In 1998, an unusual idea in northwest Costa Rica offered one answer. Trucks dumped an estimated 12,000 metric tons of orange pulp and skins on a devastated cattle pasture. Most of us throw away the orange peels without a second thought. A juice factory can end up with mountains of them, and somebody has to decide where they go. It sounds like a dumping story. But a peer-reviewed study published in the journal Restoration Ecology by a Princeton University team led by Timothy Treuer shows how the waste helped that land regrow as forest.
Treuer’s team compared the treated area to an adjacent untreated plot that year. In a follow-up commentary in Tropical Conservation Science , the authors suspected the peels did two things, though they could not confirm it. Within a couple of months, the waste had killed the grass, probably by smothering it. It then broke down into a nutrient-rich layer that may have helped tree seedlings take hold. That’s why the researchers couldn’t be sure what drove the recovery. The authors noted that more research was needed to figure out the right amount of waste. They also called for careful pilot tests including runoff into waterways and greenhouse gas emissions. Most of the citrus growers who spoke to the team farm in Mediterranean climates, where results could be different.
After 16 years, the treated plot had three times as many species of woody plants. It also had 176% more woody biomass above ground, that is, wood in the trunks and branches. The canopy photos showed denser cover, and the soil samples taken two and 16 years after the peels were dropped showed higher levels of nutrients. This was just one 3-hectare site, and the project was never repeated. The peels were from several hundred hectares of orchards but were used on only 3 hectares.
