed and the disturbance is removed, nature returns to exactly the same permanent state.

• In this permanent state of nature, there is a “great chain of being,” with a place for each creature (a habitat and a niche) and each creature in its appropriate place.

Attempts to save nature following these beliefs are called preservation. These ideas have their roots in Greek and Roman philosophies about nature, but they have played an important role in modern environmentalism as well. In the early 20th century, ecologists formalized the belief in the balance of nature. At that time, people thought that wildfires were always detrimental to wildlife, vegetation, and natural ecosystems. Bambi, a 1942 Walt Disney movie, expressed this belief, depicting a fire that brought death to friendly animals. In the United States, Smokey Bear is a well-known symbol used for many de- cades by the U.S. Forest Service to warn visitors to be careful with fire and avoid setting wildfires. The mes- sage is that wildfires are always harmful to wildlife and ecosystems.

All of this suggests a belief that the balance of nature exists. But if that were true, the answer to the question “restore to what?” would be simple: restore to the original, natural, permanent condition. The way to do it would be simple, too: Get out of the way and let nature take its course. Since the second half of the 20th century, though, ecologists have learned that nature is not constant, and that forests, prairies—all ecosystems—undergo change. But sometimes, in subtle ways, there is a retreat to the bal- ance of nature idea. For example, a scientific paper pub- lished in 2009 suggested that carbon storage by forests could be based on the amount stored in old growth.6,4 The assumption is that forests, left to grow without human interference, will “restore” themselves to a single biomass and therefore carbon storage, and will remain there for- ever. This is a balance of nature assumption.

Change has been a part of natural ecological systems for millions of years, and many species have adapted to change. Indeed, many require specific kinds of change in order to survive. This means that we can restore ecosystem processes (flows of energy, cycling of chemical elements) and help populations of endangered and threatened spe- cies increase on average, but the abundances of species and conditions of ecosystems will change over time as they are subjected to internal and external changes, and following the process of succession discussed in Chapter 6.

Dealing with change—natural and human induced— poses questions of human values as well as science. This is illustrated by wildfires in forests, grasslands, and shrub- lands, which can be extremely destructive to human life and property. From 1990 to 2009, three wildfires that started in chaparral shrubland in Santa Barbara, Califor- nia, burned about 1,000 homes. The wildfire hazard can be minimized but not eliminated. Scientific understand- ing tells us that fires are natural and that some species re- quire them. But whether we choose to allow fires to burn, or even light fires ourselves, is a matter of values. Restora- tion ecology depends on science to discover what used to be, what is possible, what an ecosystem or species requires to persist, and how different goals can be achieved. But selecting goals for restoration is a matter of human values. Some possible goals of restoration are listed in Table 10.1. Which state we attempt to restore a landscape to (preindustrial to modern) depends on more-specific goals and possibilities that, again, are linked to values. For example, restoring the Florida Everglades to a preindustrial state is not possible or desirable (a value), given the present land and water use that supports the people of Florida. The goal instead is to improve biodiversity, water flow through the Everglades, and water quality (see opening Case Study).

10.3 What Is Usually restored?

Ecosystems of all types have undergone degradation and need restoration. However, certain kinds of ecosystems have undergone especially widespread loss and degrada- tion and are therefore a focus of attention today. Table 10.2 gives examples of ecosystems that are commonly restored.

Attention has focused on forests, wetlands, and grass- lands, especially the North American prairie; streams and rivers and the riparian zones alongside them; lakes; beach- es; and habitats of threatened and endangered species. Also included are areas that people desire to restore for aesthetic and moral reasons, showing once again that restoration in- volves values. In this section, we briefly discuss the restora- tion of rivers and streams, wetlands, and prairies.

Rivers, Streams, and Wetlands Restoration: Some Examples

Rivers and streams and wetlands probably are restored more frequently than any other systems. Thousands of streams have been degraded by urbanization, agriculture, timber harvesting, and channelization (shortening, wid- ening, and even paving over or confining the channel to culverts). In North America, large areas of both freshwater and coastal wetlands have been greatly altered during the past 200 years. It is estimated that California, for example, has lost more than 90% of its wetlands, both freshwater and coastal, and that the total wetland loss for the United States is about 50%. Not only the United States has suf- fered; wetlands around the world are affected.

Rivers and Streams

One of the largest and most expensive restoration projects in the United States is the restoration of the Kis- simmee River in Florida. This river was channelized, or straightened, by the U.S. Army Corps of Engineers to provide ship passage through Florida. Although the river and its adjacent ecosystems were greatly altered, shipping never developed, and now several hundred million dollars must be spent to put the river back as it was before. The task includes restoring the meandering flow of the river and replacing the soil layers in the order in which they had lain on the bottom of the river prior to channelization.7

The Kissimmee, which originally meandered 103 miles in central Florida, had an unusual hydrology because it in- undated its floodplain for prolonged periods (Figure 10.5a). The floodplain and river supported a biologically diverse ecosystem, including wetland plants; 38 species of wading birds and waterfowl; fish; and other wildlife. Few people lived in the Kissimmee basin before about 1940, and the land use was mostly agricultural. Due to rapid development and growth and a growing flood hazard as a result of in- appropriate land use, people asked the federal government to design a flood-control plan for southern Florida. The channelization of the Kissimmee River occurred between 1962 and 1971 as part of the flood-control plan. About two-thirds of the floodplain was drained, and a straight canal was excavated (Figure 10.5b). Turning the meander- ing river into a straight canal degraded the river ecosystem and greatly reduced the wetlands and populations of birds, mammals, and fish. The Florida Audubon Society estimates that ducks using the river decreased by 93%.8

Criticism of the loss of the river ecosystem went on for years, finally leading to the current restoration efforts. The purpose of the restoration is to return part of the river to its historical meandering riverbed and wide floodplain. Specif- ics of the restoration plan (shown in Figure 10.6) include restoring as much as possible of the historical biodiversity and ecosystem function; recreating patterns of wetland plant communities as they existed before channelization; reestablishing prolonged flooding of the floodplain; and re- creating a river floodplain environment and connection to the main river similar to the way it used to be.7

The restoration project was authorized by the U.S. Con- gress in 1992, in partnership with the South Florida Water Management District and the U.S. Army Corps of Engineers. It is an ongoing project, and by 2012 approximately 23 km of the nearly straight channel had been restored to a mean- dering channel with floodplain wetlands about 24 km long. As a result, water again flowed through a meandering chan- nel and onto the floodplain, wetland vegetation was reestab- lished, and birds and other wildlife returned. The potential flood hazard is being addressed. Some of the structures that control flooding will be removed, and others will be main- tained. Flood protection is a main reason the entire river will not be returned to what it was before channelization.

The cost of the restoration of the Kissimmee River is several times greater than it was to channelize it. Thus, the decision to go forward with the restoration reflects the high value that people in south Florida place on conserving bio- logical diversity and providing for recreational activities in a more natural environment.

Yellowstone National Park is another interesting case. Here, an unanticipated stream restoration has taken place, resulting from the reintroduction of wolves. Wolves were eliminated from Yel- lowstone by the 1920s and were introduced back into the park in 1995–1996. Initially, 66 wolves were introduced, and by 2007 the wolf population had grown to 1,774, with about 98 in Yellowstone itself (Figure 10.7), 736 in Idaho (outside the park), 328 in Wyoming, 653 in Montana, and the rest in other areas.9

Mountain streams in Yellowstone general- ly consist of stream channels, beds, and banks composed of silt, sand, gravel, and bedrock. Cool, clean water is supplied via the hydrolog- ic and geologic system from snowmelt and rain that infiltrate the rocks and soil to seep into streams. The water supports life in the stream, including fish and other organisms, as well as streamside vegetation adjacent to stream chan- nels. The riparian vegetation is very different from vegetation on adjacent uplands. Stream bank vegetation helps retard erosion of the banks and thus the amount of sediment that enters the stream.

Riparian vegetation, such as cottonwood and willow trees, is a popular food source for animals, including elk. Extensive browsing dra- matically reduces the abundance of riparian plants, damaging the stream environment by reducing shade and increasing bank erosion, which introduces fine sediment into the water. Fine sediment, such as fine sand and silt, not only degrades water quality but also may fill the spaces between gravel particles or seal the bed with mud, damaging fish and aquatic in- sect habitat.10 Before the wolves arrived in the mid-1990s, willows and other streamside plants were nearly denuded by browsing elk. Since the arrival of the wolves, the elk population has dropped from almost 17,000 to approximately 4,600 in 2010.11,

Also, wolves were most successful in hunting elk along streams, where the elk had to negotiate the complex, changing topography. The elk responded by avoiding the dangerous stream environment. Over a four-year period, from 1998 to 2002, the number of willows eaten by elk declined greatly, and the riparian vegetation recovered. As it did so, the stream channel and banks also recovered and became more productive for fish and other animals.

In sum, although the reintroduction of wolves to Yellowstone is controversial, the wolves are a keystone species—a species that, even if not overly abundant, plays an important role in the ecological community, affecting the abundance of some species in the ecosystem indirect- ly. By hunting and killing elk and by scaring them away from the streams, wolves improve the stream banks, the water quality, and the broader ecologic community (in this case, the stream ecosystem). The result is a higher- quality stream environment.12 This takes us to the heart of a controversy over the reintroduction of wolves into Yellowstone National Park: improved riparian vegetation in the park but fewer elk to hunt outside the park. Some hunters are quite unhappy about this result.

Still, the debate about introduction of the wolf is complex. In Yellowstone, just over 90% of wolf prey is elk, and today there are far fewer bison and deer than there were before the wolf introduction. Land-use issues associ- ated with grazing for cattle and sheep are more difficult to assess. How we choose to manage wolf populations will reflect both science and values.10, 12

Wetlands

The famous cradle of civilization, the land between the Tigris and Euphrates rivers, is so called because the waters from these rivers and the wetlands they formed made possible one of the earliest sites of agriculture, and from this the beginnings of Western civilization. This well- watered land in the midst of a major desert was also one of the most biologically productive areas in the world, used by many species of wildlife, including millions of migra- tory birds. Ironically, the huge and famous wetlands be- tween these two rivers, land that today is within Iraq, have been greatly diminished by the very civilization that they helped create. “We can see from the satellite images that by 2000, all of the marshes were pretty much drained, except for 7 percent on the Iranian border,” said Dr. Curtis Rich- ardson, director of the Duke University Wetland Center.13

A number of events of the modern age led to the marsh’s destruction. Beginning in the 1960s, Turkey and Syria began to build dams upriver, in the Tigris and Euphrates, to provide irrigation and electricity. In 2009 there were 56 dams higher than 15 meters or with a reser- voir capacity larger than 3 million cubic meters!14

In the 1980s Saddam Hussein had dikes and levees built to divert water from the marshes so that oil fields under the marshes could be drilled. For at least 5,000 years, the Ma’adan people—the Marsh Arabs—lived in these marshes. But the Iran–Iraq War (1980–1988) killed many of them and also added to the destruction of the wetlands (Figure 10.8a and b).15

Today efforts are under way to restore the wetlands. According to the United Nations Environment Program, since the early 1970s the area of the wetlands has increased by 58%.15 But some scientists believe that there has been little improvement, and the question remains: Can ecosys- tems be restored once people have seriously changed them?

Prairie Restoration

Tallgrass prairie is also being restored. Prairies once occu- pied more land in the United States than any other kind of ecosystem. Today, only a few small remnants of prairie ex- ist. Prairie restoration is of two kinds. In a few places, one can still find original prairie that has never been plowed. Here, the soil structure is intact, and restoration is simpler. One of the best known of these areas is the Konza Prairie near Manhattan, Kansas. In other places, where the land has been plowed, restoration is more complicated. Never- theless, the restoration of prairies has gained considerable attention in recent decades, and restoration of prairie on previously plowed and farmed land is occurring in many midwestern states. The Allwine Prairie, within the city limits of Omaha, Nebraska, has been undergoing restora- tion from farm to prairie for many years. Prairie restora- tion has also been taking place near Chicago.

About 10% of North American original tallgrass prairie remains in scattered patches from Nebraska east to Illinois and from southern Canada south to Texas (in the Great Plains physiographic province of the United States). A peculiarity of prairie history is that although most prairie land was converted to agriculture, this was not done in cemeteries, or along roads and railroads; thus, long, narrow strips of unplowed native prairie remain on these rights-of-way. In Iowa, for example, prairie once covered more than 80% of the state—11 million hectares (28 million acres). More than 99.9% of the prairie land has been converted to other uses, primarily agriculture, but along roadsides there are 242,000 hectares (600,000 acres) of prairie—more than in all of Iowa’s county, state, and federal parks. These roadside and railway stretches of prairie provide some of the last habitats for native plants, and restoration of prairies elsewhere in Iowa is making use of these habitats as seed sources (Figure 10.9a).16

Studies suggest that the species diversity of tallgrass prairie has declined as a result of land-use changes that have led to the loss or fragmentation of habitat.16 For ex- ample, human-induced changes that nearly eliminated bison (another keystone species) from the prairie greatly changed the community structure and biodiversity of the ecosystem. Scientists evaluating the effects of grazing sug- gest that, managed properly, grazing by bison can restore or improve the biodiversity of tallgrass prairie16 (Figure 10.9b). The effect of grazing by cattle is not as clear. Range managers have for years maintained that cattle grazing is good for ecosystems, but such grazing must be carefully managed. Cattle are not bison. Bison tend to range over a wider area and in a different pattern. Cattle tend to stay longer in a particular area and establish grazing trails with denuded vegetation. However, both cattle and bison, if too many of them are left too long in too small an area, will cause extensive damage to grasses.

Fire is another important factor in tallgrass prairies. Spring fires enhance the growth of the dominant tall grasses that bison prefer. Tallgrass prairie is a mixture of taller grasses, which prefer warm, dry environments, and other grasses, forbs, and woody plants, which prefer cool- er, wetter conditions. The tall grasses often dominate and, if not controlled by fire and grazing, form a thick cover (canopy) that makes it more difficult for shorter plants to survive. Grazing opens the canopy and allows more light to reach closer to the ground and support more species. This increases biodiversity. Long ago, fires set by light- ning and/or people helped keep the bison’s grazing lands from turning into forests. Today, ecological restoration has attempted to use controlled burns to remove exotic species and woody growth (trees). However, fire alone is not sufficient in managing or restoring prairie ecosystem biodiversity. Moderate grazing is the hypothetical solu- tion. Grazing of bison on degraded grassland will have negative impacts, but moderate grazing by bison or cattle on “healthy prairies” may work.

One of the newest threats to tallgrass prairie ecosys- tems is atmospheric nitrogen from automobile emissions. Nitrogen helps some species, but too much of it causes problems for tallgrass prairie ecosystems, whose diver- sity and productivity are significantly influenced by the availability of nitrogen. Fire and millions of grazing bison regulated nitrogen availability during prehistoric and pre- automobile times.

Another example of restoration is found in A Closer Look 10.1; in this case ecologists managed species to save the island fox.

10.4 Applying Ecological Knowledge to Restore Heavily Damaged Lands and Ecosystems

An example of how ecological succession can aid in the restoration (termed reclamation for land degraded by mining) of heavily damaged lands is the ongoing effort to undo mining damage in Great Britain, where some mines have been used since medieval times and approximately 55,000 hectares (136,000 acres) have been damaged. Res- toration of coal-mined areas, especially from strip mining, is an important need in the United States as well. The U.S. Surface Mining Law—the Abandoned Mine Land Rec- lamation Program—provides for the restoration of lands mined and abandoned or left inadequately restored before August 3, 1977. More than $3.5 billion has been spent through this law on restoration of coal mining land.17

Restoration of lands that are abandoned coal mines is now accomplished through a coal production tax, levied on operators of mine at $0.12/ton of underground mined coal and $0.135/ton of surface mined coal. By 2011, more than $7.2 billion had been spent from these funds to reclaim more than 295,000 acres.18 According to the U.S. Office of Surface Mining Reclamation and Enforcement, “Environ- mental problems associated with abandoned mine lands include surface and ground water pollution, entrances to open mines, water-filled pits, unreclaimed or inadequately reclaimed refuse piles and mine sites (including some with dangerous high walls), sediment-clogged streams, damage from landslides, and fumes and surface instability resulting from mine fires and burning coal refuse. Environmental restoration activities under the abandoned mine reclama- tion program correct or mitigate these problems.18

The success of coal mining restoration remains con- troversial. On one side are reports such as that from the Clean Air Task Force, which states that “hundreds of thousands of acres of surface mines have not been re- claimed, and reclamation of steep terrain, such as found in Appalachia, is difficult.19 Finally, despite reclamation efforts, an ecosystem may be destroyed and replaced by a totally different habitat.”

On the other side, associations of coal mining corpo- rations claim restoration has been done successfully. An example of a successfully restored surface mine is shown in Figure 10.12.21

Recently, programs have been initiated to remove tox- ic pollutants from the mines and mine tailings, to restore these damaged lands to useful biological production, and to reclaim the attractiveness of the landscape.22

One area damaged by a long history of mining lies within the British Peak District National Park, where lead has been mined since the Middle Ages and waste tailings are as much as 5 m (16.4 ft) deep. The first attempts to re- store this area used a modern agricultural approach: heavy application of fertilizers and planting of fast-growing agri- cultural grasses to revegetate the site rapidly. These grasses quickly green on the good soil of a level farm field, and it was hoped that, with fertilizer, they would do the same in this situation. But after a short period of growth, the grasses died. The soil, leached of its nutrients and lacking organic matter, continued to erode, and the fertilizers that had been added were soon leached away by water runoff. As a result, the areas were shortly barren again.

When the agricultural approach failed, an ecologi- cal approach was tried, using knowledge about ecological succession. Instead of planting fast-growing but vulner- able agricultural grasses, ecologists planted slow-growing native grasses, known to be adapted to mineral-deficient soils and the harsh conditions that exist in cleared areas. In choosing these plants, the ecologists relied on their observations of what vegetation first appeared in areas of Great Britain that had undergone succession naturally.22 The result of the ecological approach has been the success- ful restoration of damaged lands (Figure 10.13).