Multiple processes jointly determine ecological uniqueness across forest plant life‐forms in Northeast China

Abstract Aim Ecological uniqueness is an essential component of biodiversity. However, the mechanisms underlying patterns of ecological uniqueness remain unresolved. This study aims to assess the relative importance as well as interactive roles of four hypothesized processes (regional climate filtering, local environmental filtering, biotic heterogeneity and disturbance intensity [DI]) in shaping ecological uniqueness across three forest plant life‐forms (trees, shrubs and herbs) in a large temperate forest region. Location Northeast China. Methods We quantified ecological uniqueness as abundance and incidence‐based local relative contributions to beta diversity (i.e. LCBD indices) in the study region. Multiple beta regression analyses and piecewise structural equation models were used to determine the relative direct and interactive effects of four processes in shaping ecological uniqueness across forest plant life‐forms. Results The southern area of the region exhibited consistently greater LCBD values across plant life‐forms, highlighting its importance for conservation. All four processes jointly affected ecological uniqueness but their relative importance varied across plant life‐forms. Generally, regional climate had the dominant effect on tree LCBD while biotic heterogeneity was the most important process driving shrub and herb LCBDs. Local environmental filtering was less important in driving LCBD of all life‐forms. The significant direct effect of DI was only found in the herb group. Despite its weak direct effect, DI could indirectly shape tree and shrub LCBDs via biotic heterogeneity. Main Conclusions Our study suggests that current patterns of ecological uniqueness (i.e. LCBD) across forest plant life‐forms result from multiple processes, with regional climate filtering and biotic heterogeneity having the strongest effects on uniqueness patterns across all life‐forms. Meanwhile, DI is more critical for shaping ecological uniqueness of herbs than trees or shrubs. We highlight the interactive roles of biotic and abiotic filtering in shaping biologically distinct communities important for biodiversity conservation.