Background <p>In forest ecosystems, the decomposition of deadwood, primarily driven by fungal communities, constitutes a fundamental ecological process. The initial phase of deadwood decomposition is particularly critical, marked by significant shifts in fungal community composition. However, the assembly mechanisms, key drivers shaping wood-inhabiting fungal communities and whether fallen logs degradation has home-field advantage or not during this phase remain inadequately understood.</p> Methods <p>This study focused on this crucial yet understudied initial decay phase by establishing a chronosequence of decomposition initiation and quantifying differential decay rates between Korean pine (<i>Pinus koraiensis</i>) and white birch (<i>Betula platyphylla</i>) under “home” versus “away” field conditions.</p> Results <p>Notably, Korean pine logs exhibited slower decomposition rate compared to white birch, accompanied by divergent successional trajectories in their respective fungal communities. No significant home-field advantage was observed in either fungal community composition or structural assembly during log decomposition. Correlation analyses identified nitrogen content within the logs as a key limiting factor regulating fungal communities in both tree species, with distinct adaptation thresholds and ranges identified among taxa. Fungal community assembly was governed by a combination of stochastic processes, dispersal limitation, and homogenizing selection, reflecting a complex, multidimensional mechanism.</p> Conclusions <p>By elucidating fungal-mediated decomposition dynamics, this study provides critical insights into the degradation mechanisms of forest deadwood and its ecological functions in biogeochemical cycling, while offering a novel perspective for interpreting forest ecosystem succession.</p>