Forest Floor Protection: The Critical Defense Against Post‐Harvest Soil Carbon Loss

Understanding the dynamics of soil carbon accumulation and loss following forest harvest is crucial for sustainable forest operations in western Canada. However, the region's diverse climates and forest types complicate broad generalizations regarding disturbance impacts. We synthesized 20 years of soil carbon stock (SCS) data from the British Columbia Long‐Term Soil Productivity (BC‐LTSP) study with increasing soil compaction and organic matter removal treatments across 12 sites spanning four biogeoclimatic zones. Forest floor (organic) and mineral soil (0–20 cm) SCS were measured pre‐harvest and at 5, 10, and 20 years post‐harvest. The study evaluated SCS dynamics under three organic matter removal treatments: stem‐only harvesting (OM1), whole‐tree harvesting (OM2), and an extreme treatment that included both harvest residue and forest floor removal (OM3). Simultaneously, the impact of three compaction treatments was assessed: no compaction (C0), moderate compaction (C1), and heavy compaction (C2). When the forest floor remained intact during harvest, there were insignificant forest floor carbon losses (5%) by Year‐20 with a simultaneous increase in mineral soil (14%). Stem‐only harvesting (OM1) maintained a larger (15%) SCS pool in the forest floor compared to whole‐tree (OM2) harvesting ( p = 0.07). There was a substantial (52%) loss in total soil carbon (organic + mineral) from the OM3 treatment by year 5 and SCS was still 33% below pre‐harvest levels at Year‐20. There was no difference between the C1 and C2 compaction levels with no measurable effect on SCS. Protecting the forest floor from additional harvest disturbance resulted in minimal impact on soil C pools.