REVEGETATION TRENDS AND LESSONS AT TWO MONTANA COAL MINES BASED ON 20 YEARS OF MONITORING

Abstract

Abstract: Bighorn Environmental Sciences monitored revegetation at Spring Creek Coal Mine (SCCM) and Decker Coal Mine (DCM) in semiarid southcentral Montana for 20 years using consistent transect locations and methods. Measurements include canopy coverage, air-dried peak standing crop (PSC), and shrub density. About 30 SCCM fields were old enough to evaluate temporal trends. Findings include: • Ten years after seeding, post-mine perennial productivity and canopy coverage were trending upward and exceeded both performance standards and pre-mine vegetation. • Shrub density declined in about 4/5s of fields. Meeting the shrub density standard of 5,740/ha for wildlife habitat, the primary post-mine land use, is a major revegetation challenge. • Rosana western wheatgrass tripled in relative cover by the conclusion of monitoring. It combines environmental suitability and vigorous rhizomatous spread. Introduced sheep fescue spread even more abundantly, quadrupling relative cover from the early years to one decade or more later, also spreading to adjacent fields. • Cheatgrass, which replaces annual forb weeds in unsatisfactory seedings, showed no net temporal trend. • The explosion of the first-year kochia impairs seeding success through interference competition. Prevention requires mine-wide effort. Seeding into annual weeds or litter has not worked, requiring chemical weed control and litter removal before interseeding. The first seeding opportunity is the best. • Shrub seedings are far more successful on suitable spoil than on topsoil. However, some spoil meeting the chemical-physical suitability criteria does not support satisfactory revegetation. Scoria can be a fine shrub and diversity substrate or disappointing. • Heavy-seeded Chenopod shrubs can be established through drill seeding even among vigorous, competitive grasses. • Light-seeded sagebrush establishes best when seeded apart from the heavy-seeded plants. • The most prevalent contribution of direct-haul coversoil to revegetation is weeds, not native perennials.