Evaluation of Growth and Survival of Hardwood Trees on Brown and Gray Sandstone

Evaluation of Growth and Survival of Hardwood Trees on Brown and Gray Sandstone Lindsay M. Wilson-Kokes Deciduous forests in the Appalachian region have been greatly disrupted due to surface coal mining since the 1930’s. After the passage of the Surface Mining Control and Reclamation Act (SMCRA) in 1977, coal mine operators began planting a variety of grasses and legumes as a fast and economical way to re-establish a permanent vegetative cover in order to meet erosion and site stabilization requirements. However, soil compaction and competitive forage species have arrested the re-colonization of native hardwood tree species on these reclaimed sites. In an effort to evaluate tree growth on selected spoils and determine the effects of compaction, three 2.8-ha experimental plots were established at Catenary Coal’s Samples Mine in Kanawha County, West Virginia. Two plots were constructed of weathered brown sandstone and the third plot was constructed of un-weathered gray sandstone. Half of each plot was compacted while the other half was non-compacted. Each plot was hydroseeded with a low competition herbaceous cover and planted with eleven hardwood tree species. Soil chemical properties and tree growth have been measured each year since 2005. After eight growing seasons, average tree volume index was nearly ten times greater for trees grown in the brown sandstone treatments, 3853 cm 3 , compared to 407 cm 3 in gray sandstone. Trees growing on compacted treatments had a lower mean volume index, 2281 cm3, than trees growing on non-compacted treatments, 3899 cm3. Average pH of brown sandstone was 5.2 to 5.7 while gray sandstone was 7.9. The gray sandstone has continued to resist breakdown and had much lower fines content (40%) compared to brown sandstone (70%), which influenced nutrient and water-holding capacity. After eight years, brown sandstone showed significantly greater tree growth and survival, and is a more suitable topsoil substitute than gray sandstone on this site. The second study site was a 2.8-ha experimental plot established at Arch Coal’s Birch River mine in Webster County, WV. Half of the plot was constructed of weathered brown sandstone and half was constructed of unweathered gray sandstone. Bark mulch was applied to a small area covering both sandstone types and the ends of the plot were hydroseeded with a low competition herbaceous cover, resulting in eight soil treatments. The plot was then planted with twelve hardwood tree species and soil chemical properties and tree growth have been measured each year since 2008. After six growing seasons, average tree volume index was consistently higher for trees grown on brown sandstone (5,333 cm 3 ) compared to gray sandstone (3,031 cm 3 ). Trees planted on treatments with bark mulch outperformed trees on non-mulched treatments (volume index of 6,187 cm 3 vs. 4,194 cm 3 ). Hydroseeding with a tree-compatible mix produced greater ground cover (80% vs. 45%) and resulted in greater tree volume index than nonhydroseeded areas (5,809 vs. 3,403 cm 3 ). Soil chemical properties of mulched treatments showed little similarity to those of the underlying sandstone, which suggests the bark mulch overcame the poor characteristics of the gray sandstone parent material for tree growth. The average pH of brown sandstone mine soils was 5.0 to 5.4 and gray sandstone mine soils averaged pH 6.9 to 7.7. The non-mulched gray sandstone material has resisted breakdown and weathering, and still had a high pH and low percentage of fines after six years resulting in slow growth of trees. The mulch treatment on gray sandstone resulted in tree growth similar to brown sandstone alone. After six years, brown sandstone showed about double the growth of trees compared to gray sandstone, and bark mulch was a successful amendment that improved tree growth. Tree leaves were also collected from three tree species growing on non-hydroseeded treatments at the Birch River mine for nutrient analysis and compared to tree leaves of the same species collected from an un-mined forest within the permitted area of the Birch River mine. Foliar phosphorus was lower in all three tree species on all non-hydroseeded treatments compared to trees growing in the unmined forest. Other nutrients such as potassium were consistently low on the gray sandstone for all species. While many trees growing on these soils, both reclaimed and unmined, are obtaining sufficient amounts of nutrients for growth, the brown sandstone demonstrated many foliar and soil values which were similar to values measured on the unmined forest while the gray treatment seemed to be providing fewer nutrients for adequate growth.