Surface mines show little progress towards native species forest restoration following 35 years of passive management after initial reclamation

Restoration techniques using passive management rely on natural plant community succession after reclamation to return disturbed areas to native ecosystems. This approach is often used in areas affected by mining activity, but effectiveness is variable and depends on the ability of native plants to establish in highly degraded soil and outcompete invasive species. We evaluated the restoration progress of three former surface mines where activity had exposed alkaline glacial till parent material. The mines underwent reclamation (grading, soil compaction, and planting fast-growing herbaceous species) followed by passive management for 7, 28, and 35 years. At the time of initial restoration planning in the 1980s, native woody species were expected to recolonize the site within 10–20 years. Treating the sites as a chronosequence, we observed that woody vegetation increased inconsistently over this 35-year timespan. Most of the woody plants present today are invasive species (Elaeagnus umbellata and Rhamnus frangula) that are counterproductive to reestablishment of native forest. However, results were not entirely negative, with increased overall native species and decreased exotic species in the older sites, and plant community composition changing somewhat consistently over time. This suggests that succession has been slowed rather than completely arrested, and native herbaceous plants are establishing. The progression of restoration appears to be far slower than expectations during initial planning. Furthermore, native woody plants struggle to establish, whereas invasive woody plants are thriving, raising doubts that passively managed succession can lead to the desired outcome of a native species forest in this significantly degraded habitat.