Hardwood reforestation on post-mined land under varying soil replacement strategies in the eastern interior region

Jessica Hannah Johnston, Purdue University

Abstract

Approximately two million hectares of land in the U.S. have been impacted by surface coal mining and subsequent reclamation. Soil replacement strategies follow standards set by state and federal regulations; however, permits allow for new techniques, such as the soil replacement method studied in this project, in order to improve the quality of the land. A new strategy, which involves dumping soil in overlapping piles with minimal equipment compaction, has been studied in the Appalachian coal region on a range of site conditions. However, this approach has not been evaluated in the Eastern Interior region, which includes Indiana. This study assessed the relationships of soil physiochemical and biological conditions on plant survival, growth, and root development by investigating growth responses of seedlings planted on standard graded (GR) plots and those planted on loosely dumped (LD) soil. The study, located on a reclaimed mine site in southern Indiana, used a split plot design. A total of 3200 seedlings of four hardwood species, northern red oak ( Quercus rubra L.), white oak (Quercus bicolor W.), Shumard oak (Quercus shumardii B.), and American chestnut (Castanea dentate B.), were used. Soil physical properties of the LD and GR soils showed significant treatment effects. Bulk density, moisture retention and porosity of the LD soil were favorable for plant growth. The GR soil had a significantly higher bulk density (1.74 g/cm3) compared to the LD soil (1.54 g/cm3) resulting in root impairment. The chemical properties of the LD and GR soils showed little variation and had low fertility status, organic carbon contents, and cation exchange capacities consistent with that of a subsurface soil. The presence and activity of soil microorganisms measured through microbial biomass (MB) and fluorescein diacetate (FDA) hydrolysis were low and reflected the poor soil quality with slight treatment differences. Seedling survival was significantly higher in the LD treatment compared to the GR treatment at the end of the second growing season. Above ground growth of the four hardwood species did not favor one soil replacement method over the other as few treatment effects were observed. A few exceptions to this generalization were observed which favored the LD treatment: average plant biomass significantly increased and plant water potential significantly decreased (less water stressed) in the LD treatment. The similarities in above ground growth among treatments is attributed, in part, to the short duration of the study (17 months) which may not be a sufficient amount of time for differences in above ground growth to manifest themselves. In contrast, the below-ground growth parameters indicate that the method of soil replacement influenced root morphology and architecture due to the difference in soil properties. Increased lateral and tap root dry weights, root volume and projected root area (measured by WinRHIZO) were observed in seedlings grown on the LD treatment. It is likely that bulk density was the main root-restricting factor. American chestnut seedlings ranked highest in root and shoot parameters, as well as plant water potential; yet this species ranked lowest in survival and had the greatest amount of dieback. In contrast, Shumard oak seedlings generally ranked second or third in root and shoot parameters; and yet had the highest survival rate and largest increase in lateral root dry weight compared to all other species. Overall, this study showed that seedling survival and growth was favorable on the LD treatment. The below ground root responses measured with traditional or WinRHIZO analyses were clear indicators that the seedlings favored the LD treatment. In general, above-ground growth parameters were not sensitive indicators of growth over the 17-month study period, whereas below-ground root parameters proved to be sensitive indicators of seedling growth.

Degree

M.S.

Advisors

Schwab, Purdue University.

Subject Area

Forestry|Soil sciences

COinS