Signs of Summer 9: More on Coffee

Photo by J. Scortzman, Flickr

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Coffee is, to me, one of the glorious aspects of life and living. The small trees and bushy shrubs of the genus Coffea yield “cherries” (red to purple, pulpy fruits) that contain the caffeine and flavor-rich seeds (the coffee “beans”) that can be roasted and ground up and then brewed into the wonderful, black beverage that so many of us love.

There are 124 species of Coffea and most grow wild in sub-Saharan Africa. Only two of these species are extensively cultivated to produce commercially traded coffee. Coffea arabica (“Arabian coffee”) makes up 60 to 70% of the coffee grown and sold around the world, and Coffea robusta makes up the remaining 30 to 40%. A study by botanists at the Kew Garden (“Royal Botanical Gardens”) in Great Britain, published earlier this year in both Science Advances and Global Climate Change Biology, determined that 60% of the wild Coffea species are at risk of extinction due to climate change and habitat destruction. The potential loss of this diverse and as yet poorly studied gene pool could leave cultivated coffee without the genes and proteins that it needs to survive in our climate changed world!

Coffea arabica was the first type of coffee to be domesticated. By the early Sixteenth Century it was widely consumed throughout the Middle East. It is native to the southern highlands of Ethiopia and arose, apparently, as a naturally occurring hybrid of two other Coffea species (C. robusta and C. eugeniodes). Most Coffea species have diploid chromosome arrangements, but C. arabica is tetraploid and contains the entire genomes of both C. robusta and C. eugeniodes.

Coffea arabica.Photo by H. Zell. Wikimedia Commons

In its natural habitat, C. arabica grows as an understory plant beneath tall shade trees. It is capable of self-pollination and relies primarily on wind dispersal of pollen (although wild bees greatly increase its overall pollination efficiency both in wild and domesticated systems). The traditional method of cultivation of C. arabica, which is practiced in more than 70 countries around the world, replicates this controlled, shady, growing environment.  In modern parlance this type of coffee growing system generates “shade grown” coffee beans. Coffee trees in shade grown coffee plantations can produce coffee beans for 30 years or more!

In the 1970’s, though, in an attempt to increase the productivity of coffee trees, sun tolerant varieties of Coffea were developed. Coffee could then be grown in vast, open, monocultural plantations that produced what is now called “sun grown” coffee beans. Sun grown coffee systems do have higher yields per tree, but its trees are only productive for about 15 years.

Sun grown coffee plantation in Kaua’i Hawaii. Photo by Lukas. Wikimedia Commons

Sun grown coffee was beset with a myriad of other problems, too. Increased levels of fertilizers, pesticides and herbicides were needed to fuel the increased productivity of the coffee trees and to fight intrusions of insect pests and weeds. Also, removal of the shading, over-story trees destroyed important habitats for a large number of native birds, mammals and reptiles (many of which were quite active in insect control!). A study published last year counted 204 species of birds living in the shade grown coffee plantations in the Western Ghats of India.

Removal of the protective tree cover also exposed soils to the often violent rain storms of the tropics and led to accelerated rates of soil erosion. Also, the quality of the coffee suffered. The accelerated coffee bean maturation rate in the sun grown trees generated beans with lower levels of important flavoring chemicals and higher levels of increasingly bitter acids. It was a lose/lose/lose/lose proposition! In Central America alone, over 2.5 million acres have been deforested to make room for sun grown coffee plantations.

Coffea robusta is particularly well adapted to sun grown coffee systems. Its flavor profiles are not as high in quality as those of C. arabica, but its higher caffeine content makes it a desirable crop. Many sun grown coffee plantations are dominated by C. robusta trees. Interestingly, C. robusta trees are not self-pollinating. They require the spread of pollen from one tree to the next and are much more dependent on insect pollen transfers than C. arabica. The monocultural nature of the sun grown coffee plantations, though, and their inherent dearth of nectar producing wild plants coupled with the extensive use of pesticides in the management of the system greatly reduced the abundance of potentially beneficial pollinating wild insects.

Shade grown coffee in Guatemala. Photo by J. Blake. Wikimedia Commons

Coffee trees of all types need stable environments to grow and thrive. This has been one of the ongoing arguments in favor of planting coffee trees in shade coffee systems. The micro-environments of the shade plantations fluctuate much less than they do in sun grown coffee systems. These more controlled environments may even serve as buffers against some of the predicted temperature and moisture consequences of climate change. The need for consistent growing conditions is also one of the explanations for the superiority of high altitude grown coffee over most low altitude grown coffee. Cooler, less fluctuating temperatures and lower atmospheric oxygen levels slow down the coffee tree’s rates of synthesis and maturation and enable the high altitude grown beans to develop their full flavor profiles and potentials.

Back in 2017 I wrote about some very disturbing studies concerning the sustainability of coffee cultivation. A report by the Climate Institute of Australia explored the impact of climate change models on the global distribution of coffee trees. They found that projected rises in global temperatures would reduce coffee producing land areas by 50% by 2050. Impact of climate change (which includes not only rising average temperatures but also changes in weather patterns and cycles of drought and excessive rainfall) were especially severe at low latitudes and low altitudes. The worldwide, tropical “bean belt” will need to move out of the afflicted tropical zones and up mountainsides in order to find suitable sites to grow coffee. It is estimated that there are 120 million people in these zones whose economic livelihoods depend on coffee.

The recent awareness of the multiple benefits of shade coffee have included not only an economic side (lower production costs), an ecological side (reduced pollution and soil erosion and establishment of complex habitats for birds and other animals), and also an aesthetic side (shade grown coffee tastes better!). Climate change, though,  may be too much even for these coffee ecosystems unless new genetic traits from the wild Coffea species can be found to extend coffee trees’ growth tolerance ranges into the “new normal” of our climate changed world.