Long-term plant community development on topsoil treatments overlying a phytotoxic growth medium

The application of topsoil over phytotoxic mine waste materials is often th e most effective method for establishing plant communities and protecting t hese communities from the inimical properties of such,waste materials. Howe ver, long-term data on the effectiveness of this type of remediation, as we ll as on cultural treatments used to entrance vegetation establishment on t opsoil cover treatments, are lacking. Therefore we evaluated long term plan t community development on study plots where 60 cm of Paraho retorted oil s hale was revered by various depths of topsoil. The study plots were drill s eeded with native, introduced, or a combination of native and introduced sp ecies, and fertilized dth one of three rates of nitrogen (N) and phosphorus (P) fertilizer following construction of the plots in 1977. Data collected 20 Jr after seeding showed that total aboveground biomass was greatest on deeper topsoil depths and on plots seeded with introduced plant species. Ho wever, when considering the interaction between these two variables, we fou nd that native species were as productive as introduced species on deeper t opsoil depths and on the control. Relative plant species composition and pl ant species richness were greatly influenced by seed mixture treatments. Pl ots seeded with a particular seed mixture in 1977 were still highly dominat ed by those species originally seeded, and native seed mixture plots were m ore species rich than introduced seed mixture plots. Chemical analysis of t he soil covers and underlying retorted shale suggests that leaching process es have moderated the once adverse chemical characteristics of the retorted shale.