Oak Flat Restoration on Phosphate-Mine Spoils

Phosphate mining in Beaufort County, North Carolina, impacts a rare plant community type, oak flats (nonriverine wet hardwood forests NRWHF]). Reclamation of land after mining utilizes three by‐products of mining and manufacturing: clay tailings containing dolomite, low‐pH phosphogypsum, and bucket‐wheel spoil from the surface 10 m. The open mine is backfilled with a blend of phosphogypsum and clay tailings, which may be left as the surface or capped with bucket‐wheel spoil. The objective of this study was to determine the feasibility of using these by‐products as substrates for restoring NRWHF. A field study measured survival of 11 tree and four shrub species planted in replicated plots of blend or bucket‐wheel spoil. Survival at the end of the second growing season was 59% on the blend and 52% on the bucket‐wheel spoil. A greenhouse experiment compared growth of four species of NRWHF oaks on bucket‐wheel spoil, blend, local topsoil (sterilized and unsterilized), and a commercial potting mix. Germination rates of acorns of all four species planted in topsoil were almost double those in bucket‐wheel spoil and 1.5 times greater than those in the blend. Height and stem volume of trees were significantly greater when grown in topsoil than in bucket‐wheel spoil and blend. There was no difference in tree growth on bucket‐wheel spoil and blend. In field and greenhouse soil tests, the blend had cadmium levels over 100 times that of local topsoil and the bucket‐wheel spoil had levels 40 times greater. Leaf chemical analysis in the field and greenhouse found higher cadmium levels in plants grown on the blend than on the bucket‐wheel spoil. These results indicate that the use of topsoil from the advancing mine front may lead to successful restoration of NRWHF.