Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 353
BioDiversity PART 9 ALTERNATIVES TO DESTRUCTION
OCR for page 354
BioDiversity Traditional Indonesian rice paddies, which contain numerous indigenous varieties of rice. Photo courtesy of Miguel A.Altieri.
OCR for page 355
BioDiversity CHAPTER 40 ARE THERE ALTERNATIVES TO DESTRUCTION? MICHAEL H.ROBINSON Director, National Zoological Park, Washington, D.C. Any consideration of the forces tending to produce drastic reductions in biodiversity must concentrate on habitat destruction. To slow down, ameliorate, or prevent habitat destruction we need to understand the forces that cause it. There is a widespread assumption that habitat destruction, particularly in the Third World, is caused by ignorance or stupidity or both. This assumption is reflected in the philanthropic funding of environmental education programs and in attempts to seed environmental defense organizations in Africa, Latin America, and Asia. It is often assumed that these efforts are constructive. The contrary viewpoint is that environmental destruction results from economic pressures that have nothing to do with stupidity or ignorance. It is certainly arguable that given the present international distribution of wealth, the mainly tropical less-developed countries will be forced to exploit their natural resources on a massive scale in order to try to raise living standards quickly. A discussion of whether they can do this is beyond the scope of this chapter and beyond my competence; the majority of the countries involved are certainly trying. In this volume are a number of analyses of the causes of habitat destruction and the economic realities facing the Third World. Most tropical deforestation, and with it the major threat to biological diversity, comes from efforts to increase the level of subsistence and to generate foreign exchange for the purchase of goods manufactured in the developed world. To halt destruction we must find alternative means of providing subsistence goods (food, fuel, and construction materials) and alternative commodities to replace those resulting from environmental rape. There is a third logical possibility that is almost certainly not a real one. That is for the entire world to adopt voluntary restraints on resource exploitation and living standards. This is the pathway of so-called green politics and the small-is-beautiful
OCR for page 356
BioDiversity concept. On this there seems to be unanimity of opposition from all conventional political movements from the capitalist right to the Marxist left. I would contend that the discovery of alternatives to destruction can come from the results of purely basic (i.e., nonapplied) studies. I have developed this theme in detail elsewhere (Robinson, 1985, 1986). In Chapter 42 of this volume, Rubinoff deals in detail with the scheme that we developed in Panama—a scheme based on the principle that native species of plants and animals should be considered for domestication and cultivation, as opposed to the use of exotics introduced at the behest of the developed world. In Panama, the animal studies include the green iguana (Iguana iguana), a large folivorous lizard, and the paca (Cuniculus paca), a caviomorph rodent widely esteemed for its succulence. Both these animals had been the subject of numerous academic studies before being considered as potential alternatives to destruction. The National Research Council’s Board on Science and Technology for International Development, on the other hand, has deliberately set out to search for animals that have a high potential for domestication or husbandry (NRC, 1983). This approach was thus project-oriented from the start. Both approaches are valid and potentially productive. The purist approach has some exciting implications. Tropical regions are often the scene of highly coadapted/coevolved communities of plants and animals. It would seem that these communities should, a priori, be the place to search for exploitable bioresources that can be used by humans. They can be regarded as having a high potential for containing species that are preadapted for human use. As an example of this we can briefly consider the paca. This rodent lives on the floor of rain forests in Central and South America. Its activity is nocturnal. These facts set the scene for its potential utility. Because it lives on the forest floor, does not climb trees, and is a rodent, it has a proscribed food source. It feeds on fruits that fall to the ground from the trees and to a much lesser extent on roots and seedlings. It utilizes the secondary products of the forest that are unavailable to humans and most grazing animals (exotic or indigenous). Fruitfall in the humid tropics is sporadic, but the paca subsists on an intermittent food supply by scatter hoarding during times of plenty (intermittent fruitfall may be an interspecific adaptation to ensure dispersal; Smythe, 1970). Thus pacas can prosper without destroying forest. They are almost tailor-made for domestication. Being nocturnal they do not need the capacity to run long distances to escape predators. They can be fat, unlike their diurnal complementary species the agouti (Dasyprocta spp.). Their disadvantages are a low reproductive rate, small families, and solitary social life. In other parts of the world, there have been similar adaptations in response to similar environmental and biological pressures. The bearded pig (Sus barbatus), found in Borneo, Java, and the Philippines, is a forest floor fruit eater, grows to a substantial size, and copes with intermittent or seasonal fruit supplies by migration from area to area. It is clearly a candidate for exploitation within the forest (NRC, 1983; Robinson, 1986). There are similar adapted animals in Australasia, despite the absence of large placental animals there. The tree kangaroo (Dendrolagus spp.) is a leaf-eating arboreal animal that might prove to be as suitable for domestication as the iguana. In Malaysia and throughout the Indian subcontinent and Southeast
OCR for page 357
BioDiversity Asia there are giant squirrels, and so on. As we contemplate the mass extinction of tropical animals, we can speculate that if it were not for a dramatic historical extinction we might be considering the dodo (Raphus cuculatus) as a candidate for domestication and transtropical exploitation. This giant (25-kilogram) pigeon was flightless and probably subsisted on fruits, just like the paca! Just as the dispersal strategies of some Neotropical trees seem to have coevolved with the pacas, so, it seems, have some of the Mauritian fruits coevolved with the dodo. Temple (1977) suggested that the hard, nutlike seed of Calvaria major depended for its germination on its abrasion in the gizzard of the dodos. Janzen and Martin (1982) suggested that at least 30 species of trees in Costa Rica depended for their dispersal on the digestive processes of some now extinct, large (sometimes giant), herbivores of the Neotropics. These, like the dodo, were probably eminently edible. Similarly, the giant ground sloths of South America and the giant birds of New Zealand, known from historic times, could have been candidates for domestication. This is not fruitless speculation but a notice that our regrets about these extinctions are certainly likely to be matched soon by more massive regrets about the ongoing and imminent extinctions. Our knowledge of plants with a high potential for future exploitation is very sketchy indeed. The Board on Science and Technology for International Development within the National Research Council has highlighted some examples (NRC, 1975, 1979, 1981, 1984, 1985). In Chapter 10 of this volume, Iltis has drawn attention to some other dramatic examples. Again on a priori grounds we can predict that there must be many plants that have or are in themselves valuable, undiscovered products. The tropical forests of the world are the most intense battlegrounds for species competition on the face of the Earth. This intensity is a direct result of extraordinary biodiversity and the continuingly ferocious evolutionary arms race. Huge assemblages of animal species eat leaves, and it is no exaggeration to say that tropical plants must have evolved a formidable array of insecticidal compounds and insect deterrents. We already use some of these. The picture is similar in the case of fungicides. The moist tropical forest is a superb environment for fungi of all kinds. Fungi relish warmth, wetness, and an abundance of organic substrates. The leaves of tropical trees are not only assaulted by insects and other animals but also by fungi and epiphyllic plants. What a place to look for fungicides and herbicides! An illustration of how fundamental studies lead to discoveries in this field comes from a report of the food preferences of leaf-cutter ants by Hubbell et al. (1983). They found that leaf-cutter ants (Atta sp.) rejected the leaves of the leguminous tree Hymenaea courbaril. Such leaves kill the fungus that the ants grow in their nests as a food resource. It is entirely improbable that the tree evolved the fungicide to deter leaf-cutter ants. Rather, it probably had to cope with a broad spectrum of epiphyllic fungi and evolved a broad-spectrum fungicide to (literally) keep its leaves clean. Laboratory tests on the fungicide, a terpene-caryophyllene epoxide, show antifungal activity against a wide range of pathogenic fungi. This precisely illustrates the points I make above. It surely means that we can confidently predict, because of the nature of tropical forest ecology, that its plants should be a source of a wide range of useful products. These await discovery. There is little doubt that
OCR for page 358
BioDiversity among them are further alternatives to destruction. In terms of food sources we already exploit tropical plants as sources of oils, fats, carbohydrates (sugars as well as starches), and proteins, but the current number of species that we use for food is very small. Discovering potential forest crops is going to require a massive research effort, but we can expect some shortcuts. These are outlined below. First, we have a great potential source of insights in ethnobotany and ethno-zoology. Populations of humans throughout the world have existed in essentially harmonious relationships with tropical rain forests for centuries. Many of these relationships involved sustained yield subsistence use of the forests, and the Mayans produced a surplus of foodstuffs without destroying vast areas of forest. There are thus a wide range of peoples with invaluable knowledge about plants and animals. This knowledge may not be expressed in the terminology of modern science; it may be interlaced with magic, myth, and superstition, but it is certainly extractable. Just as certainly, its extraction is a matter of extreme urgency, since the folkways of forest peoples are disappearing more rapidly than the plants and animals that they have learned to exploit. In Part 2 of this volume, Nations, Farnsworth, Iltis, and Plotkin address various aspects of our need to utilize traditional knowledge—knowledge that is threatened and fragile. It is not merely knowledge of species but also knowledge of practices of husbandry, gardening, and agriculture. In Chapter 41, Altieri argues persuasively for the modern applications of ancient systems of mixed cropping as means of ex situ preservation of diversity. In addition to traditional knowledge, there is another shortcut to research into alternatives. This second method is implied in much of what I have already argued above. We have, in my opinion, a virtually untapped resource in the insights of tropical biologists. Experienced tropical biologists are potentially a source of major advances; they should be able to identify systems that are sources of evolutionary strategies that are preadapted to nondestructive parasitization by humans. To apply such intuitions is going to require a change of attitude on the part of many academic biologists. They will have to recognize that elegant theoretical generalizations, intellectually exciting and satisfying as they may be, are not their only responsibility to science and society. We must become concerned about the future of tropical mankind, even if only because this is the only way we can preserve tropical nature. Janzen’s application of his extensive theoretical insights to the practical problems involved in regrowing tropical forests is a shining example to us all (see Chapter 14). The involvement of several Smithsonian biologists in research on alternatives to destruction is another excellent sign. We should also realize that sciences other than biology may be able to make substantial contributions to halting environmental destruction. An incalculable pressure is exerted on forests worldwide by fuelwood gathering. Eckholm (1975) has estimated that 1.5 billion people derive more than 90% of their fuel needs from wood, while another billion derive at least 50% from wood. Most of these people use extremely inefficient stoves, many with efficiencies less than 10%. The invention of an efficient and inexpensive wood-burning stove could greatly reduce the subsistence pressures on tropical forests. While all the initiatives and possibilities mentioned above give cause for hope, although certainly not cause for optimism, there is still another area from which
OCR for page 359
BioDiversity alternatives to destruction might be derived. This is the area of radical innovation. Instead of trying to solve problems by applying existing techniques or improving them, it is possible that we can discover new approaches that are so disjoined from present approaches that they qualify as breakthroughs or new scientific revolutions. The woodgrass system proposed by Shen in Chapter 43 has all the earmarks of a revolutionary approach. It is very simple in concept: in trees, there is a comparatively large increase of biomass in the first years of growth. The growth curve is most efficiently cropped at its maximum angle. At this stage, trees are thin and useless as sources of board timber. But they can be harvested by techniques more appropriate to hay production and the product then subjected to treatment as cattle fodder, composition boards and beams, fuelwood, and so on. The agricultural management of trees as if they were essentially grasses is surely revolutionary. This kind of approach needs to be applied to our whole approach to tropical problems. Finally, there must be a realization that present levels of research into all the matters relating to tropical ecosystems, natural and man-made, terrestrial and marine, is totally and fundamentally inadequate. It is scientifically invidious to compare research expenditures on astronomy and tropical biology, but this does serve to point to the neglect of studies of life on Earth. Astronomical studies are important; they are contributing fundamentally to knowledge, but the stars are not about to disappear. A world expenditure on fundamental studies of tropical biology that is less than half the cost of a Boeing 747 airliner is a sad reflection on both our priorities and our values. REFERENCES Eckholm, E. 1975. The Other Energy Crisis: Firewood. Worldwatch Paper 1. Worldwatch Institute, Washington, D.C. 20 pp. Hubbell, S.P., D.F.Wiemer, and A.Adejare. 1983. An antifungal terpenoid defends a neotropical tree (Hymenaea) against attack by fungus-growing ants (Atta). Oecologia 60:321–327. Janzen, D.H., and P.S.Martin. 1982. Neotropical anachronisms: The fruits the gomphotheres ate. Science 215:19–27. NRC (National Research Council). 1975. Underexploited Tropical Plants with Promising Economic Value. Board on Science and Technology for International Development Report 16. National Academy Press, Washington, D.C. 187 pp. NRC (National Research Council). 1979. Tropical Legumes: Resources for the Future. Board on Science and Technology for International Development Report 25. National Academy Press, Washington, D.C. 331 pp. NRC (National Research Council). 1981. The Winged Bean: A High Protein Crop for the Tropics. Board on Science and Technology for International Development Report 37. National Academy Press, Washington, D.C. 49 pp. NRC (National Research Council). 1983. Little-Known Asian Animals with a Promising Economic Future. Board on Science and Technology for International Development Report 46. National Academy Press, Washington, D.C. 133 pp. NRC (National Research Council). 1984. Amaranth: Modern Prospects for an Ancient Crop. Board on Science and Technology for International Development Report 47. National Academy Press, Washington, D.C. 76 pp. NRC (National Research Council). 1985. Jojoba: New Crop for Arid Lands. Board on Science and Technology for International Development Report 53. National Academy Press, Washington, D.C. 102 pp. Robinson, M.H. 1985. Alternatives to destruction: Investigations into the use of tropical forest resources with comments on repairing the effects of destruction. Environ. Prof. 7:232–239.
OCR for page 360
BioDiversity Robinson, M.H. 1986. The Biological Resources of Southeast Asia and Future Development. Paper presented at ASEAN Science and Technology Conference, Kuala Lumpur, Malaysia, 29 April 1986. Smythe, N. 1970. Relationships between fruiting seasons and seed dispersal methods in a neotropical forest. Am. Nat. 104(935):25–35. Temple, S.A. 1977. Plant-animal mutualism: Coevolution with Dodo leads to near extinction of plant. Science 197:885–886.
OCR for page 361
BioDiversity CHAPTER 41 AGROECOLOGY AND IN SITU CONSERVATION OF NATIVE CROP DIVERSITY IN THE THIRD WORLD MIGUEL A.ALTIERI Associate Professor, Division of Biological Control, University of California, Berkeley LAURA C.MERRICK Graduate Research Assistant, Department of Vegetable Crops, University of California, Davis, and L.H.Bailey Hortorium, Cornell University, Ithaca, N.Y. Today, the foundation and health of agriculture in industrial countries largely depend on their access to the rich crop genetic diversity found in Third-World countries. Yet the very same germplasm resources most sought after for their potential applications in biotechnology are constantly threatened by the spread of modern agriculture. On the one hand, the adoption of high-yielding, uniform cultivars over broad areas has resulted in the abandonment of genetically variable, indigenous varieties by subsistence farmers (Frankel and Hawkes, 1975; Harlan, 1975). The new varieties are often less dependable than the varieties they have replaced when grown under traditional agricultural management (Barlett, 1980). On the other hand, the planting of vast areas with monocultures of genetically uniform cultivars makes agricultural productivity extremely vulnerable to yield-limiting factors, as illustrated by the southern corn leaf blight epidemic in the United States in 1969–1970 (Adams et al., 1971). Agroecosystems established far from centers of origin tend to have simpler genetic defenses against pathogens and insect pests, rendering crops more vulnerable to epidemic attack—a situation that rarely occurs in an unmodified traditional agroecosystem (Segal et al., 1980). Concern for this rapid loss of genetic resources and crop vulnerability consolidated at the international level about 13 years ago with the establishment of the International Board for Plant Genetic Resources (IBPGR), which coordinates a global network of gene banks to provide plant breeders with the genetic resources
OCR for page 362
BioDiversity necessary to develop better crops. International efforts have so far placed more emphasis on increasing yield than on maintaining stable harvests (Plucknett et al., 1983)—an emphasis that has provided the justification for technological innovation and transfer in a manner not reflecting indigenous social, ecological, and ethnobotanical considerations. Landraces1 and wild relatives of major crops are collected from their native habitats, and the seed or vegetative material is placed in gene banks for storage or breeding collections for evaluation and potential use (Frankel and Bennett, 1970). Although ex situ conservation methods have contributed to the improvement of certain crops and the storage of the germplasm of a variety of major crops (Frankel and Bennett, 1970), they do not provide a panacea for conserving natural sources of crop genetic resources (Oldfield, 1984). A major problem is that seed storage freezes the evolutionary processes by preventing new types or levels of adaptations or resistance to evolve, because plants are not allowed to respond to the selective pressures of the environment (Simmonds, 1962). In addition, ex situ methods remove crops from their original cultural-ecological context (Nabhan, 1985)—the human-modified systems in which they evolved. As Wilkes (1983, p. 136) stated, “The centers of genetic variability are moving from natural systems and primitive agriculture to gene banks and breeders’ working collections with the liabilities that a concentration of resource (power) implies.” Controversy has already erupted around the control of gene banks, since countries such as Colombia, Cuba, Libya, and Mexico question the free access to genetic resources by industrial countries. In the industrial countries, breeders develop new commercial varieties, often using valuable genes derived from landraces or wild species originally collected in the Third World. Then, the new commercial varieties are sold back to the Third World at considerable profit (Wolf, 1985). A number of scientists have emphasized the need for in situ conservation of crop genetic resources and the environments in which they occur, since in situ conservation allows for continued, dynamic adaptation of plants to the environment (Nabhan, 1985; Prescott-Allen and Prescott-Allen, 1982; Wilkes, 1983). For agriculture, this phenomenon is particularly important in areas under traditional farming, where crops are often enriched by gene exchange with wild or weedy relatives (Harlan, 1965). However, most researchers consider that in situ preservation of landraces would require a return to or the preservation of microcosms of primitive agricultural systems—to many, an unacceptable and impracticable proposition (Ingram and Williams, 1984). Nevertheless, we contend that maintenance of traditional agroecosystems is the only sensible strategy to preserve in situ repositories of crop germplasm. Although most traditional agroecosystems are undergoing some process of modernization or drastic modification, conservation of crop genetic resources can still be integrated with agricultural development, especially in regions where rural development projects preserve the vegetational diversity of traditional agroecosystems and depend upon the peasants’ rationale to utilize local resources and their intimate knowledge of the environment (Alcorn, 1984; Nabhan, 1985; Sarukhan, 1985). 1 Landrace populations consist of mixtures of genetic lines, all of which are reasonably adapted to the region in which they evolved but which differ in reaction to diseases and insect pests.
OCR for page 363
BioDiversity In alternative strategies, the conservation of plant genetic resources and agricultural development by peasants can be considered simultaneously. In a recent article (Altieri and Merrick, 1987), we suggested the best ways in which traditional varieties, agroecological patterns, and management systems can be integrated into rural development programs to salvage crop genetic resources. These are reviewed below. PEASANT AGRICULTURE AND CROP GERMPLASM RESOURCES The stability and sustainability of traditional agriculture are based on crop diversity (Altieri and Merrick, 1987; Chang, 1977; Clawson, 1985; Egger, 1981; Harwood, 1979). The peasant’s strategy of hedging against risk by planting several species and varieties of crops in different spatial and temporal cropping systems designs is the most effective long-lasting means of stabilizing yields. Although improved varieties are distributed throughout Third-World countries, they have made serious inroads in areas strongly linked to commercial agriculture and the national market, where they have hastened the disappearance of wild relatives and traditional varieties of crops (Brush, 1980). Thus today, the rural landscapes consist of mosaics of modern and traditional varieties and technologies (Figure 41–1). As areas become more marginal in natural resources and in infrastructural support, however, the use of improved varieties declines; farmers abandon them because of FIGURE 41–1 A traditional small farm system in Tlaxcala, Mexico, exhibiting a corn-alfalfa strip-cropping pattern, borders of Maguey and Capulin trees, and a number of wild plants both within and around the crop area. Photo by M.A.Altieri.
OCR for page 380
BioDiversity and other methods. The completely engineered wood grass system includes planting and harvesting. For some countries that do not have mechanized agriculture, these activities will most likely be handled manually. In mechanized agriculture, manure spreaders have been effectively used to spread cuttings and tractors have been fitted with specially made sickle bars for use in harvesting. Good-quality and low-cost structural building material can be made from wood grass by extrusion. In this process, the fresh lignin embodied in the wood grass is used as a primary binder. The term wood grass 2×4 is applied to the product and is used generically to refer to the extruded structural material. The shape of the die can be designed so that a variety of irregular cross-section shapes can be made in different sizes. Wood grass 2×4 utilizes the original molecular structure of wood and fuses the boundaries of adjacent wood grass. This structural material resists bending and twisting, since all joints between adjacent pieces of wood grass need to be broken before such movements are possible. Furthermore, since the extrusion process works better with thin trees and fresh lignin, 1-year-old wood grass is ideal as its feedstock. Figure 43–1 shows the feedstock applications of wood grass. In addition to wood grass 2×4, products include liquid hydrocarbons, alcohols, other chemical feedstocks, and protein. The energy products include heat, electricity, low- and medium-Btu gas, pipeline gas, and liquid fuels. The wood grass production system also stabilizes soil—a tremendous implication for erosion control and watershed management in many countries. The biological foundation of the wood grass production system is shown in Figure 43–2. The right-hand curve indicates growth on a typical plantation planted with a certain number of trees (N) per hectare. The tree is a fast-growing species and has a narrow growth curve, which is characterized by three distinct phases: an initial establishment period in which the trees are developing their root structures; a growth period in which the established trees undergo steady growth—a period recognized by an almost constant rate of growth; and a period in which the growth rate declines as a result of competition for sunlight and nutrients. This third phase is known as closure. A point near inflection of the growth curve indicates the onset of closure. During closure, competition for sunlight and nutrients begins to result in a decreased mean annual increment of biomass. After the onset of closure, not only is the growth rate of each individual tree affected but the average mortality also increases. In this chapter, the term closure is used to encompass all the phenomena that affect the total biomass yield per hectare. The onset of closure is defined quantitatively as the point before which the total quantity of biomass in a given area is proportional to the number of trees in that area. The left-hand curve in Figure 43–2 shows the growth curve if twice the number of trees (2N) are planted per hectare. Initially, the quantity of biomass from 2N trees is almost twice that from N trees, but closure begins earlier. Because of the limits on the ultimate productivity of the land, the maximum quantity of biomass produced from 2N trees appears to be similar to that achieved from N trees after total closure.
OCR for page 381
BioDiversity FIGURE 43–1 Feedstock applications of dry and wet Dushen and direct extrusion applications of wood grass.
OCR for page 382
BioDiversity Two observations can be made from Figure 43–2. First, closure begins sooner if tree density is increased. Second, the limit on the quantity of biomass that can be obtained can be ascertained from a growth curve for any density, provided N is not so low that closure does not take place. The implications of these observations are that the mean annual increment of biomass at harvest can be enhanced by increasing the planting density and that there is an optimal planting density for each rotation (age of trees at harvest), which can be determined. For a short-rotation forest, the optimal harvesting time is some time before the onset of closure. The exact economically optimal harvesting time is a function of the discount rate, which determines the cost of money. Higher discount rates tend to favor an earlier harvesting age, since the value of future harvests is markedly reduced. The decision to grow a particular tree as a crop can be hindered by many considerations. For example, tree growers usually cannot realize their revenue until several (or many) years after planting, and harvested forest land is expensive to clear. Thus, the use of land for wood production involves a long-term commitment. With the current analysis, however, appropriate planting density and production methods can be engineered and trees need not have these disadvantages. Figure 43–3 shows the results of an experiment involving determination of the closure age of trees as a function of the number of trees planted (see Shen et al., 1984). As shown in the figure, if you want to harvest trees after 4 years to obtain a sufficiently large diameter, the planting density is about 1,700 trees per hectare. If you are harvesting every 3 years, you probably want to plant 6,000 to 7,400 trees. And if you are hoping to harvest every 2 years, you need a minimum of 25,000 trees. For an annual harvest, the planting density could be as high as 120,000 trees. And that’s approaching the density of corn or rice. The actual planting density should be based on two considerations. If one is not concerned about committing the land to trees, one could start with about one tree per thousand square centimeters. After the first cutting, the coppice ratio (the number of new stems per old stem) in the second spring could be around 5 to 1. And after the second cutting, the coppice ratio could be around 3 to 1. And the ratio approaches 1 to 1 after that. The desired steady-state wood grass density may FIGURE 43–2 The onset of closure as a function of planting density for a typical plantation.
OCR for page 383
BioDiversity FIGURE 43–3 Closure age as a function of planting density in a forest located in the Great Lakes region of the United States. thus be achieved after two or three cuttings. But by then the root system may be too large to be conveniently plowed under. If one is concerned about crop flexibility, the initial planting density should be chosen to control the size of the root system as well. Wood grass production involves a degree of management as high as that in land consumption activities such as those found in urban areas or in association with roads, mining, and water impoundments. Wood grass is part of modern agriculture, except that in addition to its food and feed products, it produces energy and materials as well. Figure 43–4 shows wood grass grown at a density of one per thousand square centimeters for feed, electricity, and steam. To determine the economics of wood grass production, we analyzed a plantation of wood grass (Populus) in the Pacific Northwest of the United States, allowing a range of uncertainties in the wood grass yield. The cost to produce the Dushen as a function of the discount rate (the cost of money) was estimated. At a 7% real interest rate, for instance, the range of uncertainties is from $12.00 to $25.00 per dry ton. At that rate, the average wood cost is $18.00 per ton, which is $1.00 per million Btu measured in energy value (Jones and Shen, 1982; Shen 1983; Shen et al., 1982; Vyas and Shen, 1982). Which areas are best for growing wood grass? In the United States, the states bordering the five Great Lakes, the Eastern United States, and the Pacific North-
OCR for page 384
BioDiversity FIGURE 43–4 Wood grass in Livingston, California, grown as a low-cost source of protein for poultry feed and as a biomass fuel for cogeneration. Photo courtesy of Foster Farms. west all have excellent soil and climate to support the wood grass production system. At the lower bound of the yield, wood grass competes economically in the Corn Belt at current prices. Its most important role, however, is its potential use in energy, materials, and feed markets of the world. Due to differences in agricultural systems and practices and in topographical and climatic conditions, there are different schemes for producing Dushen feedstock using the wood grass production system. There are also considerations concerning capital versus labor intensity and availability. These can be illustrated by comparing Dushen production in two countries: the United States and China. Field preparation is mostly mechanical in both the United States and China. Planting is mechanical in the United States and manual in China. Figure 43–5 shows farmers planting wood grass at a density of four per thousand square centimeters in Southern China. In both countries, the cuttings are planted vertically or are placed horizontally on the ground and covered with a moisture-preserving mulch such as wheat straw. A manure spreader has proved effective in random horizontal planting. Vertical planting is used for rice seedlings or tree cuttings. Each cutting may produce more than one tree, depending on how many buds are present on the cutting and on the survival rate. The herbicide and fertilizer applications are mostly mechanical
OCR for page 385
BioDiversity in the United States and manual in China. Both countries use chemicals and manure as fertilizer, but the Chinese use more manure, whereas chemicals predominate in the United States. Harvesting is mechanical in the United States and is still manual in China. The Dushen harvester chops wood grass directly into 2.5-centimeter pieces, the wet Dushen. The dry Dushen is produced if the wood grass is crushed with rollers before it is chopped in the harvesting process. A single harvester is needed to produce the Dushen. The near-term uses of wood grass in the United States are heating, animal feed, industrial fuel, the coproduction of steam and electricity, and, most importantly, structural material—material that does not require 50 to 100 years of growing, such as pine trees. The mid-term applications include pipeline-quality gas production, which the Gas Research Institute (GRI) is developing, and liquid fuels. In his work on pipeline-quality gas performed for GRI, David Chynoweth of the University of Florida has found that wet Dushen approaches the performance of the most digestible cellulosic samples used as reference in his experiment. The long-term applications include its use as chemical feedstock, which has the highest market value. In China, the regions of most intensive applications are located in the Northeast, where there is need for industrial fuel and heating, in Eastern China, and in Northwestern China. The near-term applications are cooking, heating, industrial FIGURE 43–5 Establishment of a wood grass multipurpose plot in Fujian Province of Southern China. Chicken manure diluted with rice hull is used as fertilizer. The wood grass will be used as cattle feed. Photo courtesy of Yangting Farm.
OCR for page 386
BioDiversity fuel, cogeneration, animal feed, and construction materials. As in the United States, its long-term use is as chemical feedstock. There are tremendous possibilities here for the production of various materials, including building material, animal feed, and chemical feedstock. At present, the Dushen products from the wood grass production system look attractive because of the system’s rapid return on investment. In the long run, the soil conservation characteristics of the production system may be the most important benefit of wood grass. We recently analyzed the impact of large-scale production in the United States and found wood grass to be a significant soil-conserving crop (Shen and Turhollow, 1983). In contrast to conventional food crops, the wood grass system provides surface coverage throughout the year. In addition, the root system provides a soil-stabilizing matrix. Furthermore, selected wood grass configurations reduce groundwater runoff, increase groundwater infiltration, and recharge groundwater reservoirs. In designing the wood grass production system, we first applied traditional genetic selection to hybrid trees, which were cloned for a number of attributes. We focused on a narrow growth curve and a rapid closure phase. The average growth curves of course are those under selected fertilization and other soil amendment schedules for a specific species-site match. For all clones selected for these two attributes, the coppice growth curves are examined, since sustained steady-state coppice growth is our objective function. In the next step, the selection criteria include disease resistance, drought resistance, and ease of establishment. Then, depending on the desired market, additional attributes directly related to product properties are identified. In practice, this last step is performed at a very early stage for general screening, because the objective of the biological engineering is really the product. On the other hand, without the growth attributes established in the genetic selection, the biological system has no basis. Through the wood grass production system, we have shown that biological engineering with components based on genetic selection, species propagation techniques, modern agriculture, and chemical or mechanical processing methods could produce energy and novel materials that fit within the framework of the existing market infrastructure. This applied engineering approach will allow multidisciplinary teams to produce products and technologies that can be marketed more rapidly than most new technology, while taking environmental benefits into full consideration as a primary long-term objective. CONTOUR HEDGEROWS Contour hedgerows proposed for the highland regions of Nepal, Pakistan, India, and other countries (Benge, 1984) constitute a biologically engineered system for the production of reforestation planting stock. The Department of Soil and Water Conservation of Nepal estimates that between 30 and 75 tons of soil are washed away annually from each hectare of deforested land. This means that Nepal altogether loses as much as 249 million cubic meters of soil per year to India (Cool, 1980). The contour hedgerows alleviate the problem of the short supply of appropriate planting stock, and at the same time effectively check erosion, reduce
OCR for page 387
BioDiversity FIGURE 43–6 Cross-sectional view of hedgerows. groundwater runoff, increase ground water infiltration, recharge groundwater reservoirs, and produce the by-products of fuelwood and fodder. A typical design of a clonal hedgerow system entails the construction of hillside ditches and the planting of two rows of trees or shrubs on the rise (bund) of the ditches, which follow the contour of the hillsides, and one row planted in the depression (Figure 43–6). The hillside ditches increase the system’s effectiveness in controlling erosion while increasing water percolation into the soil. Soil erosion control is more effective when the spacing of the plants is alternated between hedgerows (Figure 43–7). Soil could still be eroded from around the stems. It is desirable to place some type of biomass uphill and behind the live stems to make a more effective barrier to hold the soil and accelerate the formation of natural terraces. Rows of plants on the rise and in the ditch would provide greater access to the forage by browsing animals, if the functions of plant material production and the cut-and-carry system of forage production were phased into a browse-pasture system. FIGURE 43–7 The spacing of plants is alternated between hedgerows.
OCR for page 388
BioDiversity According to Benge (1984), 1 hectare of contour hedgerows could provide enough plant material to reforest approximately 600 hectares (at a spacing of 4 meters between trees) the first year and 3,000 hectares the second year. To arrive at this production figure, a 6-centimeter in-row spacing of cuttings, a distance between rows of 0.5 meter and 0.75 meter, respectively (center to center—3 rows), and a spacing between hedgerows of 5 meters (edge to edge) was used (Figure 43–8). The production capacity of this contour hedgerow system used for clonal propagation of planting stock could be as high as 450,000 cuttings per hectare per year. The actual per-hectare production rate for cuttings from contour hedgerows depends upon the genetic capacity of the clones as well as the environmental conditions in which they are grown. The system benefits from high in-row density and edge effect, i.e., plants near the edge of each hedgerow benefit from additional sunlight and nutrients outside the hedgerow. It is important to incorporate genetic diversity in contour hedgerow systems that cover large areas by the use of a wide variety of species or provenances in order to decrease the possibility of widespread disease and insect infestations and the production losses that would result. Many tree species that have been propagated from cuttings either will not develop a tap root or will develop a modified tap root with extensive lateral roots but without deep penetration into the subsoil. Therefore, these trees will draw nutrients only from the upper soil strata, which may already be nutrient poor from the mining effect of many food crops and other surface feeding plants. Thus, it may be desirable to plant between the contour hedgerows trees that have been propagated from seeds and that develop a deeper tap root system (Figure 43–8). This would increase the per-hectare productivity of the FIGURE 43–8 Complete biologically engineered system of contour hedgerows.
OCR for page 389
BioDiversity system, since these trees would pump from a deeper soil strata nutrients that may not be available in the shallower soil. REFERENCES Benge, M.D. 1984. Contour hedgerows for soil erosion control and planting stock, forage and fuelwood production in highland regions. Pp. 117–123 in Energy from Biomass: Building on a Generic Technology Base. Proceedings of the Second Technical Review Meeting. Report No. ANL/CNSV-TM-146. Argonne National Laboratory, Argonne, Ill. Cool, J.C. 1980. Stability and Survival—The Himalayan Challenge. Ford Foundation, New York. 22 pp. Jones, P.C., and S.Y.Shen. 1982. A Framework for Evaluating the Economics of Short-Rotation Forestry Research and Development. Report No. ANL/CNSV-35. Argonne National Laboratory, Argonne, Ill. 56 pp. Shen, S.Y. 1982. Wood Grass Production Systems for Biomass. Paper presented at the 1982 Midwest Forest Economist Meeting, Duluth, Minn., August 17–19, 1982. Shen, S.Y. 1983. Regional Economic Impacts of Woody and Herbaceous Biomass Production. Paper presented at the 1983 Joint National Meeting of the Institute of Management Science and the Operations Research Society of America, Chicago, April 24–27, 1983. Shen, S.Y., and A.F.Turhollow. 1983. Regional impacts of herbaceous and woody biomass production on U.S. agriculture. Pp. 207–234 in Symposium Papers: Energy from Biomass and Wastes VII. Presented January 24–28, 1983, Lake Buena Vista, Fla. Institute of Gas Technology, Chicago. Shen, S.Y., P.C.Jones, and A.D.Vyas. 1982. Economic Analysis of Short-Rotation Forestry. Paper presented at the 1982 Joint National Meeting of the Operations Research Society of America and the Institute of Management Sciences, San Diego, Calif. October 1982. Shen, S.Y., A.D.Vyas, and P.C.Jones. 1984. Economic analysis of short and ultra-short rotation forestry. Resour. Conserv. 10:255–270. Vyas, A.D., and S.Y.Shen. 1982. Analysis of Short-Rotation Forests Using the Argonne Model for Selecting Economic Strategy (MOSES). Report No. ANL/CNSV-36. Argonne National Laboratory, Argonne, Ill. 50 pp.
OCR for page 390
BioDiversity This page intentionally left blank.
Representative terms from entire chapter: