Age-matched benchmark comparisons show region-dependent forest recovery on legacy industrial sites

Disturbances associated with energy development can create persistent vegetation and soil legacies that challenge forest reclamation by slowing successional recovery. Benchmark ecosystems are essential for evaluating recovery progress, but they must reflect both ecological variation and stand age to provide meaningful reference conditions. We applied an age-matched benchmark approach, comparing indicators of forest development between 85 reclaimed legacy well sites that underwent re-vegetation treatment (soil decompaction, herbicide application, and tree planting) and 38 post-harvest benchmark sites harvested contemporaneously with these interventions. Sites were distributed across three boreal natural regions, reflecting an elevational gradient of warmer-drier to cooler-moister conditions, in Alberta, Canada, and vegetation was sampled approximately 16 years after the most recent intervention. Legacy well sites exhibited higher herbaceous cover than benchmarks, with greater abundance of non-native forbs and grasses and lower abundance of native forbs. Well sites also had lower stem densities, basal areas, and model-projected stand volumes than benchmarks. These departures were strongest in low-elevation, warmer-drier regions, suggesting the potential influence of greater abiotic and biotic constraints on recovery. In colder-moister regions, both herbaceous composition and tree regeneration more closely resembled benchmark conditions, suggesting that favorable environmental regimes coupled with improved establishment practices can offset legacy effects. Furthermore, post-harvest benchmarks performed consistently across natural regions, indicating that region-specific certification thresholds may not be necessary. Overall, our results indicate that sustained vegetation control and adaptive planting strategies tailored to local environmental regimes will be critical for restoring long-term forest structure and function on legacy-impacted well sites.