Despite five years of hazard tree investigation and mitigation (Potential Hazard Tree monitoring and hazard tree removal) from 2020 to 2024, the incidence ratios of hazard trees (HTs) and Potential Hazard Trees (PHTs) along the Alishan Forest Railway corridor (spanning subtropical, warm temperate, and temperate zones) have not exhibited a significant downward trend. This study aims to investigate the impacts of climate zones, succession, and functional groups on hazard tree occurrence and to further predict the incidence ratios of hazard trees. We employed Generalized Linear Models (GLMs) and structural defect frequency to evaluate these interactions. The significance of the impacts is ranked as follows: functional group > succession regeneration > climate zone. Incidence was highest in subtropical (S) and warm temperate (W) zones (S ≈ W > T), and significantly greater for secondary succession (SS) areas compared to Planning Plantation (PP). Crucially, heliophilous species (H + P; small-to-medium pioneer and canopy heliophilous species) contributed significantly more to hazard incidence than non-heliophilous species (MT + T; mid-shade-tolerant and shade-tolerant species). Model predictions identified (H + P) + SS + S as the highest-incidence ecological combination, while (MT + T) + PP + T was the lowest. Structural defect relative frequency analysis revealed that the fast-growth strategy of H + P species fundamentally compromises their biomechanical stability, resulting in significantly higher defect frequencies compared to MT + T species. Furthermore, continuous corridor disturbances maintain a persistent light environment that perpetually recruits these H + P species via secondary succession. To effectively manage the incidence of HT and PHT, future mitigation measures must prioritize Planning Plantation (PP) using non-heliophilous (MT + T) species selected within their appropriate ecological amplitudes.
Chan et al. (Tue,) studied this question.