Deadwood mitigates the decline in soil multifunctionality in canopy gaps

Worldwide, intensified timber harvest and frequent climate extremes are reshaping forest structure by increasing tree mortality and canopy opening, threatening terrestrial biodiversity and ecosystem sustainability. In unmanaged forests, natural disturbances result in both canopy gap formation and deadwood addition, whereas timber harvesting creates forest gaps while removing most deadwood. However, how these disturbances and management practices affect ecosystem functioning, especially of the belowground system, remains little understood. Here, we reconstructed 116 soil animal food webs in a full-factorial experiment manipulating forest gaps and deadwood addition. We quantified energy fluxes of soil food webs as an integrative measure of belowground ecosystem multifunctionality and investigated their network architecture two years after establishment of the experiment. Forest gaps reduced total food web energy fluxes by 13.4%, decreased network connectance and shifted energy flow towards the bacteria-dominated “fast” channel, indicating simplified soil food webs, impaired ecosystem multifunctionality, and reduced energy retention belowground. However, compared to gaps without deadwood the presence of deadwood in gaps increased total energy flux by 37.4%, primarily through enhanced fungivory and wood-feeding pathways, and restored network connectance and cycling rate to the levels coclosed-canopy forests. Our results demonstrate that deadwood acts as a key structural component that mitigates the detrimental effects of canopy gap formation on belowground ecosystem multifunctionality, underscoring deadwood retention after timber harvest as a practical strategy to safeguard soil functioning in a more disturbance-prone future.