Coffee (Coffea sp.) is a small understory tree or shrub, and has traditionally been grown amongst forest trees, in the shade. Various studies indicate that arabica coffee has the highest yields under 35 to 65% shade. In addition, growing coffee under shade also discourages weed growth, may reduce pathogen infection, protect the crop from frost, and helps to increase numbers of pollinators which results in better fruit set. Coffee grown in the shade takes long to ripen and is often thought to taste better because the long ripening times contribute to complex flavors.
However, in order to produce faster, higher yields and prevent the spread of coffee leaf rust (Hemileia vastatrix), many coffee plantations began to grow coffee under sunnier conditions. The fewer shade trees that are in coffee plantations, the less biodiversity there is in those plantations.
This loss of biodiversity, especially in birds, has led conscientious consumers to look for “shade grown” coffee. However, coffee is grown under a continuum of conditions, from rustic or traditional, to full sun, and these “shades of shade” are not all equal when it comes to the health of ecosystems. Unfortunately, there is no official definition of “shade grown,” so coffee so labeled may be grown under what are technically shady conditions, but which are little better full sun.
Categorizing types and levels of shade
It is important to understand the various levels of growing coffee under shade. Here are the five most typical categories, from the most desirable, traditional growing method, to the least diverse, most modern and technified method.
- Rustic. Often used on small family farms. Coffee is grown in the existing forest with little alteration of native vegetation. Tree species are diverse, with an average of 25 species. Shade strata (layers of vegetation) three or more. Shade cover = 70-100%.
- Traditional polyculture. Coffee is grown under a combination of native forest trees and planted tree and plant species, including fruit and vegetables both for the farmer and for market, fuel wood, medicinal plants, etc. Common tree species under which coffee is frequently grown include Inga, Grevillea, Acacia, Erythrina, and Gliricidia. Shade cover = 60-90%.
- Commercial polyculture. More trees removed in order to increase the number of coffee plants, and shade is provided mostly by planted timber and fruit trees. Canopy trees are regularly pruned, and epiphytes are typically removed. More often ivolves use of fertilizers and pesticides due to the lack of vegetative cover which helps prevent loss of soil nutrients, etc. Typically only two vegetation layers, the canopy, and the coffee. Shade cover 30-60%.
- Shaded monoculture. Dense plantings of coffee under an overstory of only one or two tree species (usually Inga), which are heavily pruned. Epiphytes are removed. Shade cover = 10-30%.
- Full sun. Lacks a tree canopy, or has a few isolated trees. No shade cover.
And here is a diagram from a paper by Patricia Moguel and Victor Toledo  to help you visualize the categories:
As you can see, coffee grown in a shaded monoculture could technically be labeled “shade grown,” but it would probably not be what the consumer, concerned about biodiversity, is looking for.
Benefits of growing coffee in the shade
The post “The problems with sun coffee” outlines some of the negative environmental impacts of growing coffee in the sun. Here are some of the benefits of growing coffee in the shade:
- Shade coffee supports biodiversity, and farms can act as wildlife corridors between plots of natural habitat. Numerous studies have shown that the diversity of birds, orchids, bats, ants, amphibians, bees, beetles, spiders, mammals, and other taxa are higher in shaded coffee than in sun coffee.
- Shade coffee provides pollination services, increasing the fruit set of coffee itself, as well as other plants on the farm.
- Shade coffee farms have a higher diversity of predators that help control coffee pests (just a few examples of research here, here, and here).
- Shade coffee typically has fewer weeds. Weeds often require more sunlight and are also controlled by the natural mulch supplied by fallen leaves from the shade trees.
- Nitrogen-fixing trees on shade coffee farms enrich the soil, as do the fallen leaves from the shade trees.
- Soil erosion is reduced in shade coffee, also improving soil quality.
- Shade coffee farms have more stable microclimates and can buffer against temperature and humidity fluctuations caused by climate change.
- Coffee grown in shade can improve quality.
- A diversity of shade trees can provide other economic benefits to farmers.
The Smithsonian Migratory Bird Center has developed standards that are targeted specifically at shade management and preserving biodiversity; their certification is called “Bird-Friendly” (this is a trademarked term and should always carry the Smithsonian seal). More on their criteria here. The Rainforest Alliance has a certification program for coffee that has an array of environmental standards, although shade cultivation is not a requirement. Their optional criteria is compared to the Bird Friendly criteria here.
See also Rice, R. 2010. The ecological benefits of shade-grown coffee: the case for going Bird-Friendly. Smithsonian Migratory Bird Center. (PDF)
 Biodiversity Conservation in Traditional Coffee Systems of Mexico. 1999. Conservation Biology 13:11–21.