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Agroforestry and the Maintenance of Biodiversity

Peter Bichier

articlehighlights

Agroforestry is a land-use method that allows trees to grow in crop and livestock areas. Studies have shown that it

  • is one way to conserve biodiversity
  • attracts species beneficial to farming, such as pollinators
  • improves farms by, for example, reducing soil erosion
  • is economically beneficial to farmers

April 2006

Biodiversity is the total variety of living entities on Earth.
bichierphoto.jpg

International Center for Research in Agroforestry (ICRAF): Experimental plot growing trees with crops, Kenya. Photo by CGIAR.

As living entities on this planet, we are at the mercy of the Earth’s living conditions just as any other species. Simply put, we are just another passenger on the ship called Earth. The difference, however, is that we are affecting life in a way that no other species has and altering our planet at a much faster rate. In particular, human activity and specifically habitat destruction have dramatically increased rates of biodiversity loss.

Biodiversity is:

Biodiversity supports human well-being.
  • the total variety of living entities on this planet including all living organisms, as well as their surrounding habitats, or ecosystems, and the genetic material of which they are made1
  • extremely important to maintain the proper functioning of ecosystems and society; it is the diversity of life that makes this planet extraordinary
  • a provider many services and uses, as well as being a source of aesthetic joy: oil, coal, cement, and limestone are all part of the past biodiversity on which our economies depend and the majority of our medicines and agricultural crops come from the environment
  • also important for providing ecosystem services such as pollination and pest control.

Even though humankind only uses a few species of crop plants, ensuring that agriculture is carried out in a manner compatible with biodiversity is crucial.

Agricultural systems and biodiversity

Less than 7 percent of global land areas are protected.

Traditional approaches to biodiversity conservation focus on protecting natural habitats in parks and reserves while ignoring the possibilities found within certain agricultural habitats.2 Preservation is necessary to maintain native habitats and those species reliant on pristine habitats, but very little land area is currently protected.

  • The total amount of land in protected areas worldwide in 2004 was estimated at only 6.1 percent of the total land area.3
  • In contrast, approximately 75 percent of arable lands are now cultivated in some sort of agriculture4 and in large part are contributing to the destruction of biodiversity.
Agriculture can play a role in protecting biodiversity.

Increasingly, however, conservation biologists are incorporating some agricultural systems into their management plans as important refuges for biodiversity. The general concept underlying incorporation of agricultural areas is that if a certain percentage of land is dedicated to environmentally friendly and sound agriculture, and another percentage of pristine habitat is protected, then preserving the two land uses in combination can contribute to the capacity of the planet to keep us afloat. In order to protect biodiversity, the thinking goes, we need to incorporate agricultural lands managed to protect the environment and therefore our own survival. In contrast, continuing with inappropriate land use will deplete our resources and destroy the remaining biodiversity at ever increased rates.

That we need to incorporate agriculture to save biodiversity may come as a surprise to those who envision agriculture as a wasteland. Yet some agricultural areas with trees may protect as much biodiversity as neighboring forests and provide other benefits necessary for proper ecosystem functioning.5,6 Agricultural systems that differ in number of crop plants and vegetation structure can be located along a gradient of intensification from areas where crops are grown under natural forest canopies (agroforests) to intensively managed areas with only one crop plant (monocultures).7

Monoculture was heavily promoted in the 1970s under the guise of the green revolution. Techniques included planting large expanses with a single crop to increase efficiency and yield and adding high inputs of fertilizers, pesticides, and herbicides. The green revolution promised to increase crop yields and feed a growing population. Many still argue that using such intensive techniques in smaller land areas will allow protection of more habitats for wildlife conservation.8

Intensive farming is not sustainable in the long run.
  • Although such techniques may allow short-term yield increases, the costs of intensive and extensive agriculture continues to place a great toll on biodiversity and native habitats, and these negative effects are not limited to the particular agricultural habitats in which they are practiced.4,9
  • Pest resistance to pesticides also became a problem causing widespread overuse of chemicals and subsequent pollution.
  • Furthermore, intensive production systems have resulted in overproduction of many crops and as a consequence a price decline, making it harder for farmers to continue making a living from agriculture.10

Intensive agriculture also intensifies the problem of forest fragmentation. Even in large forest fragments, there are high levels of species extinction, especially when the fragments are isolated.11 Thus a strategy focusing on intensive agriculture with pesticide applications and intensive monocultures will further isolate those fragments and will prevent movement of individuals between fragments.5 In contrast, when forest fragments are embedded within high quality matrix that promotes interfragment movement, there is a high probability that forest populations can be maintained as metapopulations.12,13

Agroforestry systems allow trees to grow with crops.

Agroforestry systems, in contrast to intensive monocultures, may provide such high quality habitats important for biodiversity conservation. Agroforestry systems are broadly defined as agricultural systems where trees are grown together with annual crops and/or animals, resulting in enhanced complementary relations between components and increased multiple use.14 Agroforests often fall at the least intensive end of the agricultural spectrum; agroforestry systems such as coffee, cacao, or jungle rubber, where crops are grown under a diverse and dense canopy of trees, protect biodiversity and are a far cry from the images of agriculture as the enemy. Particularly among tropical agroforestry types, shaded coffee and cacao have received the most attention and study. Coffee and cacao were traditionally cultivated under a diverse, dense shade canopy, but recent production is characterized by increased management intensity: reducing shade tree density and diversity, shade tree pruning, and use of agrochemicals.15

Agroforests and maintenance of biodiversity

Farmers’ choices influence biodiversity directly and indirectly.

In general, scientists refer to two types of biodiversity:

  • Planned biodiversity encompasses the variety of plants and animals chosen and placed in the system by the farmer. Examples generally include crop plants and livestock.
  • Associated biodiversity comprises all other species attracted to or found within the system apart from the farmer’s plans. Examples include wildlife such as birds and mammals, soil organisms, and weeds.7
Numerous studies highlight the impact of agroforestry.

Agricultural intensification, moving along the gradient from agroforests grown with a diverse and dense shade canopy to those agroforests with only a few types of trees to monocultures with only one crop species or cattle pastures, by definition includes a reduction in the planned biodiversity. Agricultural intensification also results in a loss of associated biodiversity. The following key studies in a range of agroforest types and other agricultural systems document losses in associated biodiversity (relative to nearby forest fragments) with increasing agricultural intensification:

  • In several agricultural and forest habitat types sampled in Chiapas, Mexico, bird diversity was highest in forest, but it was closely followed by woodlots and shaded coffee agroforests, each supporting approximately 105 species of birds. Other habitats sampled, such as cattle pastures, multigrain fields, arboreal pastures, and pine savannas, had many fewer species.16
Farms in Mexico, Panama, and Costa Rica support bird and insect diversity.
  • In Panama, of 11 habitat types sampled for bird species, wooded habitats (including forests, shaded coffee agroforests, and residential areas) supported many more bird species than introduced pine plantations or sugar cane and at least twice as many species as active cattle pastures.17

  • Insects were sampled from trees in three coffee agroforest types in Costa Rica: traditional (with the highest diversity and density of trees), moderate, and unshaded. Ant diversity across the three types decreased from 22 species per tree in the traditional agroforest to 5 species in the moderate type to 0 species found in the unshaded plantation. Similarly, beetle diversity decreased from 118 in the traditional plantation to 48 in the moderate type to 0 in the unshaded type.18

  • In coffee agroforests in Chiapas, Mexico, samples of fruit-feeding butterflies revealed that diversity was similar in forest and coffee agroforests with high density and diversity of trees, but only a half to a third as many species were found in coffee agroforests with few trees.19

Other species, such as bats, were drawn to agroforests.

Although only a few studies are presented here, many more show similar patterns for other groups of animals and plants, including small mammals, bats, bees, and epiphytes, in a range of geographic locations.20 The pattern is clear: diverse agroforestry systems provide important habitat for biodiversity, especially when they are compared with other agricultural systems. Although less is known about the long-term maintenance of biodiversity within these systems, or the ability of species to reproduce in agroforests, much work has been carried out recently and is underway to determine what factors promote and maintain biodiversity in agroforests. Factors that are known to be important for the maintenance of biodiversity generally include high plant diversity, including any species necessary for reproduction or food, and a variety of microclimates and microhabitats to support diverse life forms and species.21,22

Overall benefits of agroforestry systems

Agroforests benefit biodiversity, which in turn can benefit the agroforest functioning and humans.

Agroforests

Farmers benefited economically, and farms were more arable.
  • provide habitat for biodiversity to live and breed:
    -predator species that protect crop plants from pest outbreaks.23
    -pollinator species important for ensuring harvests of important crops.24-26

  • act as buffers to protected areas, in other words, protecting them from the direct effects of more intensive agriculture and human settlements.

  • create a high quality matrix that increases the movement of animals from one protected area to another and increasing the overall connectivity of natural habitats.12,13

  • reduce soil erosion, increase carbon sequestration, increase water uptake and storage.27

  • provide economic benefits to farmers through the large diversity of crops produced.28

Agroforestry and sustainability

Land use must be both ecologically and economically sustainable.

The problem of conserving biodiversity goes hand in hand with larger issues of social and economic development: Land use must be both ecologically and economically sustainable. If practiced in a sustainable manner, agroforests can contribute toward these goals. Sustainable use is defined generally as use of components of biological diversity in a way and at a rate that does not lead to the long-term decline of biological diversity, thereby maintaining its potential to meet the needs and aspirations of present and future generations.1 Ecologically, agricultural systems need to be oriented in such a manner that they can last longer than just a few years. Agroforests provide one significant way in which this can be done, but it is important they be managed organically. Organic agriculture—eliminating chemical use and promoting soil enriching practices—works hand in hand with agroforests in promoting sustainable agricultural systems.

Agroforests can provide incomes from many alternative sources.

Economically speaking, agroforests can provide incomes from many alternative sources as well as provide materials and foods used by the farmers. In contrast to sun crops, frequently grown solely for export and with often volatile markets, diverse agroforests produce many crops, buffering the ups and downs of international markets. Diverse systems with high levels of biodiversity also have better ecosystem services, increasing local functions of pest control23 and pollination,24-26 often with high economic returns. In sum, agroforestry systems are not only ecologically sustainable ways to grow crops but also provide income and resources to farmers and protect biodiversity.

The future of agroforestry

To protect biodiversity and other benefits that biodiversity provides, agroforestry systems should continue and expand, especially in buffer zones near protected areas. There are two basic ways to encourage agroforestry systems:

  • Provide incentives to the farmers that already have agroforestry systems.
  • Restore vegetation in monoculture systems with perennials and tree crops.
Farmers need economic incentives to implement agroforestry.

Although growing crops under existing forest canopies would easily create very diverse agroforests, it is problematic if farmers turn to existing forests and especially forest reserves to do so.29 However, it is important to provide farmers who already have agroforestry systems with economic incentives to prevent them from turning agroforests into intensive monocultural systems.30 Creating agroforestry systems by restoring degraded agricultural habitats is one way in which to avoid the problem of forest conversion while still maintaining and promoting recovery of biodiversity. In such a restoration process, sun coffee, for example, slowly transformed to shade coffee. Furthermore, areas with sun grown crops like vegetables can be planted with sun tolerant trees, such as cinnamon, allspice, and fruit trees, which eventually grow into shade tolerant hardwoods. This process leads to recovery of forested areas with diverse canopies from which people still can retrieve economic benefits.

Agroforests offer a win-win situation for both biodiversity and humans.

Conclusion

Agroforests provide important habitats for biodiversity, ecologically sustainable buffer zones for protected areas, a high quality matrix that promotes movement between forest fragments, and ecosystem services such as pest control, pollination, and erosion control. Furthermore, agroforests produce important sources of income for local people. It is possible to see agriculture as a diverse system and treat it as an extension of natural habitats that can be guided to grow our needs.

An ActionBioscience.org original article

Agroforestry and the Maintenance of Biodiversity

Read a Book

Read the book reviewed in BioScience (May 2005), “Agrobiodiversity: Learning from Farmers across the World,” FREE to read on Google books.
http://books.google.com/books?id=JAJOO7FVvmUC&printsec=frontcover&source=gbs_v2_summary_r&cad=0#v=onepage&q=&f=false

Convention on Biological Diversity

A wealth of information is available about biodiversity, its uses, and efforts to preserve the world’s species.
http://www.biodiv.org

Smithsonian Migratory Bird Center

This research center has been a leader in investigating the effects of agricultural transformation on biodiversity. Their website contains information about relevant research and also about promoting Bird Friendly® Coffee in efforts to preserve habitat important for migratory birds.
http://nationalzoo.si.edu/scbi/migratorybirds/

National Agroforestry Center

Basic information, articles, and other resources from the USDA’s Forest Service and Natural Resources Conservation Service.
http://www.unl.edu/nac/

Center for Tropical Research in Ecology, Agriculture, and Development (CenTREAD) at University of California-Santa Cruz

People at this research center are involved in investigating the role of agroforests and other agricultural systems in sustainable food production and biodiversity conservation.
http://centread.ucsc.edu

World Agroforestry Centre

This research institution has links to publications, research, and further information on agroforestry worldwide.
http://www.worldagroforestry.org

Introduction to Permaculture: Concepts and Resources

Textbook-style information about designing ecological human habitats and food production systems.
http://attra.ncat.org/attra-pub/perma.html

National Campaign for Sustainable Agriculture

Engage in grass roots efforts that result in healthy, environmentally sound agricultural systems and rural communities that are profitable, humane, and just.
http://www.sustainableagriculture.net

Sustainable Agriculture Research and Education

This group “advance[s] farming systems that are profitable, environmentally sound, and good for communities through a nationwide research and education grants program.”
http://www.sare.org/About-SARE

For consumers and coffee farmers: Bird Friendly® Coffee

Find out where you can purchase the coffee with the bird-friendly seal. The coffee is guaranteed to be grown in areas that support migratory birds. Coffee growers can learn how to get their farms certified for the program.
http://nationalzoo.si.edu/scbi/migratorybirds/coffee/default.cfm

Agroforestry-related lesson plans

  1. The Convention on Biological Diversity: http://www.biodiv.org (accessed Oct. 8, 2005)
  2. United Nations Environment Programme World Conservation Monitoring Centre. 2004. World Database on Protected Areas. CD-ROM. Cambridge, UK. http://sea.unep-wcmc.org/wdbpa/download/wdpa2004/index.html (accessed Oct. 8, 2005)
  3. McNeely, J. A., and S. J. Scherr. 2003. Ecoagriculture: Strategies to feed the world and save wild biodiversity. Washington, DC: Island Press.
  4. Vandermeer, J., and I. Perfecto. 2005. The future of farming and conservation. Science 308: 1257-1258.
  5. Garcia-Barrios, L. 2003. Plant-plant interactions in tropical agriculture. Pages 11-58 in J. H. Vandermeer (ed.). Tropical Agroecosystems. Boca Raton, FL: CRC Press.
  6. Perfecto, I., and I. Armbrecht. 2003. Technological change and biodiversity in the coffee agroecosystem of northern Latin America (Chapter 6. Pages 159-194 in J. Vandermeer (ed). Tropical Agroecosystems. Boca Raton, FL: CRC Press.
  7. Swift, M. J., J. Vandermeer, P. S. Ramakrishnan, J. M. Anderson, C. K. Ong, and B. A. Hawkins. 1996. Biodiversity and agroecosystem function. Pages 261-298 in H. A. Mooney, J. Cushman, E. Medina, O. Sala, and E. Schulze (eds). Functional Roles of Biodiversity: A Global Perspective. New York: John Wiley and Sons.
  8. Green, R. E., S. J. Cornell, J. P. W. Scharlemann, and A. Balmford. 2005. Farming and the fate of wild nature. Science 307: 550-555.
  9. Dietsch, T. V., S. M. Philpott, R. A. Rice, R. Greenberg, and P. Bichier. 2004. Conservation policy in coffee landscapes. Science 303: 625-625.
  10. Gresser, C., and S. Tickell. 2002. Mugged: Poverty in your cup. Washington, DC: Oxfam International.
  11. Ferraz, G., G. J. Russell, P. C. Stouffer, R. O. Bierregaard, S. L. Pimm, and T. E. Lovejoy. 2003. Rates of species loss from Amazonian forest fragments. Proceedings of the National Academy of Sciences 100: 14069-14073.
  12. Vandermeer, J., and R. Carvajal. 2001. Metapopulation dynamics and the quality of the matrix. American Naturalist 159: 211-220.
  13. Steffan-Dewenter, I. 2002. Landscape context affects trap-nesting bees, wasps, and their natural enemies. Ecological Entomology 27: 631-637.
  14. Nair, P. K. R. 1982. Soil Productivity Aspects of Agroforestry. Nairobi, Kenya: ICRAF.
  15. Moguel, P., and V. M. Toledo. 1999. Biodiversity conservation in traditional coffee systems of Mexico. Conservation Biology 13: 11-21.
  16. Greenberg, R., P. Bichier, and J. Sterling. 1997. Bird populations in rustic and planted shade coffee plantations of eastern Chiapas, Mexico. Biotropica 29: 501-514.
  17. Petit, L. J., D. R. Petit, D. G. Christian, and H. D. W. Powell. 1999. Bird communities of natural and modified habitats in Panama. Ecography 22: 292-304.
  18. Perfecto, I., J. Vandermeer, P. Hanson, and V. Cartin. 1997. Arthropod biodiversity loss and the transformation of a tropical agroecosystem. Biodiversity and Conservation 6: 935.
  19. Mas, A.H., and T. V. Dietsch. 2004. Linking shade coffee certification to biodiversity conservation: Butterflies and birds in Chiapas, Mexico. Ecological Applications 14: 642-654.
  20. Donald, P. F. 2004. Biodiversity impacts of some agricultural commodity production systems. Conservation Biology 18: 17-37.
  21. Perfecto, I., and J. Vandermeer. 1996. Microclimatic changes and the indirect loss of ant diversity in a tropical agroecosystem. Oecologia 108: 577-582.
  22. Armbrecht, I., I. Perfecto, and J. Vandermeer. 2004. Enigmatic biodiversity correlations: Ant diversity responds to diverse resources. Science 304: 284-286.
  23. Perfecto, I., J. Vandermeer, G. Lopez, G. Ibarra Nuñez, R. Greenberg, P. Bichier, and S. Langridge. 2004. Greater predation of insect pests in diverse agroecosystem: The role of resident neotropical birds in shaded coffee farms. Ecology 85: 2677-2681.
  24. Klein, A. M., I. Steffan-Dewenter, and T. Tscharntke. 2003a. Bee pollination and fruit set of Coffea arabica and C. canephora (Rubiaceae). American Journal of Botany 90: 153-157.
  25. Klein, A. M., I. Steffan-Dewenter, and T. Tscharntke. 2003b. Fruit set of highland coffee increases with the diversity of pollinating bees. Proceedings of the Royal Society of London B 270: 955-961.
  26. Ricketts, T. H., G. C. Daily, P. R. Ehrlich, and C. D. Michener. 2004. Economic value of tropical forest to coffee production. Proceedings of the National Academy of Sciences 101: 12579-12582.
  27. Beer, J. R., R. Muscheler, D. Kass, and E. Somarriba. 1998. Shade management in coffee and cacao plantations. Agroforestry Systems 38: 139-164.
  28. Somarriba, E., C. Harvey, M. Samper, F. Anthony, J. González, C. Staver, and R. Rice. 2004. Biodiversity conservation in neotropical coffee (Coffea arabica) plantations. Pages 198-226 in G. Schroth, G. Da Fonseca, C. Harvey, C. Gascon, H. Lasconcelos, and A. Izac (eds). Agroforestry and Biodiversity Conservation in Tropical Landscapes. Washington, DC: Island Press.
  29. Rappole, J. H., D. I. King, and J. H. Vega Rivera. 2003. Coffee and conservation. Conservation Biology 17: 334-336.
  30. Philpott, S. M., and T. Dietsch. 2003. Coffee and conservation: A global context and the value of farmer involvement. Conservation Biology 17: 1844-1846.

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