Coffee waste can become environmental medicine that regrows forests

LONDON — Tropical forests are a key ingredient in the recipe for maintaining life on Earth. They provide drinkable water, impact local rainfall distribution, and help to maintain Earth’s temperate climate by eliminating CO₂ from the atmosphere. However, people harvest this land each year, eliminating trees and vegetation by which millions of species thrive. Now, scientists have discovered that there may be an interesting way of saving these forests — coffee waste.

Coffee pulp
The researchers used 30 truckloads of coffee pulp to kickstart forest regeneration. (Credit: Rebecca Cole)

In the last five years alone, people have cut down more than 70 million acres each year. The rate at which this is occurring is significantly faster than the rate at which these forests can regrow. Dr. Rebecca Cole, a researcher from the University of Hawaii, along with a group of scientists from ETH Zurich, believe the solution to help tropical forests rebuild themselves in a shorter period of time is by using coffee pulp.

Coffee pulp, a waste product of coffee production, is rich in organic compounds. Humans have used it for agricultural purposes before, but only in small amounts. With coffee factories pumping out tons of the byproduct each year, the waste has proven difficult to dispose of. This prompted Cole and her team to investigate its beneficial properties on a wider scale.

For the study, the team spread nearly 700,000 pounds of coffee pulp over a third of an acre in Costa Rica cleared of everything except for grass. The pulp covered the surface by about 1.5 feet. As a control, they left an area roughly the same size untreated.

Coffee just the right boost for richer forests

The team collected and tested samples of soil just before adding the pulp and once more after completing the two-year investigation. Additionally, the team made a log of the species living in the area, as well as the thickness and height of nearby trees and shrubs. Researchers estimated the amount of forest floor covered by the canopy, as well as the amount of canopy present in areas surrounding the research plot. Drones kept track of this information before, during, and after the investigation.

Year 3 Coffee pulp
The recovering forest 3 years after coffee pulp was applied to the area. (Credit: Rebecca Cole)

“The results were dramatic.” says Dr. Cole, the study’s lead author, in a media release. “The area treated with a thick layer of coffee pulp turned into a small forest in only two years while the control plot remained dominated by non-native pasture grasses.”

In the 24-month period, the portion with pulp grew back a canopy that covered nearly 80 percent of the entire plot. The control section was only able to regrow a small section of a canopy that covered about 20 percent.

Additionally, the pulp seemed to eradicate obtrusive species of grass, enabling the growth of indigenous trees, which towered over the shorter trees in the control region. According to the soil tests, the coffee pulp added nutrients such as nitrogen, phosphorus, and carbon to the soil, all of which are essential for sustaining healthy plants.

“This case study suggests that agricultural by-products can be used to speed up forest recovery on degraded tropical lands. In situations where processing these by-products incurs a cost to agricultural industries, using them for restoration to meet global reforestation objectives can represent a ‘win-win’ scenario,” Dr. Cole adds.

Giving back to former coffee fields

The land researchers picked for this study sits in the county of Coto Brus. Ironically, it was once cleared and used as a plantation to grow coffee beans. The clearing of the land eventually decreased the amount of natural vegetation by one-quarter. Given that people produce roughly 10 million tons of coffee pulp yearly, this seems to be the best way to get rid of the byproduct and restore forests quicker.

“This study was done at only one large site so more testing is needed to see if this strategy works across a broader range of conditions. The measurements we share are only from the first two years. Longer-term monitoring would show how the coffee pulp affected soil and vegetation over time. Additional testing can also assess whether there are any undesirable effects from the coffee pulp application,” Cole continues.

Some limits to the study include the leveled area that was easier for trucks to reach, as well as possible containment of nutrient run off. This would deplete some of the essential nutrients from the treated area and leak into nearby water sources. The team would like to continue the research using larger areas of land and areas with different terrain. Additionally, they would like to test other biodegradable, nutrient-rich products as fertilizers.

“We would like to scale up the study by testing this method across a variety of degraded sites in the landscape. Also, this concept could be tested with other types of agricultural non-market products like orange husks. We hope our study is a jumping-off point for other researchers and industries to take a look at how they might make their production more efficient by creating links to the global restoration movement,” Cole concludes.

The findings are published in the journal Ecological Solutions and Evidence.