Restoration of Disturbed Lands: The Hole-in-the-Donut Restoration in the Everglades

The Hole-in-the-Donut (HID) wetland restoration project was established on former agricultural land inside Everglades National Park, where rock plowing and fertilization had altered the hydrology, structure, depth, aeration, and nutrient content of soils. Following the cessation of farming, highly disturbed HID soils were invaded by dense, nearly monospecific stands of Brazilian pepper (Schinus terebinthifolius Raddi). Initial efforts to restore Brazilian pepper-dominated areas failed, and only complete removal of the substrate down to the surface of bedrock was successful. Complete soil removal resulted in the restoration of a plant community dominated by native wetland plants. Following restoration, initially very shallow soils gradually deepened as marl accreted as due to the activities of periphyton. By 15 years postrestoration, an average of 3.7 cm of soil had developed. Initially low nitrogen concentrations increased following restoration, whereas phosphorus was converted to organic forms and diluted by the accumulation of marl. The result of these changes was a gradual switch from nitrogen limitation to phosphorus limitation, eventually mirroring the situation in adjacent undisturbed wetland sites. Complete substrate removal, as used in the HID, could be used to restore other areas of the Everglades degraded by nutrient enrichment.