Not quite. Humans found coffee growing in the forests of Ethiopia and Sudan. These plants were happy enough with the low light levels of the forest understory. They didn’t produce much coffee, but they produced enough that people found it worthwhile to farm the coffee deliberately. For the vast majority of coffee farming history, most coffee was always grown under the shade of trees because farmers struggled to keep plants healthy when they grew them in full sun. With the advent of synthetic fertilizers and then the Green Revolution, farmers discovered they could grow healthy coffee in the full sun. It was easier to grow and the trees produced much more coffee than they did in the shade.
How does this work?
Coffee, just like any plant, needs light, just as it needs water, nutrients, and carbon dioxide. Light often serves other purposes in plants in addition to being an ingredient for life. For many plants, light also serves as a signal to the plant. The light quality, quantity, and intensity can all convey information to a plant. This information can lead to a variety of changes in the plant.
Flower production is one factor that seems to be directly affected by light. Coffee plants exposed to lower light levels produce fewer flowers than plants exposed to higher light levels. With more flowers comes more coffee fruit and more coffee seeds. Thus, growing coffee in the shade produces less marketable product than growing the same plant in full sun.
When the plant produces more fruit than it otherwise would because of excess light, it requires more water, nutrients, and carbon dioxide. If nutrients aren’t available in sufficient quantities, the whole plant suffers because it can’t sustain the nutrient demand of the fruits. Short-term symptoms of nutrient deprivation include chlorotic (yellow) leaves followed by premature fruit ripening, then leaf and fruit drop. When this happens, not only is the current harvest affected, but the next harvest is as well. The only way to recover is to stump or heavily prune the trees and forego any harvest the following year.
So, in the shade of trees, coffee produces a small amount of fruit that can be sustained by the available nutrients. The only way to successfully grow coffee in full sun is to supplement the soil with sufficient nutrients (more water is needed, too, but the increase is smaller). When synthetic fertilizers became available, farmers realized they could grow coffee healthily, easily, and profitably in full sun. While full-sun coffee can also be grown successfully in an organic coffee production system, it is difficult and expensive. Thus, most farmers who grow organically have shade trees to help mitigate the plant’s nutrient needs.
Shade trees completely change the biological makeup of a coffee farm in all kinds of ways.
In summary, full sun coffee produces more coffee than shade coffee but it requires more inputs to make it successful. Actually, it isn’t that simplistic! Having or not having shade trees completely changes the agricultural and biological system of a coffee farm in all kinds of ways. Shade trees interact with the soil by adding nutrients via the decomposition of leaf litter, holding it in place (thereby preventing erosion), producing root exudates, and possibly bringing water from deeper regions to higher regions via hydraulic lift. Farms with a larger diversity of shade tree species tend to harbor a great deal of biodiversity, from ants to birds, whereas full sun farms tend to have relatively little biodiversity. Shaded systems encourage some pests and diseases while suppressing others.
Also, shaded systems tend to have fewer weeds (since weeds tend to be sun-loving).
Finally, shade trees can provide additional resources to farmers, like firewood or food.
There is also the question of whether shade (or light) has an influence on the flavor of the coffee. There is a romantic notion that because shaded coffee ripens slower and it can be part of a harmonious, complex, biodiverse system that it will taste better than coffee grown in full sun. The available data is noisy, meaning, some research shows a bit of a difference in taste while other research shows no difference in taste. Thus, one can interpret the data both ways. Taken all together, this scientist (who has done research on this very topic), concludes that the amount of light in which a coffee grows has no influence on its taste.
So, does coffee need sunscreen in the form of big trees? No, it can do just fine without it, so long as the farmer is able to supply it with the resources it needs. There are, however, many reasons why a farmer might choose to cultivate their coffee under shade trees.
Optimizing potential yield, though, is not one of them.
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