Josh Slobin. A terraced field in Nepal.
Let’s plan for a short trip back in time, shall we? Jump in your favorite time machine, check the gauges and spin the dial. Destination: the Mediterranean basin in the Stone Age, the initial prehistoric landscape that allegedly witnessed the birth of agriculture and sedentary lifestyle. This auspicious and opportune location for long-lasting settlements from hunter-gatherers, who would colonize the area sometime around 12,000 BCE,1 is a landscape of grasslands, savannah, small hills, and low mountain ranges covered with large coniferous forests. The Mediterranean basin is famously heterogeneous, a patchwork of different microclimates hosting a large biodiversity, which transited from subtropical conditions to the climate we know today.
Let’s hop a bit forward in time: now imagine yourself walking in ancient Mesopotamia, the place from which Israel, Palestine, and Syria will rise up 40 centuries later. It’s a rough and rugged terrain, large plains giving way to rising hills and steeper mountains as you walk away from the ocean. Loam covers the soil everywhere, but if you were to dig you would quickly hit hard limestone within a meter. It’s a hot summer, although heavy rainfalls would come and last throughout the winter. Fields of ripening barley and lentils cover hillsides and riverbanks,1 cleared by the human hand of any forest, tree, or even scrubby bushes. Artificial irrigation ditches spread from the riverbed to the nearby fields. Agriculture flourishes, and the domestication of animals is in full swing.
Matt Spinner. Donkeys graze on terraces in Nepal.
In traditional sci-fi fashion, the passage of time now accelerates: around us harvests come and go, villages and cities are created, expanded, and deserted. Paths, then roads link communities together and witness increasing traffic as well as full-scale migrations. Time slows down: we are around 2000 BCE. The limestone bedrock is now clearly visible on the higher ground, the fertile soil dragged downslope by the rain and gravity with no native vegetation left to hold it back. Towards the rivers and the sea, swamps appeared from the accumulation of sediments, rendering the land inhospitable due to mosquito-borne diseases. The bare soil is scorched by the heat, having lost most of its ability to retain rainwater. The fields are not shining as much in the sunlight any longer, the yields decreasing with the exhaustion of the humus regeneration due to the cereal cropping technique (all mature crops are harvested and taken away for consumption, leaving none behind to replenish the soil).
Further up in the lower mountain ranges, it’s even worse: the declivity of the landscape sped up the rundown of fertile soil. Nonetheless, the ingenuity of humankind is at work: these uplands are now covered with rocky, winding terraces. These terraces, most often simply made from piled rocks, are uneven, narrow, and irregularly shaped, following the relief of the mountain. Each terrace holds a different crop variety, still allowing enough sustenance for the local population to thrive. Grazing goats bred for milk and meat are everywhere, eating any wild plant trying to conquer territory lost to human deforestation.
Back to the time machine for a final stop before heading home. Turning the dial forward 20 centuries, we find that the same land looks barely hospitable. Crops are scarcely to be seen. Armies came and went; Assyrians, Babylonians, and Romans conquered, destroyed, and enslaved. Populations were killed or displaced, the terraces not maintained, finally crumbling down the slopes along with all the fertile soil that was once retained. Each destroyed terrace makes the land even more inhospitable for crop husbandry, precipitating landscape degradation. What we describe as the Fertile Crescent, the cradle of civilization, is now a mostly arid land where farmers struggle to survive.2
This kind of scenario is not limited to the Mediterranean basin, although it is by far the most studied location. Terracing was an important concept in many agricultural traditions around the world. Along with the Mediterranean Basin, significant historical examples were found in Asia, Africa, and South America. It is highly unlikely that they influenced each other; rather, they are an example of how different cultures can hit upon the same solutions to solve similar environmental problems, in this case providing a sustainable agriculture by restraining, or even reversing, land degradation and erosion. This remains the single most efficient method against water-based erosion. Combined with modern tools, terracing might provide us with methods that improve upon those of modern farming, although many parameters have to be considered carefully. There is indeed much at stake: studies are unanimous in reporting that terrace destruction is worse for landscape sustainability than not building these terraces in the first place.
Christopher Rose. A terraced valley in Taray, Cusco, Peru.
As previously stated, terraces are an obvious solution for agriculture in high declivity terrain. However, they also offer much more than just being soil and water retainers. A controlled height allows for greater soil depth than the natural environment could offer, providing additional moisture to crops and potentially allowing crop varieties that could not flourish on shallow soil layers. A well-conceived terrace could retain water when needed or drain it according to a particular crop’s requirements. Potentially this water drain rate could even be altered every year in case of a crop rotation policy. According to the topographical orientation and the declivity of the slope, terraces could be built to provide the required sunlight exposure and air drainage for specific crops.3 Some even theorize that crop yields could be improved by terracing agriculture compared to traditional plain farming, although not in the first 10 years.4 There are modern instances where proper planning and design made a tremendous difference between failed terracing that left the land even more sterile (like in some regions of Rwanda) and successful land development leading to increased life conditions for rural populations (as in the Central Province of Kenya).5
The first obvious criterion is the terrain. Geology influences the type of terrace,6 but the cultural environment is also a factor.7 Terrace types can vary a lot. For example, they can be stepped, cross-channelled, or braided; they can have a narrow or a broad base, be parallel or perpendicular, and present different gradients and different outlets. A successful terracing project in a specific country is unlikely to be applicable on a different continent, in a different country, or even in a different region of the same country. Therefore, a local investigation has to be performed every time to predict the most successful terracing infrastructure, which is a painstakingly long process. Moreover, the local climate complicates things even further: in Iraq, without irrigation from natural springs, terracing for now is only economically viable in high precipitation areas with a seasonal rainfall of over 600 mm, where the gain would outweigh the high cost of construction and maintenance.8 In lower precipitation zones, terracing would only be worthwhile in higher declivity areas.
The second criterion is the required labour: besides the heavy machinery required for the initial drainage ditches and wall construction, conventional mechanized devices for plains farming obviously do not apply here—the shape and altitude of terraces are natural hurdles for such exploitation. However, the current development of precision farming might help to overcome these issues. Precision farming employs modern technology such as planes, GPS, and robotized devices to minimize the use of fertilizer and herbicide. Although such technology has mostly been applied to strip-cropping plains farming, it would surely be beneficial for terraces as well. Nonetheless, building the terraces themselves is not sufficient: additional agricultural practices must be standardized to maximize their use. Among them, the conservation of a permanent soil cover, the choice of adapted crops and their method of cultivation (e.g., rotation, strip cropping, etc.) as well as adequate contour ploughing and sowing are the most critical.4 Therefore, since terracing requires substantial additional efforts to cultivate compared to traditional plains farming,5 it is best suited to heavily populated rural areas.
Beyond geological and technical concerns, investing in terracing requires social, political, and financial stability. By far the most studied terraces are located on different Greek islands, where archeologists have studied their link to population changes.9 Nonetheless, we still do not understand thoroughly the ancient social context that led to the extensive building of these terraces. This point might deserve particular consideration to further ensure the local population in an area suitable for modern terrace farming fit a successful predictive model.9 Some terraces were in use up until the 20th century, suggesting the appearance and spread of terraces corresponds to increasing rural populations and more intensive farming. Their decline was largely due to massive urban migration, reducing the workforce and traditional knowledge of terrace building and maintenance.10
Bethan Phillips. Rice terraces in Yuanyang, Yunnan, China.
This is important to keep in mind for future development of terracing agriculture in developing countries. The African population in particular is still expected to grow exponentially before stabilizing to 2.5 billion in 2050.11 A massive social exodus towards urban centers could have a disastrous effect on decades of investment in terraces in rural lands that could be deserted. In France, Italy, and Spain such abandonment of traditional farmlands led to the quick reconquering by native vegetation, transforming the landscape into scrubland.10 Such transformation could have irreversible consequence on the agricultural potential of the land. For terracing, the lack of manpower means the slow erosion of the terrace by sheet wash, creating gullies that will carry the topsoil to valleys downstream.
Developing countries are also more likely to suffer from political instability. Terraces are infrastructure of strategic importance and likely worth fighting for. But once they have been taken down, whether through sabotage or the systematic destruction of a conquered territory, it has caused irreversible damage to the landscape, preventing any resettlement in a more peaceful future. Rwanda is a modern example of a civil war triggering serious setbacks in agricultural production when the genocide of 1994 prompted a sizeable part of the rural population to flee to neighbouring countries as refugees. The relative post-war stability, however, allowed for the reconstruction of terraces supported by governmental policies and NGOs.
Besides conflicts, the initial hefty investment into terracing a region in need would require a continuous injection of funds over several years and constant supervision. Due to the high cost of construction and maintenance, small landholders might only see benefits in the long run.12 State funding can be unreliable—the fast turnover of governments or the sudden appearance of politically more pressing matters might divert investments initially planned for such infrastructure development, especially if the benefits are not visible immediately. However, it is also unlikely that a local government would give free rein to an international organization to dictate their agricultural practices. Therefore, the origin of financial resources for such projects must be planned carefully.
In short, terracing agriculture is the most widespread traditional technique to enable farming in topographically difficult regions. Even now, terracing projects are envisaged in countries suffering severe drawbacks in their agricultural industry, such as erosion in Ethiopia and Iraq.8,13 Because terracing has huge potential both to slow down land degradation and improve the life conditions of local populations, it should be encouraged. However, since failed terraces create severe and sometimes irreversible problems for the landscape, terracing requires careful long-term planning in which political and social stability plays a vital role.
- Zeder, M. Domestication and early agriculture in the Mediterranean Basin: Origins, diffusion, and impact. PNAS 105(33), 11597–11604 (2008).
- Hillel, D. Out of the Earth: Civilization and the life of the soil (University of California Press, Berkely CA, 1992).
- Field, CA. Reconnaissance of Southern Andean Agricultural Terracing. National Academies (1966).
- Dorren, L & Rey, F. A review of the effect of terracing on erosion. Soil Conservation and Protection for Europe (SCAPE) [online] (2005). http://www.ecorisq.org/docs/Dorren_Rey.pdf.
- Johnson, DL & Lewis, LA. Land Degradation: Creation and Destruction (Rowman and Littlefield, Lanham MD, 2007).
- Grove, AT & Rackham, O. The Nature of Mediterranean Europe: An Ecological History (Yale University Press, London, 2001).
- Frederick, C & Krahtopoulou, A. Deconstructing agricultural terraces: examining the influence of construction method on stratigraphy, dating and archaeological visibility in Landscape and Landuse in Postglacial Greece (Sheffield Academic Press, Sheffield UK, 2000).
- Hussein, M et al. Designing terraces for the rainfed farming region in Iraq using the RUSLE and hydraulic principles. International Soil and Conservation Research 4(1), 39-44 (2016).
- Bevan, A et al. The long-term ecology of agricultural terrace enclosed fields from Antikythera, Greece. Human Ecology 41(2), 252-272 (2013).
- Petanidou, T et al. Socioeconomic dimensions of changes in the agricultural landscape of the Mediterranean Basin: a case study of the abandonment of cultivation terraces on Nisyros Island, Greece. Environmental Management 41(2), 250–266 (2008).
- United Nations, Department of Economic and Social Affairs, Population Division. World population prospects: the 2015 revision, key findings and advance tables. Working Paper No. ESA/P/WP.241 [online] (2015). https://esa.un.org/unpd/wpp/publications/files/key_findings_wpp_2015.pdf.
- Angima, SD et al. Soil erosion prediction using RUSLE for central Kenyan highland conditions. Agriculture, Ecosystems & Environment 97, 295–308 (2003).
- Hurni et al. Ethiopia case study: soil degradation and sustainable land management in the rainfed agricultural areas of Ethiopia: an assessment of the economic implications. The Economics of Land Degradation (ELD) [online] (2015). http://eld-initiative.org/fileadmin/pdf/ELD-ethiopia_i_06_72dpi-D.pdf.