Terrace farming

Although use of upland areas in Europe is declining there are other regions of the world where mountainsides are used intensively for agriculture, usually due to

Terrace Farming The Mountains

Fig. 11.28 Terraces on the mountain below the Lost Inca City ofMachu Picchu near Cuzco (Peru). The development ofterracing in Andean agriculture reached its peak in the Inca Empire and produced a form of mountain horticulture that has never been surpassed in terms of soil and water conservation. (Photo Barbara Crawford.)

Fig. 11.28 Terraces on the mountain below the Lost Inca City ofMachu Picchu near Cuzco (Peru). The development ofterracing in Andean agriculture reached its peak in the Inca Empire and produced a form of mountain horticulture that has never been surpassed in terms of soil and water conservation. (Photo Barbara Crawford.)

population pressure and a shortage of level land. In highly settled mountainous areas one of the most sophisticated agricultural techniques is the use of terracing. It is often assumed that the terracing has been put in place with the sole purpose of reducing erosion. Terracing as developed in the Andes not only reduces soil erosion but serves also the equally important purpose of maximizing water use by the planted crops (Fig. 11.28). The use of terraces and irrigation for growing crops at high altitudes in the Andean cloud zone should perhaps be described as horticultural rather than agricultural. The terraces were not just revetments of the hillside but were specially constructed stone-lined troughs into which fertile soil was transported from the valley bottoms (Fig. 11.28).

The construction of terraces in the Andes along with a tradition of irrigation and terrace farming long predates the Inca civilization, with evidence of terrace farming beginning probably as early as 2400 BC. In the Colca valley in southern Peru evidence has emerged of terrace farming which began probably as early as 2400 BC (Denevan, 2001). Over the subsequent millennia

Fig. 11.29 Produce from a mountain farm in the Andes. A farmer near Sicuani (Peru) with a collection of maize and various tubers harvested from his farm. Note the variation in the maize and tubers that come from his one farm. The unconscious selection of maize, a C4 plant with an enhanced carbon dioxide harvesting system and high water use efficiency, was a fortuitous event for Andean terrace farming (see text).

Fig. 11.29 Produce from a mountain farm in the Andes. A farmer near Sicuani (Peru) with a collection of maize and various tubers harvested from his farm. Note the variation in the maize and tubers that come from his one farm. The unconscious selection of maize, a C4 plant with an enhanced carbon dioxide harvesting system and high water use efficiency, was a fortuitous event for Andean terrace farming (see text).

terrace construction took various forms depending on the terrain. Small narrow terraces predominate on steep mountainsides but on the lower slopes where the gradient is reduced broad gently sloping terraces like small fields were still constructed with irrigation canals to maximize production. In the Andes precipitation is a limiting factor and the careful construction of irrigation canals over the centuries made it possible to grow crops further up the mountainsides than would have otherwise been possible.

Terrace cultivation reached its maximum with the Inca Empire (AD 1200-1535) extending along the Andes from the Equator to the Pacific coast of Chile with an extensive range of crops including maize (Zea mays), quinoa (Chenopodium quinoa), various species of potato (Solanum tuberosum, S. acaule, etc.), as well as other Andean tubers such as caldas (Ullucus tuberosus), anu (Tropaeolum tuberosum), oca (Oxalis tuberosa) and ullucu (Ullucus tuberosus - Basellaceae), an Andean plant with potato-like tubers. Images of Oxalis tuberosa and Ullucus tuberosus have been documented on ceramics from the early pre-conquest era in southern Peru (Vargas, 1981). One highland archaeological site, Tres Ventanas at 3925 m, has yielded material of Ullucus tuberosus reputed to be 10000 years old (Sperling &

King, 1990). The highest cultivated plot in the world is recorded from near Lake Titicaca - a field of barley growing at a height of 4700 m (15 420 feet), too high for the grain to ripen but the stalks furnished forage for llamas and alpacas (www.crystalinks.com).

The domestication of maize (Fig. 11.29) and therefore the unconscious selection of a C4 plant as a cereal crop was particularly appropriate for the Andean situation. Not only are C4 plants economical in their use of water, their carbon dioxide harvesting system is ideally suited for the fixation of carbon in the high-altitude rarefied atmospheric environments. How and why the South American civilizations were able to have made the fortuitous selection of a C4 plant as a cereal provider is an intriguing question. A possible answer may be found in the palaeo-botanical history of the region. It has been argued that the altitudinal vegetation distribution in the northern Andes during glacial times differed from the present-day conditions as a result of temperature and precipitation changes. It is possible that reduced atmospheric partial CO2 pressure would alter the competitive balance between C3 and C4 plants in favour of the latter (Boom et al., 2001). In this connection it is also of interest that in the high plateaux of Tibet there is a marked predominance of C4 plants

Fig. 11.30 Northern Iceland showing eroding hillsides filling a level plain with soil, creating a potential for agriculture that did not exist at the time of the original ninth century settlement (landmm). (Photograph Dr Bjarni Gudliefsson.)
Fig. 11.31 A marginal farm in early summer in the Geiranger Fiord, Norway.

with 95% of the C4 species being found at altitudes above 3000 m (Wang, 2003).

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