Effects of Silvicultural Treatments and Soil Properties on the Establishment and Productivity of Trees Growing on Mine Soils in the Appalachian Coalfields
Casselman, Chad N.
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Coal has been and will continue to be an important energy source in the U.S. for the foreseeable future. Surface mining for coal is one of the methods employed to extract this resource from below the ground. The process of surface mining removes native topsoils and any native vegetation that was support by these native soils. In the Appalachian coal-producing region of the United States, the pre-mining landscape is predominantly forested. Prior to the Surface Mining and Reclamation Act of 1977 (SMCRA), surface mined lands were commonly reclaimed to forests. Subsequent to the passage of SMCRA, reforestation of surface mined lands has decreased. As a result, thousands of hectares of land that were forested prior to mining are being reclaimed using grasses and legumes. This is done in spite of the fact that the SMCRA requires that land be reclaimed to an â equal or higher land use.â The decline of reforestation stems from two main issues, namely: (1) reclaiming land to pasture is an easy and low-risk way for mining companies to obtain bond release; and (2) SMCRA reclamation requirements have led to unfavorable conditions for tree establishment and growth. Recent interest has been shown in reverting these surface mined lands that have been reclaimed to pasture back to forests for reasons related to the environmental, economic, and carbon sequestration benefits that forests are believed to have when compared to pasture land. It is believed that forests can be established on existing reclaimed pasture land through the use of silvicultural treatments, that mature stands of trees growing on surface mines will respond to treatment similarly to stands growing on native soils, and that mature stands growing on relcaimed surface mines have different soil properties controlling their growth than those that have been found for younger stands. The purpose of this investigation was to understand the biological feasibility of restoring forests on post-SMCRA surface mined lands in the Appalachian coalfields reclaimed to pasture and to understand the productive potential and factors governing the productive potential of pre-SMCRA surface mines supporting mature forests in an attempt to show the benefits of reclaiming these lands with forests. A 3x3x3 factor random complete block design was used to assess first-year survival and growth of three species assemblages under three levels of silvicultural treatment intensity at each of three study sites having different site characteristics. The native hardwood species assemblage was found to have the best survival across all three sites, with 80 and 85% survival for sites with spoils derived from shale and oxidized sandstone, respectively. White pine generally had the lowest survival of all species and ranged from 27% across treatments on siltstone spoils to 58% across treatments on oxidized sandstone spoils. Hardwood and white pine grew little over the first year, ranging from -3.7 to 8.9cm in height compared to hybrid poplar, whose height growth ranged from 22.4cm to 126.6cm. Response to silvicultural treatment was variable by site and species, but weed control in combination with tillage generally resulted in the highest survival. Greatest height growth (126.6cm) occurred on the oxidized sandstone spoil, where hybrid poplar was treated with weed control plus tillage in combination with fertilization. Hybrid poplar was found to have the greatest growth after one year compared with the hardwood and white pine and also had the greatest height growth at each level of silvicultural intensity for all sites. This superior growth should give hybrid poplar an advantage over the others used to revert these grass lands back to forests, as the amount of height growth observed (>50cm over one year in the weed control plus tillage treatment at all sites) may be enough to ensure that these trees will not succumb to aggressive competing vegetation without further weed control. The results of this study show that based on first-year data, reforestation of these lands does appear to be biologically feasible, given the species and treaments used. In an attempt to quantify the productivity of a 26-year-old white pine stand established pre-SMCRA, a random complete block experiment was used to compare the response to a thinning that occurred in this stand at age 17. Site index of the stand was found to be 32.3m at base age 50, indicating that this is a very productive stand. Neither stand volume nor stand value was statistically different at age 26 between treatments with volumes and values ranging from 290m3ha-1 and $5639 ha-1 to 313 m3ha-1 and $5478 ha-1 for the thinned and unthinned treatments, respectively. The difference in mean breast-height diameter, however, was significant at age 26, and this was confirmed by a significant difference in a repeated measures analysis of annual diameter data for these treatments (P < 0.0001). Projection to age 30 revealed that both stand volume and value would be significantly higher in the thinned treatment by margins of 8.7 m3 ha-1 and $2457 ha-1. Regression analysis of soil data within the observed rooting depth of the trees from this stand indicated that nitrogen mineralization index, bulk density, sand percentage of the fine soil fraction, and percentage of oxidized sandstone in the soil profile were the most important variables in determining the standâ s productive capacity (R2 = 0.7174). It was also found that of the five different spoil types encountered in the stand, the oxidized sandstone spoil had the most favorable physical and chemical properties for tree growth. Common root-restricting layers were found to have high soil density or increased levels of soluble salts. It has been shown that reclaimed surface mines can grow productive forests if the appropriate spoil materials are returned to the surface in sufficient depth. It has also been shown that surface mined lands reclaimed to pasture can be successfully reforested using silvicultural treatments to ameliorate unfavorable conditions for tree establishment and growth, though these treaments may not be cost-effective, and the success of these treatments was variable based on the soil characteristics of each site.
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