Abstract/Summary

Much of the remarkable plant species diversity of the Southwest Australian Floristic Region can be attributed to high diversity of the understorey in its forests and woodlands, including 400–600 understorey species per km2 in the Northern Jarrah Forest alone. Consequently, returning species diversity is a key challenge for postmining ecological restoration in the region. Each year, Alcoa of Australia undertakes restoration of mined areas within the Northern Jarrah Forest with a goal of returning a self-sustaining jarrah forest ecosystem. To meet this goal, it is important to understand long-term (i.e. > 20 years) trajectories of vegetation development and the restoration practices that direct species diversity outcomes. Here, we report the results of several experiments, the oldest of which is 45 years of age, which together demonstrate significant longer-term effects on understorey species diversity of restoration practices determining initial conditions including topsoil handling, fertiliser application, seeding rates of large legumes, and tree (overstorey) species stocking rates. Our research highlights (1) that ‘historical contingency’ can determine the trajectory of jarrah forest restoration and (2) that longer-term studies are critical as they give a different, sometimes conflicting, perspective to short-term datasets. Notably, after 27 years, we found an inverse relationship between plant cover and P fertilisation, where plant cover was highest in the in the absence of P fertiliser and lowest at the uppermost P amendment rate. We also found that the long-accepted Initial Floristics Model of succession does not fit well with our data. Our overall findings are likely useful to restore understorey diversity to woodlands, forests, and abandoned farmlands elsewhere in the region.