From National Geographic:
After two years, the plot of land given a boost from coffee showed a dramatic improvement. Eighty percent of the plot was covered by young tree canopy, some trees already 15 feet—including tropical species that can grow as tall as 60 feet—versus just 20 percent in the untreated plot. In the coffee-fueled plot, trees were also four times taller on average, soil samples were more nutrient-rich, and invasive grasses had been eliminated.
Read more here.