Tracing soil redistribution rates following harvesting in northern hardwood forests using 239+240Pu isotopes

Accelerated soil erosion and deposition pose major threats to soil health and ecosystem services in forested landscapes. Clear-cutting, particularly whole-tree harvesting (WTH), in which the stem and crown are removed from the site, intensifies erosion processes. At the Hubbard Brook Experimental Forest (HBEF) in New Hampshire, US, WTH was conducted between 1983 and 1985, and several studies have examined its ecological impacts; however, no study has evaluated its effect on soil redistribution. Here, we aimed to 1) quantify erosion and deposition rates along slopes following WTH using 239+240 Pu, 2) evaluate soil morphological changes nearly 40 years after harvesting, and 3) test the suitability of 239+240 Pu as a tracer of soil erosion and deposition processes in acidic sandy soils. The results revealed that WTH increased soil redistribution: mid-backslope soils showed erosion rates of −6.8 ± 3.33 t/ha/y (Profile Distribution Model - PDM) and − 8.9 ± 3.45 t/ha/y (MODERN), toeslope soils exhibited deposition rates of 2.06 ± 2.56 t/ha/y (PDM) and near zero (MODERN), and upslope soils displayed values near zero (PMD) or limited erosion (MODERN). Thinner organic horizons were the only remaining morphological sign of disturbance, indicating incomplete forest-floor recovery. 239+240 Pu depth profiles showed strong near-surface retention with only limited lateral subsurface migration, confirming the suitability of 239+240 Pu for tracing erosion processes in acidic sandy soils. These findings evidenced that WTH leaves a long-term geomorphic imprint, highlighting the need to consider erosion processes for sustainable forest practices, soil management, and carbon storage.