Long term comparison of post mining site restoration with unassisted forest recovery

We evaluated the long-term development, ecological performance, and carbon dynamics of reclaimed and unreclaimed post-mining forest sites on coal spoil heaps in northwestern Czech Republic. Using historical aerial photographs, field inventories, and repeated surveys spanning 12–90 years, we characterized spontaneous forest succession and compared it with alder-reclaimed sites. Early successional stages on unreclaimed sites were dominated by pioneer species, primarily silver birch (Betula pendula), goat willow (Salix caprea), and aspen (Populus tremula), with Norway spruce (Picea abies) establishing naturally in intermediate stages. A 90-year-old site approached climax forest, hosting 21 woody species dominated by pedunculate oak (Quercus robur) and European beech (Fagus sylvatica).

Tree density and biomass were initially higher on reclaimed sites however in intermediate stages of sucession tree biomas in unreclaimed sites exceed reclaimed ones. Ecosystem measurements using eddy covariance showed that unreclaimed sites functioned as stronger carbon sinks (−256 g C m⁻² yr⁻¹) than alder-reclaimed sites (−166 g C m⁻² yr⁻¹).  Unreclaimed sites supported more favorable conditions for the establishment, growth, and mycorrhizal colonization of climax species namely Oak, beach and spruce, linked to lower soil pH, higher organic matter, and richer soil biota. Repeated surveys revealed sustained natural recruitment and relatively low mortality rates of climax species which ensure succesful establishment despite being several kilometers from seed sources.

Overall, spontaneous succession produced structurally and functionally diverse forests with comparable or superior long-term performance and carbon sequestration relative to conventional reclamation, highlighting the ecological value of unassisted forest recovery while suggesting cautious use of nitrogen-fixing plantations.