Slow-forming terraces

Slow-forming terraces made with festuca arundinacea and citisus monpesulanus, Ecuador. Photos from Fantappiè (2006).

Slow-forming terraces refers to a nature-based solution (NbS) that involves the construction of terraces or stepped structures using natural materials and vegetation. The cultivation of marginal land in the Andes and soil erosion problems lead to the development of the slow-forming terraces soil conservation method in the 1980s (Kraemer et al., 2019), though other similar methods have been used in parts of Africa, Asia, and Te Moananui Oceania. 

Unlike traditional terracing methods, which typically use concrete or stone, slow-forming terraces are built gradually over time through the accumulation of sediment, organic matter, and plant growth. These terraces are designed to slow down the flow of water, reduce erosion, and improve soil retention on slopes. By mimicking natural processes and promoting ecological restoration, slow-forming terraces contribute to sustainable land management and climate resilience. They are often implemented in areas prone to soil erosion, such as hillsides and riverbanks, to mitigate the impacts of runoff and flooding.

The terraces are formed by a redistribution of topsoil from the upper to the lower part. Barrier stripes, made of grasses and/or bushes and trees, keep the new soil in place, which then develops into a terrace. Some concerns was raised about how this process would affect soil fertility.  Kraemer et al. (2019) showed that over a 17 year time period where slow-forming terraces had been employed, slope gradients were decreased significantly, and soil quality was greatly enhanced.

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Name of NbS

Slow-forming terraces

Type of NbS

Created or constructed living ecosystems; Ecosystem restoration

Location

Slow-forming terraces could work in urban, periurban, or rural parts of Te Moananui Oceania that have steep slopes.

Restored lo‘i (taro ponds) at Limahuli Gardens, Hawai’i. Photo from Pacific Worlds.

Relationship to Indigenous knowledge

Although ‘slow-forming terraces’ is a concept from outside of Te Moananui Oceania, the practice of terraced and irrigated creekfield taro (colocasia esculenta) agriculture was common in some of the seasonally dry regions of many Pacific Islands. This system has been described as technically sophisticated, intensive, highly productive and ecologically sustainable; with links to social stability and enhanced biodiversity (King, 2016). Allen (1971) describes the decline of terracing systems to grow taro in Viti Levu Fiji, New Caledonia, Hawai’i, Tahiti, and on Rarotonga in the Cook Islands for various reasons including colonisation, and provides detail of terraces still in use at that time in Mangaia, Cook Islands. Campbell (2003) also examines terracing systems in the Cook Islands. Kuhlken & Crosby (1999) examine a late prehistoric irrigated terraced agrosystem at Nakauvadra, Viti Levu, Fiji. Koshiba et al. (2014) discuss how terracing is key to 2000 years of sustainable land and reef management in Palau.

Others illustrate similar systems in the Solomon Islands (Bayliss-Smith & Hviding, 2015) and Vanuatu. Terracing is still practised on the Fijian island of Kadavu (Kuhlken, 2002), and is being restored in many areas including in Fiji (King, 2016), and in Hawai’i. Smith (2014) notes:

‘The cultivation of taro ultimately takes place in a wet pondfield environment provided either by a naturally swampy site or through irrigation technology. Infrastructure often involves diversion dams, aqueducts and terracing using logs or stone-faced walls. Unlike terraces in other parts of the world which may be built to retard soil erosion or simply to provide level planting area, the irrigated taro terraces of the Pacific are designed to control the flow of water. This pondfield environment provides the ultimate medium for growth of taro. Water must never be allowed to stagnate, but must always flow slowly through the gardens . . [this] regulates the temperature of the garden. Cooling the taro stalks and helping to prevent corm rot. The rich saturated soil layer is constantly nourished by the nutrients delivered in the flowing water. In low lying ground, saturated soils necessitate the construction of raised beds. These landforms may be found throughout Oceania from New Guinea to East Polynesia [and in Micronesia] and range in design from simple to elaborate.’

The relationship between Indigenous knowledge and slow-forming terraces lies in the recognition and integration of traditional ecological practices and wisdom into modern soil conservation and management strategies. Indigenous communities often possess deep knowledge of local ecosystems, including sustainable land use practices and techniques for soil conservation and water management. Incorporating Indigenous knowledge into the design and implementation of slow-forming terraces can enhance their effectiveness and sustainability. Indigenous practices, such as agroforestry, contour farming, and the use of traditional building materials, may offer valuable insights into creating terraces that are better adapted to local environmental conditions and cultural contexts.

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Climate change benefits
  • Biomass cover loss
  • Changes in phenology (life cycle timing changes in plants and animals)
  • Changes in rainfall
  • Desertification
  • Drought
  • Freshwater flooding
  • Increased temperatures
  • Loss of food production
  • Reduced soil quality
  • Soil erosion
  • Urban heat island effect

Research indicates that the historical expansion of irrigated taro creekfield ethnoagriculture (Indigenous ways of farming), across the Pacific Islands was a response to evolving environmental and social conditions. With the onset of climate change driven by global warming, the region faces heightened environmental volatility (Kumar, 2020). Agriculture must adapt to these changes. Traditional methods, developed to withstand past challenges, may become increasingly relevant. Embracing approaches that integrate Indigenous knowledge with new technologies to enhance resilience could be useful (King, 2016).

The climate change adaptation benefits of slow-forming terraces include soil erosion control, water retention, flood mitigation, and carbon sequestration.

Slow-forming terraces help reduce soil erosion by slowing down the flow of water on slopes. This reduces the risk of soil loss due to heavy rainfall, preserving fertile topsoil and preventing sedimentation in water bodies. By trapping water and allowing it to infiltrate into the soil, slow-forming terraces promote groundwater recharge and increase soil moisture levels. This helps to sustain vegetation during dry periods and reduces the impacts of drought on agricultural productivity. Slow-forming terraces can help manage floodwaters by absorbing excess runoff and reducing peak flow rates downstream. This helps to prevent flash flooding and protect downstream communities and infrastructure from flood damage. Vegetation established on slow-forming terraces acts as a carbon sink. This helps to mitigate climate change by reducing greenhouse gas emissions and enhancing carbon storage in terrestrial ecosystems.

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Societal / socio-cultural benefits
  • Disaster risk reduction
  • Economic and social development
  • Food security and quality

The socio-cultural adaptation benefits of slow-forming terraces include fostering community cohesion and resilience through collaborative construction and maintenance efforts. Engaging local communities in terrace-building activities may promote traditional knowledge sharing and strengthen cultural identity. 

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Ecological and biodiversity benefits
  • Climate regulation
  • Disturbance prevention (erosion, storm damage, flooding etc.)
  • Fixation of solar energy
  • Food production (for humans)
  • Nutrient cycling
  • Pollination
  • Purification (of water, soil, air)
  • Soil building
  • Species maintenance

Slow-forming terraces can create diverse microhabitats for plant and animal species, promoting biodiversity in degraded landscapes. Vegetation cover on terraces provides habitat for wildlife and supports ecosystem functions such as pollination and soil stabilisation.

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Technical requirements

The technical requirements of slow-forming terraces encompass various aspects from initial assessment to ongoing maintenance. Site assessment involves evaluating topography, soil types, and hydrological conditions to identify suitable locations. Design considerations include optimising water retention, erosion control, and biodiversity enhancement while respecting local ecological and cultural contexts. Selecting appropriate materials, such as rocks, logs, and vegetation, is crucial for construction. Implementing techniques that minimise soil disturbance and ensure terrace stability during construction is essential. Establishing regular maintenance practices, including weed control and erosion repair, sustains terrace functionality and effectiveness over time.

Slow-forming terraces system of the Tunzun terraces in the Andes. Barrier stripes consist of fruit trees and grasses and corn is cultivated together with climbing beans and squash. Image by Kraemer et al. (2019).

Issues and Barriers

Potential barriers and issues for slow-forming terraces in Te Moananui Oceania include limited funding and resources, hindering their implementation and maintenance. Cultural considerations, including land tenure and community engagement, may impact project acceptance and collaboration. Additionally, technical challenges, such as site suitability and material availability, pose practical obstacles. Climate change impacts, such as increased rainfall variability and extreme weather events, may affect terrace effectiveness and resilience.

Opportunities

A key opportunity for using slow-forming terraces in Te Moananui Oceania might be the cultural revitalisation potential in areas with historical or contemporary terracing traditions. The opportunity to preserve Indigenous land management practices, while stabilising soil, increasing soil fertility and addressing food security issues exists. Slow-forming terraces support food security, biodiversity conservation, and ecosystem resilience, contributing to sustainable development in Pacific Island communities.

Financial case

The financial case for slow-forming terraces in Te Moananui Oceania lies perhaps in their cost efficiency, long-term savings, economic diversification, and ecotourism potential. Terraces may offer a cost-effective solution for soil conservation, resulting in reduced maintenance costs over time. Slow-forming terraces tend not to be labour or cost-intensive and don’t require expensive equipment or materials (Kraemer et al. 2019). Slow-forming terraces may provide both immediate and long-term economic benefits.

The communally owned and operated irrigated terrace system at Ravitaki, Kadavu, Fiji. Photo by Kuhlken (2002).
First planting of dalo (taro) in refurbished terraced vuci creekfield, Nakoro, Noikoro district,
Navosa, Viti Levu, Fiji, 2012. VNV-FOSLE project. Photo by King (2016).


References
  • Allen, B. (1971). Wet-field taro terraces on Mangaia, Cook Islands. The Journal of the Polynesian Society, 80(3), 371-378.
  • Bayliss-Smith, T. P., & Hviding, E. (2015). Landesque capital as an alternative to food storage in Melanesia: Irrigated taro terraces in New Georgia, Solomon Islands. Environmental Archaeology, 20(4), 425-436.
  • Campbell, M. (2003). Productivity, production and settlement in precontact Rarotonga, Cook Islands. Archaeology in Oceania, 38(1), 9-22.
  • Fantappiè M. (2006). Conservation and reclamation of volcanic deteriorated soils in Ecuatorian Ands. Available online: http://www.infoandina.org/sites/default/files/publication/files/ARTICOLO.pdf. Date accessed 5 May, 2024.
  • Kiddle, G. L., Pedersen Zari, M., Blaschke, P., Chanse, V., & Kiddle, R. (2021). An Oceania urban design agenda linking ecosystem services, nature-based solutions, traditional ecological knowledge and wellbeing. Sustainability, 13(22), 12660.
  • King, T. (2016). Irrigated ethnoagriculture, adaptation and development: a Pacific case study. The Journal of Pacific Studies, 184.
  • Koshiba, S., Besebes, M., Soaladaob, K., Ngiraingas, M., Isechal, A. L., Victor, S., & Golbuu, Y. (2014). 2000 years of sustainable use of watersheds and coral reefs in Pacific Islands: A review for Palau. Estuarine, coastal and shelf science, 144, 19-26.
  • Kraemer, N., Dercon, G., Cisneros, P., Lopez, F. A., & Wellstein, C. (2019). Adding another dimension: Temporal development of the spatial distribution of soil and crop properties in slow-forming terrace systems. Agriculture, ecosystems & environment, 283, 106543.
  • Kuhlken, R., & Crosby, A. (1999). Agricultural terracing at Nakauvadra, Viti Levu: A late prehistoric irrigated agrosystem in Fiji. Asian Perspectives, 62-89.
  • Kuhlken, R. (2002). Intensive agricultural landscapes of Oceania. Journal of Cultural Geography, 19(2), 161-195.
  • Kumar, L. (Ed.). (2020). Climate change and impacts in the Pacific. Cham, Switzerland: Springer.
  • Smith, A. (2014). Cultural landscapes in the Pacific Islands: the 2007 ICOMOS thematic study. Safeguarding Precious Resources for Island Communities World Heritage Paper Series, 38, 52-59.

Further resources:

Irrigated Taro (Colocasia esculenta) in the Indo-Pacific: Biological, Social and Historical Perspectives (2012). Spriggs, M., Addison, D., & Matthews, P. Osaka: National Museum of Ethnology.