Effect of soil depth and topographic position on plant productivity and community development on 28-year-old reclaimed mine lands

Abstract

Reclamation research has shifted from short- to long-term assessment of mine land reclamation management strategies, wherein previously established study sites are revisited. In this study, we assessed long-term (28 y) relations among reestablished plant communities (production and diversity), replaced soil depth following mining (0.2 to 1.4 m [0.7 to 4.6 ft]), and restored slope position (5% north slope, 2% south) for three different subsoil types (A, B, C; characterized by 43%, 23%, and 14% clay, respectively) on a previously established soil wedge experiment in North Dakota (Merrill et al. 1998). Nonnative seeded species such as crested wheatgrass (Agropyron cristatum) and smooth brome (Bromus inermus) had close to 50% persistence after 28 y, while less aggressive seeded species, such as Russian wildrye (Psathyrostachys juncea) and alfalfa (Medicago sativa), were more susceptible to invasion by other species leading to greater plant community diversity (Shannon's Diversity Index [H′ = 1.348 and 1.717, respectively]). The most significant plant productivity response to soil depth/topographic position was observed for subsoil C on the south facing 2% slope (r² = 0.43; p = 0.03). The two soil parameters measured in this study (electrical conductivity and pH) indicated mine soil profile development through time for both slope position and subsoil type. Specific relations observed in this long-term study were somewhat more difficult to identify compared to earlier short-term studies conducted on this site, providing strong evidence that replaced soil depths should be determined based on soil stabilization and initial establishment of diverse, sustainable plant communities to reduce invasion of undesirable plant species.