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Science and Strategies for Restoring the Earth
By John J. Berger
ISLAND PRESSCopyright © 1990 Restoring the Earth
All rights reserved.
AGRICULTURAL LANDS BARRENS, COASTAL ECOSYSTEMS, PRAIRIES, AND RANGELANDS
THE RESTORATION OF AGRICULTURAL LANDS AND DRYLANDS
DAVID A. BAINBRIDGE
ABSTRACT: Throughout the world, drylands used for agriculture and grazing are deteriorating. In the United States, drylands are also experiencing moderate-to- severe desertification and declining productivity. Lands once productive and profitably are being abandoned as a result of declining fertility, increased sensitivity to drought, high water tables, salinization, and groundwater overdrafts. Farmland productivity in humid and subhumid areas of the world is also declining as a result of unsustainable management practices. These lands can be restored by reversing the social and ecological factors that led to their deterioration and by establishing new incentives for restoration.
KEY WORDS: drylands, farmland, rangeland, restoration, reforestation, revegetation.
THE WORLD'S AGRICULTURAL lands and drylands are deteriorating as a result of mismanagement. Fertility of agricultural lands is declining, erosion is widespread, and production increases are not matching population gains in many areas.
The drylands are in the worst condition, as a result of inappropriate agricultural practices, overgrazing, and tree cutting for fuel. Recent estimates place the worldwide area of land affected by moderate-to-severe desertification at 22.5 million km2 (Dregne 1986), an area two and one half times the size of the United States. More than a fourth of the drylands of the United States are more than moderately desertified.
The deterioration of these lands can be measured by the reduced productivity of desirable plants, alterations in biomass and diversity of the micro-and macrofauna, accelerated soil erosion, and increased risk for human occupants. The causes for this decline in drylands productivity include overgrazing, inappropriate dryland cultivation, overpumping of groundwater, deforestation, and poor drainage of irrigated lands (Sheridan 1986).
The problems of farmland deterioration in the United States first received national attention during the Dust Bowl years of the 1930s. After the Second World War new forces emerged that encouraged further land degradation. Foremost among these were the massive irrigation schemes of the West; the development of farm chemicals which offered the illusion of fertility maintenance; and the short-term control of pests and diseases needed to grow extensive monocultures of the same crop year after year. These problems were compounded by government research and regulatory programs which subsidized chemicals, energy, water, and commodities without concern for environmental or social impact.
The area of agricultural land that has been abandoned in the United States is not known, but Pimentel et al. (1976) suggested that an estimated 80 million ha have been either totally ruined for crop production or so heavily damaged as to be only marginally productive.
Range deterioration in the United States was most catastrophic in the late 1800s as a result of serious overstocking. Within this period the carrying capacity of the California range was reduced by half (Burcham 1957).
Land deterioration results from complex interactions of cultural and ecological factors. Finding solutions that will both prevent further decline and restore degraded lands will require an approach that combines ecological, technical, and cultural understanding of these problems. Developing restoration programs that work in the United States will provide a sound base for addressing similar problems elsewhere in the world.
RESTORING AGRICULTURAL LANDS
Most of the land suited for continued agricultural production is already in production but much is in very poor condition. The elements of a restoration program for farmland will depend on the soil, climate, cropping system, market, and the farmer's experience and skill. In general, a restoration program will include a decreased emphasis on chemical inputs, an increased diversity of crops, and an attempt to mimic the structure and function of natural ecosystems. In many cases, trees and animals are included in the farm system to provide better utilization of the farm resources.
A restoration program will often include: subsoiling or deep chiseling to break up compacted soil and facilitate root growth (Sykes 1946); use of manure, mulch, compost, or green manures to restore soil organic matter and biological activity, and improve soil structure and tilth (Pieters 1927; Turner 1951); primary reliance on biological nitrogen fixation rather than commercial fertilizers (Subba Rao 1982); conversion from moldboard plowing to conservation tillage (Sprague and Triplett 1986); establishment of a rotation program; intercropping and/or multiple cropping (Francis 1986); development of integrated pest management programs that maximize use of biological controls and minimize use of chemical controls (Huffaker and Messenger 1976); and establishment of windbreaks, hedgerows, and drain channel vegetation to control erosion (Bennett 1939). In addition the farm program should include a monitoring program to track conditions in each field and to ensure that both macro- and micronutrients removed in harvested crops are replaced.
Many excellent farm restorations have been achieved by improved management (Howard 1943; Berry 1981). Agricultural land restoration will be aided by the development of perennial grains and tree crops which can be grown with limited inputs and beneficial environmental impacts in areas where production of conventional annual crops can be very destructive (Jackson 1980; Bainbridge 1986; Wagoner 1986).
Restoring abandoned agricultural land can be relatively easy and economical because conventional farm equipment can be used for cultivation and seeding. Thousands of hectares of abandoned agricultural land have been restored to productive use as rangeland in the western United States. In southeastern Oregon, for example, range managers estimate that the livestock carrying capacity was doubled by restoration efforts (Heady and Bartolome 1976).
The low value and limited economic potential of much of this abandoned land makes low-cost restoration essential. Although long-term fallow periods will lead to revegetation in some cases, the native seed stock is commonly exhausted, and the soil structure and fertility have deteriorated sufficiently to limit or prevent revegetation. Where funding is limited, treatment may have to be limited to pitting or imprinting to increase surface roughness and infiltration. If more money is available, direct seeding with mixes of forbs, grasses, shrubs, and trees can be added.
Restoration of agricultural land in subhumid and humid areas is much easier than in arid areas; extensive areas of the United States that were in poor condition have been reforested by natural processes. In New England, for example, where the boom years for farming in the mid1800s led to extensive conversion of forest to agricultural use, most of the marginal land has now reverted to forest. In the southeastern United States, direct seeding of oaks has proved effective for reforesting abandoned farmland (Krinard and Francis 1983), and trees should be an integral element in most restoration schemes (Smith 1988).
Every year more than a million hectares of agricultural land is developed for housing, highways, and other uses. Much of this land could be kept in production if development were more wisely managed. Village Homes, a 200-unit residential development in Davis, California, kept more than 17% of the land area in agricultural use (Bainbridge et al. 1978).
Some of the little known yet important factors that are involved in restoration of drylands are the living soil crust, soil structure, chemistry, microbiology, microsite differences, and fire.
Soil crusts include lichens, ferns, algae, and other cryptogams. Cryptogamic crusts have been ignored by range managers until recently, despite early suggestions that they might be important for plant establishment (Booth 1941). More recent studies have shown that grazing can degrade the cryptogamic crust (Anderson et al. 1982) and reduce infiltration (Loope and Gifford 1972).
Other recent work on the effects of grazing on soil properties and plant succession has demonstrated the importance of microsite changes and the role these play in determining which species increase and which decrease (Eckert et al. 1987). They found that moderate trampling encouraged the establishment of desirable plants on range in excellent condition, but led to further deterioration of land in poor condition.
Fire was used extensively by indigenous people to manage vegetation. Fires of natural origin also strongly influence the course of plant succession. Fire suppression may have many unintended and unwanted effects and should be more carefully considered in land management (Minnich 1987). Fire is an important tool for grassland management and restoration (Berger 1985).
Dryland restoration is made difficult by the limited potential for immediate return on investment. Sheridan (1986) estimated that the cost of dryland restoration ranges from $60-3,000/ha. Presentations at the Second Native Plant Revegetation Conference held in San Diego (Rieger and Steele 1987) made it clear that even larger expenditures can lead to poor results if ecological and soil factors are not considered. Attempts to reestablish native vegetation without restoring native soil conditions failed completely in many cases. Yet plant establishment and restoration have been successful when ecological considerations are properly addressed (Virginia and Bainbridge 1987; Khoshoo 1987).
PRINCIPLES OF SUCCESSFUL RESTORATION
The foundation of an economical and successful restoration program is a clear understanding of the environment and the plants, animals, and people involved. A restoration program should begin with a study of the history of the land, its native vegetation (and human influences), the soil characteristics of comparable undisturbed native soils, and as much information as possible on the interactions between plants, animals, and humans. When this information is available, a draft plan for restoration can be developed.
The second step should be a series of test plots to evaluate the strategies for restoration that appear promising. This is particularly important in areas where little information is available. While the test plots are underway, a seed-collection program should be initiated, and seed nurseries should be established if needed to increase seed stocks.
The essential elements of a minimum-cost restoration effort are the introduction of appropriate seeds and related symbionts to microsites that provide suitable soil and moisture conditions for rapid root growth and plant establishment. This may include preparation of the soil by deep ripping, chiseling, and/or discing; application of soil crust inoculum (St. Claire et al. 1986); seeding with a complex mix of species inoculated with appropriate symbionts (St. John 1985; Virginia and Bainbridge 1986); and imprinting (Dixon 1982). Weed control can help slow-growing native plants to compete. Controlled burning at the time weed species are most vulnerable (Haverkamp et al. 1987) or soil solarization (Horowitz et al. 1983) can provide weed control without chemicals. Solarization involves moistening the soil and covering it with transparent plastic, letting the sun heat the soil, thereby killing weed seeds and many pathogens.
Other low-cost techniques that have been successful include the use of discs that have been modified to create pits which provide a variety of microsites and collect water. Large pits were found to be generally more effective than small pits in arid areas (Medina and Garza 1987). Pits are most effective on slopes of less than 8% where natural infiltration is limited (Vallentine 1980).
When very little money is available, the best option is simply to roughen up the soil surface. A rough surface increases infiltration and traps blowing soil and seeds. On some soils an imprinter would be most appropriate for roughening; others would benefit from use of a plow or disc pitter. This can often be done for less than $50/ha.
More expensive treatments will provide more rapid revegetation. These treatments might include ridging, catchment basins, mulch, and pest control. Ridging provides many benefits, including water collection and development of a microsite gradient that should provide favorable conditions for seeds over a wide range of precipitation (Medina and Garza 1987). Ridging is also very effective in areas that may experience waterlogging or standing water (Bainbridge 1987). Micro- and macrocatchment basins may also be used to aid in establishing vegetation (Shanan et al 1970).
Mulching and composting can also provide many benefits. Native grasses with seed are excellent for mulching if they are available (Wenger 1941; Schiechtl 1980), but straw is also of value. High application rates, from 5-10 tons/ha, with crimping to retain the straw, are desirable, particularly on erosive slopes (Schiechtl 1980; Kay 1987). Compost is also of value.
Other restoration program elements that may be of value include pest control (cages or fencing to protect plants), rodent control, limited irrigation, and fertilizer. Fertilizer should be used with care because it may increase shoot rather than root growth, increase weed competition, depress microsymbiont development, and make plants more palatable for pests. Adams et al. (1987) found that even a slow release fertilizer decreased transplant survival in all cases and by as much as 90% in the worst case. Similar problems might be expected with direct seeding, and few experienced revegetation groups in the California deserts used fertilizer of any kind except on cut slopes and exposed subsoil (Virginia and Bainbridge 1986).
Transplants are expensive but make it possible to establish plants that are not easily started from seed in the field. Containers and nursery management should enable plants to develop a root system (with symbionts) suited for survival in a difficult environment. Deep containers may provide substantial benefits in this regard (Virginia and Bainbridge 1986). Transplants will usually require cages or screens to reduce grazing pressure from insects, rodents, livestock, and deer.
Timing of transplanting can be critical for establishment. Transplanting in the desert may be feasible only after a flood event. Lovenstein (1988) has achieved 95% establishment in the Negev Desert at such times. Even transplants that die may provide some cover and increase establishment of seedlings.
It may be desirable to combine expensive treatments, i.e., transplants, on a very limited area (1-2%), with contour strip treatments, i.e., pitting and direct seeding, on a larger area (perhaps 10—20%). This approach can establish seed sources for subsequent natural revegetation of the remaining land. Heady and Bartolome (1976) found that revegetating 10% of the land in their study area had a very positive effect on the remaining 90% by reducing grazing pressure.
SUPPORTING RESTORATION EFFORTS
The key to developing a large-scale restoration movement is improving the understanding of ecological principles and land management in the general population (Bainbridge 1985). This can be done by developing appropriate curricula for colleges and schools. The reestablishment of a Civilian Conservation and Restoration Corps could also be included to provide training in the methods of restoration and field research.
One of the most important and currently neglected areas is the development of an accurate understanding of the condition and trends in land use and condition. The establishment of a U.S. Ecological Survey (U.S.E.S.) with status and funding comparable to the U.S. Geological Survey would be appropriate to undertake baseline monitoring and restoration studies. The general outlines for a national biological survey have been developed (Kim and Knutson 1986) and would provide a good starting point for the U.S.E.S., although it should have a strong restoration research and demonstration program. Much of the work could be done under long-term, ten-year cycle, competitive grants.
Excerpted from Environmental Restoration by John J. Berger. Copyright © 1990 Restoring the Earth. Excerpted by permission of ISLAND PRESS.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of Contents
ContentsABOUT ISLAND PRESS,
PART I - RESTORATION OF LAND,
AGRICULTURAL LANDS BARRENS, COASTAL ECOSYSTEMS, PRAIRIES, AND RANGELANDS,
TEMPERATE FORESTS AND WATERSHEDS,
SOIL BIOENGINEERING AND REVEGETATION,
URBAN ISSUES, PARKS, AND WASTE TREATMENT,
SOLID, TOXIC, AND RADIOACTIVE WASTE MANAGEMENT,
PART II - RESTORATION OF AQUATIC SYSTEMS,
ESTUARIES, RIVERS, AND LAKES,
FISHERIES AND STREAMS,
FRESH- AND SALTWATER WETLANDS, SEAGRASS BEDS, AND VERNAL POOLS,
PART III - STRATEGIC PLANNING AND LAND ACQUISITION FOR RESTORATION,
RESTORING THE EARTH: THE ORGANIZATION,
CONFERENCE PAPERS AND TAPES,
ABOUT THE EDITOR,
ALSO AVAILABLE FROM ISLAND PRESS,
ISLAND PRESS BOARD OF DIRECTORS,