Selecting topsoil substitutes for Forestry mine soils

The Forestry Reclamation Approach is a five-step system for reclaiming mined lands to forests. Step 1 of the FRA involves creating a suitable rooting medium for good tree growth using topsoil, weathered sandstone and/or the best available material. Several types of overburden types can be selected to place on the surface as growth media. These spoil types include weathered brown sandstone and unweathered rock materials including sandstones, siltstones, shales, and mixtures of these materials. When sufficient topsoil is not salvageable, reclamation scientists often recommend that, when available, weathered sandstone should be considered as the "best available" topsoil substitute material. Here, we review the scientific evidence that supports such recommendations. Several studies have shown that tree survival was not significantly different among spoil types. Weathered brown sandstone, unweathered gray sandstone, siltstone and shale materials all produced good tree survival (>70%) when compaction and competitive ground covers were reduced. However, growth for most trees (as measured by height, diameter, and volume) was usually significantly greater in weathered brown materials than in unweathered sandstones, siltstones, shales, and mixed spoils. At one site in West Virginia five years after planting, a 10-fold difference in tree volume was found between these two spoil types. Similar results have been found with other studies across Appalachian surface mines. Based on the results of studies summarized herein, the use of weathered brown sandstone is generally recommended, along with topsoil materials when available, to be placed on the surface on sites where hardwood tree species are being planted for forestry post-mining land uses. Weathered brown sandstone spoil materials have a pH, soluble salt content, fine earth content well suited for trees, and sufficient nutrient supplying and water holding capacity that results in superior tree growth compared to other spoil types. The brown sandstone material more closely resembles the native forest soil than the unweathered gray materials.