Objective This paper aims to explore the changes and associations of multidimensional diversity of forest plants in Luo Mountain, Ningxia of northwestern China, and reveal the dominant drivers of community construction.

Method Five typical forest communities were studied, including Picea crassifolia pure forest, Picea crassifolia × Pinus tabuliformis mixed forest, Pinus tabuliformis pure forest, Pinus tabuliformis × Populus davidiana mixed forest, and Populus davidiana pure forest. This study employed multidimensional indices of biodiversity combined with functional traits and environmental factors, and systematically analyzed the correlations among multidimensional diversity and community construction processes.

Result (1) Species diversity (Simpson index, Margalef richness index) and functional diversity of Picea crassifolia pure forest were significantly lower than those of mixed forests (P < 0.05), while there was no significant difference in phylogenetic diversity among different forest types (P > 0.05). (2) Species diversity index was significantly positively correlated with functional diversity index and phylogenetic diversity index, respectively (P < 0.05), while there was no correlation between functional and phylogenetic diversity (P > 0.05). (3) Picea crassifolia and Pinus tabuliformis pure forest exhibited divergent phylogenetic and functional trait structure, indicating community construction dominated by competitive exclusion. Picea crassifolia × Pinus tabuliformis mixed forest showed local aggregation with overall divergence in phylogenetic structure, and Pinus tabuliformis × Populus davidiana mixed forest showed local aggregation with overall divergence in functional trait structure, which both suggested community construction co-driven by competitive exclusion and environmental filtering. Populus davidiana pure forest displayed aggregated phylogenetic and functional trait structure, indicating community construction dominated by environmental filtering. (4) The phylogenetic signals of seven leaf functional traits were all less than 1, indicating inconsistency between functional traits and phylogenetic structure and their variations were mainly driven by environmental heterogeneity. Altitude, soil pH, organic carbon, and total nitrogen were identified as the key environmental factors affecting functional trait differentiation.

Conclusion Species diversity is positively correlated with functional diversity and phylogenetic diversity, while functional traits show a decoupled relationship with phylogeny in Luo Mountain, Ningxia of northwestern China. Community construction process is primarily governed by niche theory, with dominant drivers varying among different forest types. Specifically, pure coniferous forest is dominated by competitive exclusion, pure broadleaved forest is dominated by environmental filtering, and mixed forests are co-driven by these two processes.