Long-term vegetation recovery on reclaimed coal surface mines in the eastern USA

Published source details Holl K.D. (2002) Long-term vegetation recovery on reclaimed coal surface mines in the eastern USA. Journal of Applied Ecology, 39, 960-970.
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Summary

A study was initiated to determine whether vegetation communities on reclaimed coal surface mines in Virginia(eastern USA) resembled those of surrounding forest, and to evaluate how intensive reclamation practices used to address short-term erosion and water quality concerns affect long-term recovery.

Study sites: In 1992-93 and 1999, the vegetation on 15 quarter-hectare coal surface mines reclaimed between the years 1962-87, and five periodically logged hardwood forests (for use as comparative reference sites) in southwestern Virginia were surveyed.

The sites reclaimed in 1962-67 were hand-seeded at fairly low rates with non-native grasses and legumes, primarily white bent Agrostis alba, tall fescue Festuca arundinacea, Chinese lespedeza Lespedeza cuneata and red clover Trifolium pratense, and also the native locust tree Robinia pseudoacacia. No efforts were made to replace soil.

Sites reclaimed between 1972 and 1977 were hydroseeded in a wood mulch slurry with plants used previously and other non-native grasses and legumes, foxtail bristle-grass Setaria italica, rye Secale cereale and melilot Melilotus spp. Weymouth pine Pinus strobus, native to south-east USA, was planted on top of the slopes.

The sites reclaimed in 1980-87 were revegetated to meet legal requirements including restoring original contours and providing for about 1,000 trees/ha and a target of 90% herbaceous cover after 5 years. They were seeded at high rates with species as those of the earlier reclaimed sites, plus additional non-native grasses: cock's-foot Dactylis glomerata and timothy Phleum pratense, and legumes: bird's-foot trefoil Lotus corniculatus and white clover Trifolium repens. P.strobus were planted throughout the sites.

Vegetation surveys: Vegetation was sampled on 16 sites in August 1992, and the remaining four in August 1993. Nineteen of the 20 sites were resurveyed in 1999. One of the 1962-67 sites was not resurveyed as it had been remined. Vegetation was sampled as follows:

i) herbaceous layer (<0.75 m tall) - in August, the total percentage cover and percentage cover of individual herb species were recorded in 16, 1 m² quadrats. Quadrats were distributed along four transects perpendicular to the slope and separated by a distance of 10 m.

ii) shrubs (0.75 - 2 m tall) - from June to early July, shrubs were sampled in eight 4 x 4 m quadrats spaced along the transects at 10 m intervals. Total percentage cover and percentage cover of individual species were estimated in the shrub layer.

iii) trees (>2 m tall) - from June to early July, trees were sampled in eight 10 x 10 m quadrats, again distributed along the transects. The composition of the canopy was quantified by measuring the diameter at breast height (dbh) of trees rooted in the quadrat.

A total of 159 plant species were found on all sites; 92 native herbs, 39 native woody species, 22 non-native herbs and six non-native woody species. Native, naturally colonizing species comprised the vast majority of both herb and woody species at all sites. Herbaceous species richness was similar on all sites, whereas woody species richness was higher in the forest reference sites compared with the reclaimed sites.

Vegetation community composition on reclaimed sites continued to progress towards that of the forest reference sites between the two sampling periods, but composition even on the oldest sites (reclaimed > 35 years prior) still differed substantially from the reference sites.

Herbaceous cover was higher and tree basal area was lower in reclaimed sites compared with forest sites at the first sampling period but these differences were less pronounced by the second sampling period.

The overall composition of the older reclaimed sites was similar to the forest sites, however, as with a number of previous studies of long-term recovery on highly disturbed sites, a number of less common forest specialist species still had not colonized even the oldest reclaimed sites.

Conclusion: These results suggest that goals for short-term and long-term vegetation recovery of such sites may conflict, e.g. planting with aggressive non-native ground cover species to minimize short-term erosion may have slowed long-term recovery on the sites studied. Widespread planting of Pinus strobus had not reduced plant species richness but this can be expected as the trees mature and the canopy closes.

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