FOREST ECOSYSTEM RECOVERY IN 15-YEAR-OLD HYBRID ASPEN (Populus tremula L. x P. tremuloides Michx.) PLANTATIONS ON A RECLAIMED OIL SHALE QUARRY

The development of forest ecosystem components (tree layer, understory vegetation and topsoil) in a reclaimed oil shale quarry was evaluated based on the repeated monitoring of sample plots 5 and 15 years after afforestation with hybrid aspen. Trees had been planted directly on levelled quarry spoil (site group A1) or on quarry spoil with restored topsoil (site group A2). The reference group included hybrid aspen plantations on former arable land (site group B1). Over a decade, the relative tree growth had been slower on A1 and A2 compared to B1. Soil reaction (pH(KCl)) had decreased and soil total nitrogen (N-tot) had increased on A1. High pH(KCl) value and low stocks of N-tot, phosphorus (P), manganese (Mn) and boron (B) restricted tree growth on A1. The properties of soil, as well as understory vegetation on A2 were similar to those on B1, which indicates that restored topsoil ensured the faster development of A2 towards the Hepatica forest type.