Percepción de sí, del -otro- y la existencia

more than 10 people/km ² , easily 100 times as many as could be supported in the same environments with foraging. This transition to more intensive modes of food procurement was a matter of complex evolution, and any notion of agricultural revolution (Childe 1951) is an indefensible intellectual construct. For example, wild cereals were collected and processed and the resulting fl our was used in baking in Israel during the Upper Paleolithic (19,500 BCE), at least 12,000 years before the domestication of cereals (Piperno et al. 2004). In contrast, Mexico ’ s Tehuac á n Valley had no permanent settlements but thousands of years of crop cultivation (Bray 1977), and many settled agricultural societies retained signifi cant elements of forag-ing for millennia. Clearly, there was no orderly lock-step progression of cultivation and sedentism, no sharp divide between foraging and incipient cultivation.

The cumulative impact of animal domestication and shifting and permanent crop cultivation began to transform ecosystems not only on local or small regional scales but eventually across large areas of some key biomes. As already noted, Ruddiman (2005) has argued that humans actually took control of the climate For centuries, rice has been the world ’ s most important staple grain crop. This photograph shows the mechanized harvesting and drying of sheaves on wooden supports in a fi eld near Ky o¯ t o¯ in the early 1990s. Photograph by V. Smil.

Crops and Animals 105

Table 8.1

Density of Human Populations

Population Density

(people/km ² ) Live Weight (kg/ha)

Foraging 0.01 – > 1 0.005 – 0.5

Pastoralism 1 – 2 0.5 – 1

Shifting cultivation 20 – 30 9 – 14

Traditional farming

Predynastic Egypt 100 – 110 45 – 50

Medieval England 150 75

Global mean in 1900 200 100

Chinese mean in 1900 400 180

Modern agriculture

Global mean in 2000 400 200

Chinese mean in 2000 900 410

Jiangsu province in 2000 1,400 630

Note: All densities for foragers and pastoralists are per unit of exploited of land; all densities for traditional and modern agriculture are per unit of arable land.

through these actions. That conclusion is debatable, but there can be no doubt about the large-scale and often lasting environmental transformations brought about by pastoralism and cropping. And these changes affected not only fertile river valleys, coastal lowlands, or forests near growing population centers but even Amazonia, a region that was considered until recently the very epitome of undis-turbed nature.

The transition to permanent cropping involved a complex mix of natural and social factors. The climate was too cold and CO 2 levels were too low during the late Paleolithic, but the subsequent warming, as Richerson, Boyd, and Bettinger (2001) put it, made agriculture mandatory in the Neolithic. After all, between 10,000 and 5,000 years before the present, agriculture had evolved independently in at least seven locations on three continents (Armelagos and Harper 2005). At the same time, the importance of cultural factors is undeniable, as sedentary farming fostered association and more complex social relations, promoted individual owner-ship and the accumulation of material possessions, and made both defense and aggression easier — but Orme (1977) went too far when he argued that food produc-tion as an end in itself may have been relatively unimportant.

Traditional low-yield cropping was the dominant subsistence mode in all prein-dustrial societies. Its practice shared some notable universal commonalities: grains

as principal staple crops in all extratropical climates, the rotation of cereals and legumes, cattle used predominantly as draft animals rather than as sources of meat.

But there were also many unique cropping sequences, some involving rotations of more than a dozen crops; differences in the domestication of animals (dairying cultures vs. societies abstaining from milk consumption); and distinct diets. Even the least intensive forms of cropping were able to support more than 100 people/

km ² , and the best Asian and European practices could feed more than 500 people/

km ² , that is, more than 5 people/ha (Smil 2008; table 8.1 ).

But even the best traditional productivities did not suffi ce to meet the post-1850 food demand driven by expanding populations, rapid rates of industrialization and urbanization, and higher incomes. Modern high-yield cropping has been a recent creation: its beginnings go back only to the last decades of the nineteenth century and its greatest returns have come only since the 1950s. Superior new cultivars can take advantage of new agronomic practices that combine high rates of fertilization, applications of herbicides and pesticides, supplementary irrigation, and the near total mechanization of fi eld and processing tasks and that can provide excellent diets by supporting more than 10 people/ha. Moreover, these practices take advan-tage of comparative environmental advanadvan-tages and increase the shares of national diets coming from imports (it is not uncommon to import more than 20% of all food energy). They also made it possible to consume unprecedented amounts of animal foods.

Shifting Cultivation and Pastoralism

Dissimilar as they appear to be, these two most extensive ways of food production are both suited only for low population densities because they both share an inter-mittent use of land. Shifting cultivation (swidden or slash-and-burn farming) and pastoralism could be also seen as intermediate evolutionary steps between foraging and permanent sedentary farming: they share extensive land use with the former but orderly practices (regular planting of crops, seasonal use of best pastures) with the latter. Of course, their environments differ greatly: shifting agriculture is best suited for forests and woodlands, while animal grazing converts grassy phytomass (indigestible by humans) to high-quality animal foods (milk, blood, meat) and hence enables people to survive in regions too arid for regular cropping.

As a result, the population densities of some nomadic pastoralists were as low as those of gatherers and hunters, while shifting agriculture could support popula-tion densities an order of magnitude higher than even the relatively best-off

(seden-Crops and Animals 107

tary maritime) foraging societies. But these extensive food production ways shared yet another important commonality: in areas with low population densities they proved to be extremely long-lived and resilient to change, while in other regions they gradually morphed into various combinations of shifting and permanent farming, or what might be best called seminomadic agropastoralism with some foraging still present. Rising population densities brought a rather rapid end to these modes of subsistence, mainly because of shorter soil regeneration cycles in shifting cultivation and the overgrazing of many pastures.

Shifting cultivation begins by removing natural vegetation (preferably a second-ary growth, which is usually easier to clear away than a primsecond-ary forest), often by burning or (once better tools became available) by felling large trees fi rst and then slashing younger growth before setting woody piles afi re, or simply by slashing a secondary growth without burning. The resulting patches ranged from fairly level surfaces that were often turned into densely planted gardenlike plots (interplanting and multilayered polycultures were common) to roughly surfaced small fi elds con-taining remnants of large burned trees where crops were grown in mounds or clumps. Regardless of the clearing method, shifting cultivation shared the underlying strategy of exploiting the nutrients accumulated in plants and soil.

Phytomass burning recycles all mineral nutrients (K, Ca, Mg), and while nearly all nitrogen in the burned phytomass is lost to the atmosphere as NO x , a great deal of this key macronutrient remains in soil, and additional supply comes from the mineralization of decaying (slashed or uprooted) vegetation, so that crops can be grown for a few seasons without any other nutrient inputs. The staples of shifting cultivation included grains (rice, corn, millet), roots (sweet potatoes, cassava, yams), and squashes and various legumes (beans, peanuts), and the most diverse plantings included one or even two scores of edible, fi brous, and medicinal plants. Such plots required a considerable amount of maintenance (weeding, hoeing, pruning, thin-ning), and they also needed guarding or fencing, while many fi elds with staple crops were left in a semiwild state (subject to considerable damage by pests and animals) until the harvest.

Relatively large areas of forest were needed in places where just one or two years of cultivation were followed by long regeneration periods of more than 10 and even as many as 60 years; more intensive cultivation with a few crop years followed by only slightly longer (4 – 6 years) fallow periods were eventually quite common, and in many locations higher population densities compressed the cycle to the shortest fallow spans possible, with a crop or two followed by a single year of regeneration.

Australia was the only continent where this practice was never important, while in

large parts of Asia, Africa, and the Americas it not only preceded permanent crop-ping but has also coexisted with it, often literally side by side. Shifting cultivation was not only the foundation of ancient Mesoamerican cultures, it left its mark on relatively large areas of the Amazon.

Those regions are readily identifi ed by their soils: terra preta (or, more precisely, terra preta do í ndio ) can be up to 2 m deep; it contains relatively large amount of charred phytomass residues as well as elevated levels of organic matter from crop residues, human waste and bones (often in excess of 13% of total organic matter, that is, more than 5% C); and it was created by centuries of shifting cultivation, mostly between 500 BCE and 1000 CE (Glaser 2007; Junqueira, Shepard, and Clement 2010). Lehmann et al. (2003) estimated that terra preta soils cover no more than 0.3% of the low-lying parts of the Amazon basin, but other estimates are up to an order of magnitude higher.

In Asia, permanently cropped valleys and shifting cultivation in neighboring hills and mountains have coexisted for millennia, and in the southeastern part of the continent the forest clearing for cultivation has survived into the twenty-fi rst century (Allan 1965; Watters 1971; Okigbo 1984). Swidden cultivation was also common in the temperate and boreal zones of preindustrial North America: Canada ’ s Hurons were among the northernmost practitioners, cultivating corn and beans for at least 5 and up to 12 years before clearing a new patch of forest and letting the land regenerate for 35 – 60 years (Heidenreich 1971). With a typical corn harvest of 1.5 t/ha and a 50-year rotation cycle, they could support between 10 and 20 people/ha.

Shifting cultivation was not uncommon in medieval Europe — even in the Î le-de-France region around Paris it was practiced until the early twelfth century (Duby 1968) — and it survived in parts of Central and northern Europe and Siberia not only into the nineteenth but even to the middle of the twentieth century. In Ger-many ’ s Ruhrgebiet, tree fallows (harvested for bark and charcoal) alternated with rye until the 1860s (Darby 1956); rye was also used in Siberian shifting cultivation until the 1930s; and in Finland of the late 1940s birch and pines (cut and sold as logs) were followed by alder, whose burning prepared the soil for turnips. Other crops used in European shifting cultivation in Scandinavia, Central and Eastern Europe, and northern Russia (in some cases until the 1950s) included barley, fl ax, millet, oats, and wheat, and fallow periods in the sub-Arctic forests were as long as 40 years.

Net energy returns of shifting cultivation (quotients of harvested edible phyto-mass and energy consumption above basal metabolism) are as low as six- to tenfold and as high as 20- to 30-fold in various tropical environments, with rates between

Crops and Animals 109

15 and 20 being perhaps the most common and with maxima above 50 for some crops (Smil 2008). Average per capita requirements for shifting cultivation range from as much as 10 to less than 2 ha of land in fallow and under the crops, and the area actually cultivated is most commonly between 5% and 20% of those totals.

This translates to population densities as low as 10/km ² and mostly between 20 and 40/km ² , or an order of magnitude above the rates of 1 – 2/km ² typical of pastoral societies.

Specifi c claims made by shifting cultivation on the biosphere ’ s phytomass vary widely, with the difference due mainly to the kind of cleared vegetation and to the length of the fallow period. Short fallows of less than fi ve years, removal of relatively thin secondary (or later) growth, and a single year of cropping may claim only a small fraction of phytomass that is destroyed by burning primary growth, followed by a longer (more than 10 years) fallow period. Detailed monitoring of a Javanese short-rotation system — one year of mixed vegetables followed by a year of cassava followed by four years of bamboo fallow — showed the importance of the regenera-tive period: at its end, organic matter in the top 25 cm of soil had increased by about 7 t/ha, an outcome well justifying a traditional saying that “ without bamboo, the land dies ” (Christanty, Mailly, and Kimmins 1996). Two specifi c examples based on data obtained by fi eld studies illustrate the overall impact of short- and long-rotation practices ( box 8.1 ).

Even if the population densities supportable by shifting cultivation were to cluster rather tightly around 20 – 30 people/km ² and even if we knew approximate totals of people engaged in these practices in the past, we still could not calculate the overall claims on the biosphere because the standing phytomass destroyed by felling or slashing and burning can vary by a factor of four. Shifting cultivation still survives in some tropical and subtropical regions, and some of its practitioners — including the Hanunoo of the Philippines (Conklin 1957), the Kekchi Maya of Guatemala (Carter 1969), the Tsembaga of New Guinea (Rappaport 1968), the Yukpa of Colombia (Ruddle1974), the Iban of Sarawak (Freeman 1980), the Kantu ’ of Kalimantan (Dove 1985), and the swidden cultivators of India ’ s Manipur state (Shah 2005) and China ’ s Yunnan province (Yin 2001) — were studied in considerable detail by modern anthropologists.

Perhaps the most revealing conclusion is that they found fairly similar and rela-tively high net energy returns (the quotient of the food energy in harvested crops and the energy spent in their cultivation) ranging between 15 and 25. But McGrath (1987) correctly pointed out that what has traditionally been seen as a highly pro-ductive system when assessed in terms of energy outputs and inputs is really an

Box 8.1

Shifting Cultivation: Phytomass Removal and Harvests

In Central America milpa , a plot of land devoted to the shifting cultivation of corn supplemented by half a dozen (interplanted and planted in sequence) fruit and vege-table species, is managed by a short cycle of four years of forest fallow and one year of crops (Carter 1969). An average corn yield of just over 1 t/ha (15 GJ/t) means that (assuming a 20% preharvest loss to wild animals and pests) the edible yield is about 11 GJ/ha planted. The short rotation entails clearing relatively thin secondary growth;

even if it stores no more than 50 t/ha or (at 16 GJ/t of dry matter and a 90% removal rate after slashing and burning), the total is about 2.9 TJ of woody phytomass from the four fallowed hectares. More than 99.5% of the total phytomass removed from the site on a fi ve-year fallow/crop cycle is thus the cleared woody matter, and with an average annual food requirement of about 10 GJ per capita, this cultivation will need about 4.5 ha per person, supporting about 20 people/km ² .

A very different shifting cultivation was studied by Rappaport (1968) in New Guinea: a long (15-year) fallow and a highly productive two-year gardenlike polycul-ture of more than 20 root (taro, yam, cassava), vegetable, and fruit species. The planted area is thus only about 12% of all managed land, and with forest phytomass stores at 150 t/ha and an 80% removal rate, every cycle would destroy 1,800 t of woody matter, or about 29 TJ. Even if the annual edible harvests were as high as 25 GJ/ha, in two years they would still amount to less than 0.2% of all the phytomass removed from the affected land during the 17 years of a fallow/crop cycle. With annual food require-ments at 10 GJ per capita, this shifting cultivation would need nearly 3.5 ha of fallow and gardens per person and could support nearly 30 people/km ² .

extremely unproductive practice once the total phytomass contributions are taken into account. And the studies encountered a variety of location-specifi c practices, which does not make for any easy quantifi cation of typical impacts.

Most recently, a global project on alternatives to slash-and-burn cultivation quantifi ed a wide range of possible carbon stock changes (Palm et al. 2004). While undisturbed tropical forests averaged 300 t C/ha and managed and logged forests stored mostly between 150 and 250 t C/ha, short fallow (4 – 5 years), shifting culti-vation replaced them with vegetation storing no more than 5 – 10 t C/ha — but long fallow (more than 20 years) and more complex alternatives (including agroforestry and intensive tree crops) could store an order of magnitude more of phytomass, between 50 and 100 t C/ha. Interestingly, the latest studies of shifting agricultures in Southeast Asia, the region with the highest remaining concentration of such farmers, have been reappraising the practice at a time when it is rapidly receding (Padoch et al. 2008).

Crops and Animals 111

Besides fi nding a surprising lack of agreement on the actual extent of the practice throughout the region, most of these studies document the replacement of shifting cultivation either by other forms of agriculture or silviculture (rubber or fruit trees, oil palms, plantation timber), as well as decreases in fallow length (Schmidt-Vogt et al. 2009). They stress its rationality in many tropical mountain environments, its suitability for smallholder operations, and, if properly practiced, its relatively high productivity. Moreover, case studies in Malaysia and Indonesia show that fallow length is a very weak predictor of subsequent yields and other factors (above all droughts, fl oods, and pests) are much more important (Mertz et al. 2008). Studies of vegetation recovery in northwestern Vietnam have demonstrated that the effect on biodiversity may not be as damaging as has been usually thought: after 26 years a secondary growth had half the species of the old-growth forest, and it was esti-mated that it would eventually reach a similar plant species diversity and about 80% of the original biomass (Do, Osawa, and Thang 2010).

Generalizations concerning pastoralism — which entails the metabolic conversion of grassy phytomass into meat, blood, and milk (and also wool and hides) through animal grazing — and fairly reliable summations of its worldwide claim on biomass are no less elusive. Pastoralism is perhaps best defi ned as a form of prey conserva-tion whereby deferred harvests are profi tably repaid by growing stocks of zoomass (Alvard and Kuznar 2001). This trade-off is more profi table for larger animals, but it is not surprising that the smaller species, sheep and goats, were domesticated fi rst, because they have higher growth rates and are less risky to manage. The earliest domesticated animals — leaving dogs aside (Pang et al. 2009) — were sheep: their domestication process began about 11,000 years ago in Southwest Asia, and it was followed by goats and cattle (86,000 BCE), and later horses and water buffaloes (4000 BCE); domesticated pigs have been around nearly as long as sheep, chicken only about half that time (Ryder 1983; Harris 1996; Chessa et al. 2009).

Agropastoralism eventually became the dominant way of food production through-out Europe, North Africa, and West and Central Asia. Traditional pastoralist prac-tices were strictly exploitative: there was no improvement of natural pastures, and labor (a signifi cant share of it provided by children) was confi ned to herding (with a single person often responsible for hundreds of cattle and even larger herds of sheep or goats), guarding (sometime including the construction of temporary enclo-sures), and watering the animals. As a result, the ecological effi ciency of pastoral subsistence — the quotient of the food energy of animal tissues consumed by humans and the forage energy intake of animals — was mostly less than 1% in seasonally

arid African environments, similar to the effi ciency of food obtained from hunting large native ungulates (Coughenour et al. 1985).

Milk and blood rather than meat were the primary food products (only old and ill animals were slaughtered). The variety of environmental settings (from poor semideserts to tall tropical grasses) and of domesticated herbivores precludes any easy generalizations about typical population densities of pastoral societies, whose

Milk and blood rather than meat were the primary food products (only old and ill animals were slaughtered). The variety of environmental settings (from poor semideserts to tall tropical grasses) and of domesticated herbivores precludes any easy generalizations about typical population densities of pastoral societies, whose