By Gerald W. Olson
Archeological records contain advice aplenty for modern man and his use of the land
The past is a key to the future (6). Archaeological strata contain artifacts that record events and processes during millennia of human occupations of different soils. In many areas, contemporary use of soils is not greatly different from ancient use of soils. In other places, technology has changed a great deal, but always the soils in landscapes have a dominant influence upon land use patterns. Often, the archaeological record proves that ancient people abused their soils, and their civilizations were disrupted by the ecological and environmental consequences. In places, ancient populations were larger than modern populations.
Archaeological considerations give reason for modern man to ponder if he is using resources wisely and to seek explanations for the ancient population declines and shifts so that he might avoid a similar fate. Generally, the most important factors in a nation's continuing prosperity are not its conquests in war (1) but the nature of its husbandry of soils through centuries of use and occupation.
Extensive research on relations of soils to archaeology has been done in Maya areas of Central America. At Tikal in the Peten region of Guatemala, soils were described, sampled, and mapped at a scale of 1:2,000 (5). The Maya apparently achieved good mastery of the visible soil properties related to engineering use and management through experience more than 2,000 years ago. Invisible and less visible degenerative soil processes (soil fertility depletion and erosion), however, caused many insidious long-run problems for the Maya. The soil survey of Tikal is a good example to look at in detail and to generalize from because it is the most detailed (large-scale), comprehensive soil survey ever conducted specifically for soils and archaeological correlations in the Maya areas.
At Tikal, Mollisols, Vertisols, Inceptisols, Entisols, and various other soils were discovered in the central core of the abandoned Maya city. The bajo swamps had Vertisols with soil properties extremely poor for heavy urban constructions. The Maya avoided these areas for their buildings. In contrast, the Mollisols shallow to limestone bedrock afforded excellent sites for heavy limestone buildings.
Mollisols of the uplands at Tikal were naturally fertile but extremely vulnerable to erosion and damage by Maya populations because of the shallowness of the soil to limestone bedrock. The dark Mollisol appearance of the thin surface soil formation misled the Maya settlers. The topsoil was quickly oxidized and depleted by erosion when the forest was cleared. As the Maya population expanded, erosion and soil depletion accelerated until the "tragedy of the commons" (3) produced excessive deterioration of the soil resources.
In disturbed areas, including causeways and built-up areas, light-colored Inceptisols and Entisols were mapped that were distinctly different from the dark-colored, undisturbed Mollisols. Disturbed areas in the uplands of Tikal could be located and mapped in the silt loam places based on soil color alone. Light soils were depleted. Dark soils were nutrient-rich. Soils at Tikal have not recovered from the Maya occupation, even after more than 1,000 years of abandonment to the rain forest.
Maize on the Mollisols at Tikal (in few patches tilled at present by shifting cultivation) yields about 1,000 kilograms per hectare in the first year after clearing, about 750 kilograms in the second year, about 500 kilograms in the third year, and about 250 kilograms in the fourth year--without any fertilizer. For shifting cultivation, the Food and Agriculture Organization of the United Nations officially recommends a 15-year rotation on these soils--where an area cleared from the forest is cropped for 5 years, then left fallow for 10 vears for forest regrowth before clearing the area again for cropping.
Obviously, the Maya could not have maintained this ideal rotation as their population increased, and the consequent soil decline had a considerable influence on the culture during the centuries of Maya occupation. The important but gradual soil changes taking place probably went almost unnoticed by the Maya, owing to the slow, insidious nature of soil erosion and nutrient depletion. Large amounts of eroded sediments were deposited in drainageways and reservoirs. Sedimentation from soil erosion had a highly detrimental effect upon the limited water supply in the urban setting.
Among the evidence that excessive soil erosion is detrimental to everyone is a buried soil profile that was farmed by the Maya in the Valle de Naco in Honduras more than 1,000 years ago (6). As the Maya population expanded into the hills around the valley site, forests were cleared in the uplands and soil erosion accelerated greatly. Eventually, excessive erosion caused flooding in the valley, and yields declined in the uplands. About 1,000 years ago, the civilization collapsed, and its population abruptly declined.
An alluvial streambank cut records some of the events of Maya history. The lower profile, which the Maya used, has artifacts of the period scattered through the soil and accumulations of phosphorus from the human habitations. The upper profile is devoid of artifacts. Apparently, erosion depleted the soil resource base and caused flooding so that production declined to the point that it could no longer support the dense Maya population. When the population declined, the vegetation recovered.
This cycle appears to be repeating with modern land abuse. The present population in the area is probably less than in the Maya period, but it is increasing. The Maya history, recorded in the soils, is a message to be heeded by modern planners and soil conservationists.
In parts of El Salvador, deterioration of Maya soils was caused by active volcanoes as well as soil erosion and nutrient depletion. A series of soil profiles found in different volcanic materials at the Cambio archaeological site northwest of San Salvador all have Maya artifacts in them. One profile includes a contemporary house; an upper infertile soil profile formed mostly in dark, coarse cinders; an indurated tephra layer dated at about 1,000 years; a soil profile formed mostly in white, very fine sand ash dated at about 2,000 years; and a lower fertile clayey soil profile formed in older, more highly weathered reddish material tens of thousands of years old. The surface soil has 4.3 percent organic matter and relatively high levels of nutrients due to tree litter recycling and anthropic accumulations from the modern household, but soil in an eroded field behind the house has only 1.8 percent organic matter and a more acid pH.
This landscape was probably fairly stable from about 40,000 years to 2,000 years before present, so that a fertile soil could develop with good nutrients and excellent water-holding capacity in weathered clayey textures. A volcanic eruption 2,000 years ago covered the area with fine sandy ash in which a much inferior soil formed with relatively low water-holding capacity for plants in the dry season, but the Maya resettled it anyway. Finally, the later deposits of coarse cinders produced an even poorer soil for the later and recent occupation. The effects of erosion and oxidation on the soil surface illustrate well the soil degradation taking place at the present time.
At many locations in Maya areas, observations can be made like that in the Valle de Naco, where erosion and sedimentation of soils are associated with Maya decline and abandonment. Some of these observations have been documented by archaeologists P. D. Harrison and B. L. Turner II (4). Archaeologists digging into Maya mounds in Belize (8), for example, reported:
"In our excavations on the highest river terrace level...we noted that underlying the mounds at a level approximately 1.00 meter beneath the present ground level there was a stratum of black organically stained soil about 70 centimeters thick. This black stratum contrasted with the brown clays above and beneath it and was similar in appearance to the present humus stratum which forms the uppermost soil zone over the site. We noted that mounds whose construction began in Preclassic Period times had their bases directly on or slightly into the black soil stratum, while mounds whose construction began at a later date had sterile brown clay intervening between the mound base and the black soil. It is tempting to ascribe this phenomenon to the following hypothetical explanation.
"When the first Maya settlers arrived along the Belize Valley in Preclassic times, the uppermost terrace was heavily forested. As today, it was rarely, if ever, reached by flood waters, so that a substantial zone of humus, represented by the black soil stratum, could accumulate. When the land was cleared for habitation this humus accumulation was halted. At about the same time as the Belize Valley was being settled, Maya groups were also occupying the limestone country throughout the drainage basin of the river. As settlement of the region became more extensive and population increased, sufficiently large tracts of high forest were felled for agriculture and settlement to effect the moisture-holding and absorbing qualities of the forest cover as a whole. This meant that the rainy season runoff was increased in both quantity and intensity, resulting in more severe flooding downstream along the river. The uppermost river terrace at Barton Ramie now was occasionally flooded, accounting for the sterile alluvial deposit between the old humus zone and the bases of the later mounds. Increased flooding might also account for an apparently increasing tendency for higher house substructures during the later phases of the occupation of the site. After the region was abandoned or nearly abandoned, at the close of the New Town Phase, the forest as well as the river reverted to the conditions which had prevailed prior to the Maya occupation."
Sardis in western Turkey is another large archaeological site that has extensive soils investigations (7). The ruined city, about 75 kilometers east of Izmir, probably was settled first in the third millennium B.C. The city experienced droughts, earthquakes, famines, fires, floods, invasions, landslides, and sieges. It was the capitol of the ancient kingdom of Lydia, the western terminus of the Persian royal road described by Herodotus, a center for administration under the Roman empire, and the metropolis of the province of Lydia in later Byzantine times. A strategic military location, Sardis' position on a main highway between the Anatolian plateau and the Aegean coast and its access to the wide, fertile plain of the Gediz river valley all contributed to its importance.
Sardis was referred to in the Iliad (as Hyde), mentioned by the Greek poet Alcman about 650 B.C., and addressed as one of the Seven Cities of Asia in the Book of Revelation in the Bible. It was captured by the Cimmerians in the seventh century B.C., by the Persians in the sixth century B.C., by the Athenians in the fifth century B.C., and by Antiochus the Great in the third century B.C. It was destroyed by an earthquake in 17 A.D., but was rebuilt under Tiberius. The fort on the Acropolis was handed over to the Turks in 1306. It was captured by Timur in 1402. The latest conflicts at Sardis were battles of the Greco-Turkish war in the first quarter of the twentieth century. Ruins at Sardis have been excavated since 1958 by a Cornell-Harvard expedition.
Soils of Sardis were of special interest in efforts to reconstruct the evolution of the urban community in relation to its environment. Soils were described and sampled according to standard procedures used by the Turkish Soil Survey and the Cooperative Soil Survey of the United States.
In amazing fashion, much of the history of Sardis is reflected in the soils. Most of the soils are Entisols and Inceptisols on steep slopes or in alluvial valleys, affected by landslides, erosion, and alluvial deposition. Soils on upper slopes have been overgrazed by goats and sheep for centuries. Many of the ruins have had their foundations destroyed through the actions of erosion and landslides. Forests originally protected the soils on the mountains, but the trees were cut for building construction and to provide firewood for the Roman baths.
In a sense, the civilizations destroyed themselves because of the ecological and environmental degradation. In one place at Sardis, archaeologists dug a trench 12 meters deep through a Roman dump containing thousands of animal bones. Because of the overgrazing and subsequent soil erosion, Roman engineers were forced to design settling pots at close intervals in certain water lines at Sardis so that soil sediments could be removed periodically. The Lydian occupation seems to have been most affected by flooding, and the most conspicuous landslides followed in the Greek and Roman periods. A stratum at one point had artifacts from 1300 B.C. buried more than 12 meters below the modern soil surface. Although the floods and landslides were disastrous for the inhabitants of Sardis at the time, the deposits of soil materials were a boon to archaeologists because they preserved some of the ruins from further destruction by nature and by human beings.
Many soils at Sardis have large contents of mica flakes, which contribute to sliding, especially when they are wet. The soil structure in these places not only records past soil movements, but also indicates possible directions and magnitudes of future landslides likely to follow major earthquakes.
The splendor of ancient Sardis still evident gives reason to ponder man's own future. Obviously, when the Romans built their huge bath complexes, they did not consider the ecology or sustained yield factors for the forests cut to provide heat for their water baths. Nor did the Greeks comprehend the effeets of their goat herds on soil erosion. For their part, the Lydians overlooked the hazards of building on an alluvial floodplain.
What benefits ean be obtained from evaluation of past civilizations on the soils of Sardis? Experiences at Sardis should emphasize that constructions on floodplains are likely to be damaged by floodwaters and alluvial deposits. Landslides, common to Sardis and many other parts of the world, can be predicted by internal and external soil charaeteristies. Soil erosion, whether at aneient Sardis or in modern urban construction areas, cannot extend over large areas for long periods without causing severe damage to structures and watersheds. The silting of water systems at Sardis was remarkably similar to some of our siltation problems in municipal water reservoirs.
Erosion control is particularly critical for maintenance of soil fertility for food production as well as environmental quality considerations. Guiding human activities toward consideration of ecology and natural soil landscape variations would be a positive step toward assuring that future civilizations will enjoy greater success and persist longer than did past civilizations. Interdisciplinary efforts to better understand the environment and its relationships to the welfare of inhabitants would contribute toward a more optimistic view of the future.
In the Negev desert (2), experiment stations have been established and interdisciplinary teams have conducted investigations into ancient relationships between human beings and the environment. The interdisciplinary teams included geologists, archaeologists, agronomists, engineers, photogrammetrists, soil scientists, and historians. A farm at Avdat was reconstructed near the ancient city of Shivta to demonstrate that the desert environment could be made habitable once again with careful husbandry of the sparse resources.
The Negev has been inhabited for many thousands of years. Paleolithic and Mesolithic peoples (before 11,000 B.C.) were mainly hunters. In the Neolithic (5000-4000 B.C.), the area was well populated, and people lived and farmed in the wadis and loess plains. For about 2,000 years, much of the southern and central Negev was abandoned. Colonization was intense in the Bronze Age (about 2000 B.C.). By 1000 B.C., the Negev was part of the Israelite kingdom. Around the sixth century B.C., the Kingdom of Judah was destroyed by the Babylonians, and Bedouin nomads grazed the Nege with their flocks. From about 300 B.C. to A.D. 600, the Nabatean-Roman-Byzantine cultures occupied the desert, and the area prospered intermittently. Trade flourished in the Byzantine period. Caravan routes were established. But the Arab conquest forced the area once again into decline. Farms and cities were abandoned.
Soils and substrate in the Negev today contain artifacts of all these civilizations and record much of the history of the military conquests and environmental changes at each site.
The soils of the Negev (2) contain evidence that two systems of ancient agriculture--narrow terraced wadis and farm units with small watersheds--represented the most rational and wise use of the available natural resources. The small plots fit into the natural soils landscapes without damaging the environment. When the agricultural systems were expanded into large catchments, however, the expectations were greater than the resources, resulting in "miscalculation leading to erosion, silting up, and destruction because this approach to cultivation of the desert was overambitious.
The agricultural systems are another illustration of the tragedy of the commons (3). When yield expectations were modest, the area flourished. But when yield demands were greater than the soil and water resources of the landscape could bear, the farming system collapsed.
The overgrazing that folowed the destruction of the farming systems in the Negev also provided yet another example of the tragedy of the commons:
"When the Bodouin took over the Negev they mismanaged the desert in another way. They overexploited one of its main natural resources, the idigenous vegetation, by continuous overgrazing. They never made the slightest effort to restore some of the natural pastures which consist of the plant communities of the various desert ecosystems. Consequently plant and animal life deteriorated seriously."(2)
Many more examples exist of the longterm effects of soil abuse as documented in archaeological records. Each archaeological site, of course, is somewhat unique with respect to the soils and geomorphic and anthropic relationships. All sites appear to be somewhat similar, however, in the evidences of erosion, sedimentation, disturbance, depletion, and enrichment remaining in the soils from past human land uses.
All of these observations have implications that should be obvious to modern man in planning for the future. Today, soil maps and resource inventories exist in detail never available to past peoples. Using this inventory information to better manage soils should permit better understanding of archaeological lessons and thus avoid the mistakes of past civilizations.
1. Brown, L. R. 1977, Redefining national security. Paper 14. Worldwatch Inst., Washington, D.C. 46pp
2. Evenari, M., L. Shanan, and N. Tadmor. 1971. The Negev: The challenge of a desert. Harvard Univ. Press, Cambridge, Mass. 345 pp.
3. Hardin, G. 1968. The tragedy of the commons. Science 162: 1,243-48.
4. Harrison, P. D., and B. L. Turner II. 1978. Pre-Hispanic Maya agriculture. Univ. of New Mexico Press, Albuquerque. 414 pp.
5. Olson, G. W. 1977. The soil survey of Tikal. Agron Mimeo. 77-13. Cornell Univ., Ithaca, N.Y. 82 pp.
6. Olson, G. W. 1981. Soils and the environment: A guide to soil surveys and their applications. Chapman and Hall, New York, N.Y. 200 pp.
7. Olson, G. W., and G.M.A. Hanfmann. 1971. Some implications of soils for civilizations. N.Y. Food and Life Sci. Quart. 4: 11-14
8. Willey, G. R. et al. 1965. Prehistoric Maya settlements in the Belize Valley. Papers, Peabody Museum Archaeol. and Ethnol., vol. 54. Harvard Univ., Cambridge, Mass. 589 pp., map.