Agroecology

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Agroecological approaches maximise the number, diversity and quality of interrelationships among the organisms, species and populations at a site. Agrodiversity is usually a key dimension: in addition to using diverse species and varieties agroecological design locates these in both space and time in ways that maximise their beneficial interactions, including creation of microclimates. This strengthens ecological processes such as nutrient cycling, enhancement of soil life and biological suppression of pests and diseases.[1]

Agroecology is neither restricted nor original to permaculture, being characteristic of many traditional and indigenous farmings systems worldwide, some with histories extending centuries or even millenia.[2] Many of the common features of agroecological production worldwide reflect strategies farmers take to minimise exposure to risk of hunger due to crop failure in climates that are often marginal and/or unpredictable. This predisposes them for climate resilience in many different ways.[3]

Studies of recovery of farms in Nicaragua, Honduras and Guatemala after Hurricane Mitch in 1972 showed that compared to conventional farms, agroecological farms retained greater levels of topsoil, soil moisture and vegetation cover, and suffered lower levels of erosion and economic losses. The difference was higher the longer the land had been under agroecological production, and increased with increasing storm intensity.[4] In the 1992 droughts that severely impacted much of Southern Africa, female farmers in several districts of Zimbabwe mitigated the impact on food security through permaculture, water management, and use of agrodiversity, focusing on drought-tolerant crops.[5]

The Himalayan Permaculture Centre in Nepal supports farmer-led innovation, along with implementation of scientific research by establishments like Cornell University on sustainable rice intensification (SRI). Although focused on a single crop, SRI takes the agroecological approach of creating optimum systemic conditions for rice plants to flourish. It does this by giving careful attention to individual seedlings, promoting aerobic soil conditions for root growth and cultivating a conducive microbial ecology, and controlling weeds by mechanical methods that allow their incorporation into the soil.[6]

In the Food Forest, a 30-year-old permaculture site in Australia, sheep and geese graze between rows of trees, restricting growth of weeds. This eliminates any need for mechanical weeding or herbicide application, both of which are energy-intensive and polluting. It also allows retention of ground cover vegetation, which helps to reduce evaporation of water from the soil in this increasingly dry climate. The animals provide a range of additional products (meat, down, manure etc.), are more self-reliant in food, help clear the ground of fallen fruit, and can benefit from the shade and cooling effect of the trees. Integrated assemblages of species, each of which benefits the others, seek to mimic the resilience and self-regulation of natural ecological systems. They provide a system that is more productive overall, includes buffers and safeguards against changing conditions for each species, and at a systemic level is more resilient and adaptable to climate impacts than one dedicated to a narrower range of outputs. They also have unexpected emergent effects: the Food Forest initially provided a home for bettong, an endangered wild marsupial, purely for altruistic reasons. It later became apparent that they help with weed control by digging up and eating bulbs of the invasive exotic plant Oxalis, and with revegetation by burying seeds of native acacia trees, many of which later germinate.[7]

Best known in Europe, and to many people emblematic of temperate climate permaculture, [forest gardens] take the structure and ecological dynamics of a forest as a template for agroecological design.[8] Structurally, they include up to seven vertical layers, each made up of plants of similar size and habit. Dynamically, they mimic natural processes of succession by supporting the growth of different plants throughout the year. They provide seasonal microclimates for sun-loving plants in early spring, and for shade-tolerant plants at lower levels in summer once the trees are in full leaf. In addition to edible and other directly useful plants, some plants primarily fulfil ecological functions such as nitrogen fixation, attracting pollinators, and providing wildlife habitat, as well as human amenity value. Associations among cultivated plants and wildlife create emergent agroecological effects such as soil health, exchange of nutrients and pheromones among plants, and keeping pest and pathogen populations in check. An initial survey of newly-planted forest gardens in the UK reported that many had achieved success in overcoming adverse weather conditions, for example by planting windbreaks and creating warm microclimates. Almost all reported visible increases in biodiversity in many different taxa, including arthropods, reptiles, birds and annelids.[9]

References

  1. Altieri, M., 1987. Agroecology. Boulder: Westview Press.
  2. Altieri, M., 1983. Agroecology. Berkeley: Division of Biological Control, University of California, Berkeley.
  3. Altieri, M. A., 2004. Linking Ecologists and Traditional Farmers in the Search for Sustainable Agriculture. Front. Ecol. Environ. 2(1): 35-42.
  4. Holt-Giménez, E., 2002. Measuring farmers’ agroecological resistance after Hurricane Mitch in Nicaragua: a case study in participatory, sustainable land management impact monitoring. Agriculture, Ecosystems & Environment 93(1): 87-105.
  5. Altieri, M. A., & P. Koohafkan, 2008. Enduring farms: Climate change, smallholders and traditional farming communities. Third World Network (TWN). Pp. 15-16.
  6. http://www.independentsciencenews.org/un-sustainable-farming/how-millions-of-farmers-are-advancing-agriculture-for-themselves/
  7. http://www.foodforest.com.au/fact-sheets/animals/bettongs/
  8. Jacke, D. & E. Toensmeier, 2005. Edible Forest Gardens. White River Junction: Chelsea Green.
  9. Remiarz, T., 2014. Ten Year Forest Garden Trial. Third Year Report. Leeds: Permaculture Association UK. http://www.permaculture.org.uk/sites/default/files/page/document/year_3_report_trials_v4_14-11-18.pdf.