Did you know that in the past 50 years, agriculture has grown between 2.5 and 3 times? This continued increase is to support a growing population. However, the expansion of modern agriculture leads to biodiversity decline worldwide. Biodiversity loss has been associated with lower plant productivity - and even lower yields, which is not good! Wouldn't it be good if we could sustainably expand agriculture without facing biodiversity loss and yield decline? One method is creating agroecosystems, which we will cover in this article.
Agroecosystems: Definition
Agroecosystems are natural communities that have been modified by humans for agricultural purposes.
Agroecosystems refer to the relationships and interactions between abiotic and biotic factors (including humans) in a physical space - as well as the agricultural processes themselves.
Food security refers to reliable access to a sufficient quantity of affordable and nutritious food. Food security is dependent on a healthy and sustainable food system.
The food system encompasses all stages of the journey from fields to our plates:
Production → Processing → Distribution → Marketing → Acquisition → Consumption
Types of Agroecosystems
Agroecosystems have been used for thousands of years among indigenous societies - they recognised the important connection between agriculture and natural systems. Only in the 20th century did agroecology come about as a discipline in western science.
The types of agroecosystem vary depending on:
- Location
- Natural community
- Agricultural focus
Polyculture (Intercropping)
Polyculture differs greatly from modern, industrial monocultures. Instead of huge expanses of one plant, different complementary crops are interspersed, producing mutual benefits.
Many American Indigenous cultures cultivate the 'three sisters' - corn, beans and squash.
The three plants grow symbiotically and support each other - and provide a balanced diet from a single planting.
- Tall corn stalks support the growing bean stalks.
- Beans 'fix' nitrogen from the atmosphere, transferring it to the soil to provide nutrients for the other two plants.
- The large sprawling leaves of the squash create a mulch that shades the soil, keeping it warm and moist. The prickly leaves ward off pests such as slugs.
Polyculture strategies can save land area by up to 29% compared to monocultures - making them very useful in the journey to sustainable agricultural expansion.
Permaculture
Permaculture systems create synergies and imitate natural systems. These systems apply holistic techniques to support ecosystem function, integrating a range of functions (e.g. hydrology, livestock, waste management).
Paddy fields are artificially created wetlands for growing rice that support a range of animals and plants. Modern paddy fields often experience pollution and emit greenhouse gases. However, traditional paddy fields can be viewed as an example of a permaculture system.
- Traditional rice systems use sustainable practices that reduce water pollution and reduce emissions of greenhouse gases and nitrous oxide.
- Systems that incorporate fish aquaculture experience mutually beneficial effects.
- Plant leaves create shade, cooling the water for the resident fish.
- Fish act as biological pest control agents, feeding off insects that eat the growing rice. Fish also naturally fertilise the system - reducing the need for chemicals and their associated pollution.
Permaculture has been adopted as a design system in many other aspects of life. It's about working with, rather than against, nature. The permaculture philosophy focuses on earth care, people care, and fair shares.
Permaculture designs can be applied to urban areas, finance, technology, culture, education, and health and well-being.
Agroforestry
Agroforestry encompasses the growth of trees and crops, and managing animals for mutual benefit.
Silvopastoral Systems
Silvopastoral systems combine livestock with mixed plants such as trees, grasses and shrubs.
These systems are common in Latin America, and typically combine grazing pastures and trees - such as timber plantations or fruit trees. These pastures are incorporated among trees or using rows of trees to provide borders. Grazing is rotated between different pastures to allow time for recuperation.
Trees provide shade and shelter, providing favourable conditions for the livestock and improving their welfare, while animals provide manure that fertilises the land.
When compared to modern farming methods, silvopastoral systems show improved animal welfare, increased biodiversity, and increased production of meat and dairy. Furthermore, silvopastoral systems also support climate mitigation.
Sheep grazing in vineyards is an example of a silvopastoral system.
Agrisilvicultural Systems
Agrisilvicultural systems combine crops and trees.
Coffee is frequently grown in agrisilvicultural systems. Coffee is grown beneath fruit and legume trees, or those destined for timber. These systems promote a high level of biodiversity, aid with pollination, reduce the need for chemical fertilisers, and help sequester carbon. From an economic standpoint, shade-grown coffee helps farmers achieve greater profits.
Agrosilvopastoral Systems
These systems combine all three elements of crops, forests and pasture.
Silvopastoral systems combine forests and pasture, while agrosilvopastoral systems add crops to the mix.
The Spanish dehesa is a widespread example of an agrosilvopastoral system. Spanning 4 million hectares, it promotes both nature conservation and sustainable rural development. Its main features are the Mediterranean climate and low soil fertility.
Pigs wandering freely in a Spanish dehesa.
Components of Agroecosystems
Agroecosystems consist of two components: abiotic and biotic.
Abiotic Components
- Climate: temperature, light intensity, day length, CO2
- Resources: water availability, nutrient supply
- Landscape: topography, relief
- Soil: fertility, salinity, pH
Biotic Components
- Pests: parasites, herbivores
- Competition: between plants
- Symbiotic relationships: subterranean organisms, pollinators
- Farmers: includes their management of (a)biotic factors
Symbiotic relationships are ecological relationships where two species live in close contact. Typically, small prokaryotes form symbiotic relationships with much larger organisms - for example, mycorrhizal fungi and plants. The fungi's hyphae (branching filaments) increase the surface area of the plant's roots, helping plants absorb water and essential nutrients from the soil.
Characteristics of Agroecosystems
Agroecosystems are categorised by types of diversity.
Planned diversity focuses on the domesticated plants and animals (and beneficial organisms) that are deliberately added to the system.
Unplanned diversity focuses on other organisms in the system after conversion to agriculture (e.g. predators, weeds, microbes).
Interactions between Planned and Unplanned Diversity
Planned diversity can impact overall ecosystem functioning. Modern industrial agricultural systems have much lower diversity (including genetic diversity) than traditional systems. Reduced genetic diversity leaves plants and animals susceptible to pests and diseases, which have often adapted to exploit the most common varieties.
Low genetic diversity was the main driver of the infamous Irish Potato Famine of the 1840s. Almost all farmers grew the Irish Lumper potato variety, resulting in homogenised crops. When the crops were infected with the potato blight fungus, farmers had no backup varieties to grow. Ireland faced starvation, with a shocking 1 million citizens dying and another 1 million emigrating.
A potential mitigation strategy is genetically engineering agricultural products to have increased resistance to these diseases and pests.
Alternatively, promoting increased diversity can help reduce these problems and increase overall resistance. Furthermore, increasing planned diversity also increases unplanned diversity. This benefits agricultural production by delivering services such as pollination, pest control and soil health.
Biodiversity in Agroecosystems
Agroecosystems support a greater level of biodiversity compared to monocultures. This helps agroecosystems perform a range of services outside of food production - nutrient cycling, regulating climate and hydrology, detoxification, and many more.
Agroecosystem Biodiversity Components
- Productive Biota: another term for planned diversity. Productive biota plays a key role in determining the complexity and diversity of the agroecosystem.
- Resource Biota: organisms contributing to the agroecosystem's productivity through services such as pollination and decomposition.
- Destructive Biota: weeds, insects and pathogens. Farmers aim to limit their effects through management.
Restoring Biodiversity in Agricultural Landscapes
Restoring the functional biodiversity of agricultural landscapes is an important step toward expanding sustainable agriculture. This improves soil fertility and ecosystem productivity.
Functional biodiversity quantifies the components of biodiversity that influence how an ecosystem operates.
It has been proven that increasing the diversity of an agricultural system promotes increased yields, production and stability. A higher diversity also suppresses weed and pest species - a study found that 53% of pest species were less abundant in a more diverse system.
As monoculture yields continue to decline or decelerate, increasing diversity could become key for sustaining production and maintaining ecosystem services.
I hope that this has clarified agroecosystems for you. Remember that an agroecosystem is a natural community modified for agricultural processes and that it encompasses the interactions between species and the environment too.
Agroecosystems - Key takeaways
- Agroecosystems are natural communities modified by humans for agricultural processes. The term also refers to the relationships and interactions within the system.
- The types of agroecosystems include polyculture, permaculture and agroforestry.
- Agroecosystems include abiotic and biotic factors - the latter also includes the farmer and their activities to manage the system.
- Agroecosystems are characterised by planned and unplanned diversity. Increasing planned diversity promotes unplanned diversity, benefitting agricultural production.
- High biodiversity is a key feature of agroecosystems. This promotes high yields, production and stability as well as suppressing diseases and pests.
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