Orange is the new green: Accelerating tropical forest regeneration in Costa Rica using citrus waste

Background/Question/Methods

Ecological restoration has enormous demonstrated potential for slowing or reversing biodiversity loss particularly given trends in urbanization and globalization leading to abandonment of marginal agricultural land. However, the common perception that active restoration projects are prohibitively expensive at scales useful for protection of regional biodiversity has forestalled their widespread implementation, and passive regeneration can be slow or entirely arrested with the legacy of various land-uses.  One under-explored low-cost or no-cost solution involves using agricultural wastes to fertilize dystrophic soils on abandoned lands. To explore this possibility, we investigated a site in Área de Conservación Guanacaste (ACG), Costa Rica, where a landmark deal between ACG and Del Oro S.A., a local orange juice company, led to the carefully supervised application of 1,000 dump truck-loads of processed orange peels in January 1998 on a 3 hectare abandoned cattle pasture within ACG.  In 2000, soil samples were taken at the site. More expansive surveys were conducted in 2014 including collection of additional soil samples, establishment of vegetation transects, hemispherical photography, and invertebrate pitfall trapping in both the treatment site and an adjacent control site.

Results/Conclusions

The 2000 soil analyses confirmed what was obvious from visual inspection: orange peels greatly increased the fertility of the soil. The 2014 survey confirmed lasting changes in nutrient profiles. Vegetation surveys and hemispherical photography revealed a 2-4 fold increase in aboveground biomass, a 3-fold increase in plant biodiversity for trees larger than 5cm in DBH, and a 3-fold increase in canopy closure, as compared to an abutting control plot. Invertebrate pitfall traps demonstrated an approximately 5-fold increase in number of invertebrates captured relative to the control, but without significant differences in the family richness. These results emphatically confirm observational findings from an experimental plot of 100 dump truck-loads of peels deposited at a separate site in 1996, namely that this process is a marvelous and pragmatic way to rapidly begin the forest recovery process if there are seed sources nearby, dispersal processes in motion, no humans to be offended, and a diverse array of insects from which a biodegredation community will be attracted.