2022 Volume 27 Issue 1-2 Pages 3-13
Coal mines have long supported industries worldwide. Coal mine spoil heaps are unstable piles of waste coal or lignite that collapse easily. Therefore, to increase the safety of former coal mines, it is important to stabilize spoil-heap slopes. Vegetation recovery stabilizes slopes by preventing soil-surface erosion. This study clarified the effects of various factors on vegetation recovery and provides guidelines for vegetation recovery and its management. The study sites were 15 spoil heaps in Sorachi General Promotion Bureau, Hokkaido, Japan. To investigate factors affecting vegetation recovery, we examined the effects of the percentage of surrounding forest, topographic wetness index, slope, percentage of landform alteration, presence or absence of afforestation, number of years since the coal mine closed, vegetation cover, and average tree height. The results showed that the number of years and slope affected vegetation recovery and implied that the vegetation on a spoil heap is likely to change to woody vegetation over time, after abandonment of the mine. A negative effect of the mean slope on vegetation recovery was prominent for slopes > 25°. This is likely to be related to the angle of repose of the soil. A greater mean slope leads to loss of seeds and inhibition of plant establishment due to increased surface erosion. The vegetation cover ratio on spoil heaps with an average slope ≤ 25° can reach 75% after 42 years through natural succession, whereas revegetation practices are required to restore vegetation on slopes > 25°. This serves as a reference angle for a revegetation guideline, for vegetation recovery at coal-mine sites.
