Comparison of Ecosystem CO₂ Fluxes Between Restoration and Unassisted Succession in Mid-Stage of Recovery After Coal Mining

Forest plantation is a common method for restoring post-mining sites, but in suitable conditions, forests can also develop spontaneously on unreclaimed sites. Despite this potential for natural forest recovery, no direct measurements have been conducted to compare carbon fluxes between reclaimed and spontaneously developing forests in post-mining areas, particularly those degraded by coal mining. To address this, we measured the net ecosystem exchange (NEE) using the eddy covariance (EC) technique in 2019 at two post-coal mining sites in northwestern Czechia: (i) a reclaimed site, restored with nitrogen-fixing alder plantation (Alnus glutinosa), and (ii) an unreclaimed site, developing spontaneously with fast-growing species dominated by Salix caprea, Betula pendula, and Populus tremula. The unreclaimed site, dominated by naturally regenerating willow, showed a carbon sink of −256 g C m−2 yr−1 with gross primary productivity (GPP) of 1153 g C m−2 yr−1 and ecosystem respiration (Reco) of 897 g C m−2 yr.−1. In contrast, the reclaimed site, restored by alder, exhibited a carbon sink of −166 g C m−2 yr−1 with GPP of 1469 g C m−2 yr−1 and Reco of 1303 g C m−2 yr.−1. The unreclaimed site exhibited a stronger NEE (p > 0.05) due to lower Reco (p < 0.05). In contrast, the reclaimed site showed high positive NEE values, particularly in the fall, which reduced its annual carbon sink, highlighting the importance of fall emissions on the annual NEE balance. Overall, our results emphasize that natural vegetation can achieve stronger NEE in Central Europe after coal mining.