Overstory #11 - Understory: A Unique Niche for Valuable Crops

(Note: Last issue, we highlighted the practice of Sequential Planting, or planting short-term crops in tree plantings to realize a return while waiting for long-term yields. This time, we focus on permanent interplanting of trees and crops in a layered agricultural system.)

Traditionally, tropical farmers have always managed and exploited the shady environment under trees, called the understory. There are many valuable cash and subsistence crops that thrive in the shady climate under trees. When cultivated in combination with tree or forest crops, understory crops enable farmers and foresters to diversify and increase their yields while reducing labor and making more efficient use of land. The understory is a niche worth cultivating.

Plantings that take advantage of the understory range from simple systems consisting of one species in the overstory and one in the understory, to complex systems with many layers of trees, shrubs, and herbaceous plants stacked together as appropriate for their needs.

A few successful examples involving a simple overstory/understory mix:

• Macadamia nut trees with coffee understory (Hawaii)
• Native forest areas cultivated underneath for traditional medicinal or culturally valuable plants (in Hawaii, these can include maile for leis, kava, and a variety of herbaceous medicinals)
• Timber trees (such as Cordia alliodora, or Laurel) with coffee or cacao underneath (Central and South America)
• Teak plantations with patchouli (an essential oil) underneath (Indonesia)
• Sesbania, a nitrogen fixing tree (for firewood, mulch, or animal fodder) supporting and shading passion fruit vines (Africa)
• Coconut plantations with taro, kava, or cattle underneath (Polynesia and Melanesia)
• Heavy-shade mixed reforestation projects with cut flowers and foliage (such as anthuriums, heleconias, etc.) underneath (Central America)

The understory is a unique environment, involving more than just shade. The shade trees provide brings about a whole complex of environmental changes, affecting not just available light but also air temperature, humidity, soil temperature, soil moisture content, wind movement, and more. These factors impact plants, and the effect can be very beneficial to a wide array of crops.

The moister, shadier, cooler microclimate in the understory can have the following effects:

• Reduces evapotranspiration (evaporation of water through the leaves and branches of the plant), conserving moisture in the plants and reducing water use and susceptibility to drought (provided the overstory trees are not overly competitive for water)
• Buffers crops from temperature extremes and fluctuations
• Naturally suppresses most invasive problem "weeds", which tend to prefer open conditions and full sun
• Supports a range of beneficial soil microlife that do not thrive in the open

The conditions in the understory will be determined by the kinds of trees that form the canopy above. Some trees create dappled sunlight or light shade; others create a thick canopy with dense shade beneath. Understory crops must be carefully selected so they are compatible with and make best use of the understory environment.

Examples of Understory Species

Here are a few examples of shade tolerant understory crops (some are highly shade-loving, some tolerate light shade only):

Essential oils: lemon grass, vetiver, patchouli

Spices: pepper vine, cinnamon, ginger, vanilla, cardamom, wild turmeric

Fruits: pineapple, annona species, and guava

Root crops and vegetables: taro, arrowroot, yams, long beans, and velvet bean

Herbs: oregano, basil, and chili pepper

Building/fiber materials: rattan, fan palms

Mushrooms: many culinary and medicinal fungi thrive in the understory

Other: coffee, tea, cacao, betel vine, kava

Some farmers discover that one of their current crops actually thrives in understory conditions, and rather than focus on exploiting their understory, they may look for trees to use as a canopy for their existing crop. Here in Kona, for example, several sustainable Kona coffee farmers are experimenting with interplanting timber or nitrogen fixing trees to provide a light canopy for their coffee trees.

The understory is a unique microclimate that enables farmers and foresters to diversify, increase their yields, reduce labor, and make more efficient use of land. As with any new venture, we recommend you research thoroughly, experiment carefully, and start small as you begin to explore the possibilities for your understory environment.

Do you know of a successful shade tolerant understory crop system not mentioned here? We invite you to write with your experiences!

References

International Institute of Rural Reconstruction. Agroforestry Technology Information Kit, 1990. IIRR, Room 1270, 475 Riverside Dr., New York, NY 10115. One of the most practical references in tropical agroforestry.

P. Ramachandran Nair, An Introduction to Agroforestry. 1993. Kluwer Academic Publisher. This comprehensive textbook bridges the gap between theoretical and practical knowledge in agroforestry.

W.C. Clark, R.R. Thaman (Editor), Agro-Forestry in the Pacific Islands: Systems for Sustainability. 1994. Unipub. Very thorough treatment of agroforestry practices in the Pacific. Includes list and descriptions of many agroforestry species.

Integrating Understory Crops with Tree Crops introduces planning considerations for planting crops with forestry, orchard, or other tree-based systems. Examples of understory intercropping systems in the tropics are included, as well as a species list of over 75 trees, shrubs, and vines used as understory crops.

About the Authors

Kim M. Wilkinson is the Education Director for Permanent Agriculture Resources and editor of The Overstory. She has B.A. degrees in Anthropology and Ecology from Emory University.

Craig R. Elevitch is an agroforestry specialist with more than ten years of public and private sector experience in tropical agroforest and forest management. He has a M.S. degree in Electrical Engineering (Dynamical Systems) from Cornell University.

Related Editions to The Overstory

• The Overstory #72--Microenvironments (Part 1)
• The Overstory #71--Nontimber Forest Products (Temperate)
• The Overstory #56 Integrating Understory and Tree Crops
• The Overstory #55 Nontimber Forest Products Part II: NTFP Enterprises
• The Overstory #53 Nontimber Forest Products--An Introduction
• The Overstory #33--Mushrooms in Agroforestry