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Coffee waste can stimulate the restoration of tropical forests

Year 3 Plot for coffee pulp

The regenerating forest 3 years after the application of cellulose from coffee on the area Credit: Rebecca Cole.

A new study finds that coffee pulp, a waste product from coffee production, can be used to accelerate the recovery of tropical forests in post-agricultural land. The findings are published in the Journal of the British Environmental Society Environmental solutions and evidence.

In the study, researchers from ETH-Zurich and the University of Hawaii sprayed 30 dump trucks with pulp on 35 × 40 m of degraded land in Costa Rica and identified a similar area without coffee pulp as a control.

“The results were dramatic,” said Dr. Rebecca Cole, lead author of the study. “The area treated with a thick layer of cellulose from coffee became a small forest in just two years, while the control site remained dominated by foreign pasture grasses.”

In just two years, the coffee pulp-treated area had 80% roof coverage, compared to 20% in the control area. The canopy in the coffee pulp area was also four times higher than in the control area.

The addition of a half-meter-thick layer of coffee pulp eliminated the invasive pasture grasses that dominated the soil. These grasses are often a barrier to forest succession, and their removal allows local pioneer tree species, which arrived as seeds by wind and animal dispersal, to relocate the area quickly.

Delivery of coffee pulp

The researchers used 30 trucks of pulp to start forest regeneration. Credit: Rebecca Cole.

The researchers also found that after two years, nutrients, including carbon, nitrogen and phosphorus, were significantly elevated in the treated area of ​​coffee pulp compared to controls. This is a promising discovery, as former tropical agricultural lands are often severely degraded and poor soil quality can delay forest acceptance for decades.

Dr Cole said: “This case suggests that agricultural by-products can be used to accelerate reforestation in degraded tropical lands. In situations where the processing of these by-products leads to costs for the agricultural industries, their use for recovery to achieve the global reforestation targets may be a “profitable” scenario.

As a widely available waste product with a high nutrient content, coffee pulp can be a cost-effective reforestation strategy. Such strategies will be important if we are to achieve ambitious global targets for the restoration of large areas of forest, such as those agreed in the 2015 Paris Agreements.

The study was conducted in Coto Bruce County in southern Costa Rica on a former coffee farm that is being restored in the forest for conservation. In the 1950s, the region underwent rapid deforestation and the conversion of land to coffee farming and forest-covered pastures, reduced to 25% by 2014.

Edge Between Coffee Pulp and Control Plot

The difference between the coffee pulp and the control plot after 1 year. Credit: Rebecca Cole

In 2018, researchers outlined two areas of approximately 35 × 40 m, spreading coffee pulp in a layer half a meter thick on one area and leaving the other for control.

The researchers analyzed soil nutrient samples just before applying the coffee pulp and again two years later. They also recorded the species present, the size of the tree trunks, the percentage of forest land cover and used drones to record the canopy roof.

Dr. Cole warns that, as a two-year case study, further research is needed to test the use of coffee pulp to help reforestation. “This study was done on only one large site, so more tests are needed to see if this strategy works in a wider range of conditions. The measurements we share are only from the first two years. Longer-term monitoring would show how coffee grounds affect soil and vegetation over time. Additional tests can also assess whether there are any side effects from the application of coffee pulp. “

A limitation on the use of cellulose from coffee or other agricultural by-products is that its use is limited to relatively flat and accessible areas where the material can be delivered and the risk of added nutrients being washed away in nearby catchments.

For further research on the use of coffee pulp, Dr Cole said: “We would like to expand the research by testing this method in various degraded areas of the landscape. This concept can also be tested with other types of agricultural non-market products such as orange peel.

“We hope that our study is a leap for other researchers and industries to see how they can make their production more efficient by creating links to the global recovery movement.”

Reference: “Coffee pulp accelerates the early succession of tropical forests in old fields” by Rebecca J. Cole and Rakan A. Zahawi, March 28, 2021, Environmental solutions and evidence.
DOI: 10.1002 / 2688-8319.12054

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