Author: Paul O’Neil
It is common knowledge that agriculture alters traditional landscapes. The degree of this alteration greatly depends on the plant biodiversity in that agroecosystem. Plant biodiversity provides us many ecosystem services, such as; food security, ecosystem stability, positive effects on biodiversity of animals, aesthetics, and insurance against environmental change. These services not only provide us with a better well-being, but also provide us with life support systems. These services, however, are in threat due to conventional agricultural techniques that limit both genetic and species composition biodiversity. Oversimplification of plant diversity can have devastating effects on the health of that ecosystem, which in turn, has effects on our own health and security.
Agroecosystems that are multifunctional and diverse provide an array of ecosystem services in addition to just edible and biomass production, such as erosion control, carbon sequestration, nutrient cycling, wildlife support, and sources of spiritual and cultural enjoyment. These services interact with each other on many levels, allowing specific ecosystem functioning for that area. Many factors, such as fertility, disturbance, habitat size, climate, the presence or absence of trophic groups, and the functional composition of species can determine the relationship between biodiversity and ecosystem functioning (Ceroni, Lui, & Costnaza, 2007).
Genetic diversity is extremely important for human food security. Since life first appeared on the earth, the number of species has generally increased due to a process of continuous diversification, allowing a vast capacity for adaptation, while providing balance and stability within the biosphere. This stability is due to the coexistence of plants, each with different characteristics: some are resistant to specific diseases, some are tolerant to cold and others are to heat, some can grow in the shade while others cannot, etc. These traits allow ecosystems to become resistant to environmental changes along with being able to further adapt.
Due to the growing human population, the need for adequate food production has become a priority. The Industrial Revolution aimed to address this problem through intensification of monoculture systems. This led to a dramatic decrease in plant biodiversity; there are only 150 species that are now cultivated, with 12 kinds of plant species feeding the majority of the human population. This process of genetic erosion has dangerously shrunk the genetic pool that is available for natural selection, and for selection by farmers and plant breeders. It has also increased the vulnerability of agricultural crops to sudden changes in climate, and to the appearance of new pests and diseases (Esquinas-Alcázar, José, 2005).
There have been extensive studies, however, that show that diverse agroecosystems can produce a yield that is equal to or higher than that of monocultures, and does so without harming the environment. A case study of hay fields in Britain, for example, show how the restoration of species richness in areas previously impoverished in species biodiversity had a positive effect on hay production. The experiment included both species rich and species poor sites that were applied randomly. After two years, it was found that the species rich plots produced a 60% increase in production yield. This suggests that farmers can maximize high quality food production by maximizing biodiversity. A higher level of species richness can provide more opportunities for genetically superior traits, allowing species to evolve. (Ceroni, Lui, & Costnaza, 2007).
An example of agroecology and multifunctional land use can be shown through acase study of the Intervale Center. The Intervale is a diverse agricultural landscape located on a 280 ha floodplain located on rich alluvial soils where the Winooski River meets Lake Champlain. This area has evolved into a multifunctional site of agroecosystems that include land use in cultivated fields (27%), forest (19%), fallow fields (16%), and vegetative buffers (16%). The total treed habitat is 64.5 ha, encompassing 34.6% of the site. Greenhouses, built infrastructure, and the native plant nursery make up less than 1% of the land use. Ecological functions of this area are supported through agricultural management practices, such as organic crop production. Farmers are also required to plant cover crops on at least one third of their annual fields to allow regeneration. They are also required to rotate crops to increase soil fertility and reduce diseases in the fields. Non-crop landscapes are also applied to reduce erosion, conserve biodiversity, support native species, and provide habitat for wildlife. Other landscape features such as hedgerows, riparian areas, and forested areas are integrated throughout the site. Plants in windbreaks and hedgerows also encourage natural enemy populations of herbivore pests, making crops less susceptible to insect infestation, greatly reducing the need for inorganic inputs such as pesticides and fertilizers.
The Intervale Center also provides a composting area, which provides organic and nutrient rich fertilizers for the farm and surrounding areas. Because of the location of this land, however, there are negative effects of composting close to the Winooski River, such as waste runoff of phosphorous. However, the increased use of organic multifunctional agriculture is a healthy alternative to conventional agricultural practices, which would have many more negative effects on the land and waterways (Lovell, …Morris, 2010).
The case study of the Intervale Center can show how the structure of an agroecosystem affects the functions that it provides. The mixed land use and increased biodiversity of that area has allowed a greater amount of ecosystem functioning, providing us with valuable ecosystem services. For example, the structure of plants in windbreaks and hedgerows provides the function of supporting natural enemies for pests. This, in turn, translates into additional value placed on the structure and function. This allows farmers to manage pest control without the use of pesticides and other inputs while, at the same time, supporting the overall health of that ecosystem. Structural biodiversity of plants also provides functional support for pollinators, reducing the reliance of a single species pollinator. Also, cover crops and crop rotation are structures of the agroecosystem that provide a function of fertile soils. This also adds value by reducing the need for external fertilizer inputs.
Biodiversity structure in agroecosystems is also important for ecosystem resilience functions. In conventional agriculture, resilience is achieved through external inputs of chemical fertilizers, pesticides, and fossil fuels, which have high costs. In contrast, less intensive means of agriculture and high biodiversity along with farm management practices like that of the Intervale ensures this resilience without the need for external inputs; thus reducing the costs and raising the value. In order to be resilient to natural and market fluctuations, an agroecosystem should be able to withstand disturbance, be able to reorganize after disturbance, and have the ability to learn and adapt during periods of change. Diversity of wild pollinators are also needed for resilient systems in a time of declining pollinators. Southwick and Southwick (1992) calculated for each of the 62 US crops the extent to which wild pollinators could replace honeybee functions if they were to decline to the degree as predicted by their model. In the absence of wild pollinators, alfalfa production yield losses were estimated at about 70%, which is equal to U.S. $315 million a year. Revealing this cost can show the potential value of the function of wild pollinators.
Agricultural landscape diversity can also enhance bird and mammal species richness. For example, seed-eating birds seemed to have higher populations in pastoral areas that had arable land patches rather than pure grassland landscapes. An increase in wildlife has positive effects on overall ecosystem health. It is difficult to valuate biodiversity functions such as wildlife support systems, mainly because they affect us indirectly by increasing the resilience of that ecosystem. Valuation of this function can be assessed through the expenditures associated with the enjoyment of a biologically richer environment. For example, citizens of the Netherlands who had taken a survey were willing to pay an equivalent of $10.80 and $30.35 to fund management that would enhance wildlife habitat in the Dutch meadow region (Ceroni, Lui, & Costnaza, 2007).
Lovell, S. T., DeSantis, S., Nathan, C., Breton Olson, M., Méndez, V. E., Kominami, H. C., Erickson, D. L., Morris, K. S., & Morris, W. B. (2010). Integrating Agroecology and Landscape Multifunctionality in Vermont: An Evolving Framework to Evaluate the Design of Agroecosystems. Agricultural Systems, article in press, corrected proof . Retrieved April
8, 2010, from the ScienceDirect database.
Ecological and Economic Roles of Biodiversity in Agroecosystems. Marta Ceroni, Shuang Liu, and Robert Costanza. In Managing Biodiversity in Agricultural Systems. Jarvis, Padoch, and Coper Eds. 2007. Columbia University Press.
Protecting crop genetic diversity for food security: political, ethical and technical challenges . José Esquinas-Alcázar. Nature, December 2005, vol. 6