祁连山东部高寒山区林下植被多样性的驱动因素OA

[Objective]This study aimed to investigate how topographic factors,stand structure,and soil nu-trients drive understory vegetation diversity in alpine forest ecosystems,and to determine whether these driving mechanisms exhibit significant stratified differentiation between the shrub and herb layers.[Methods]Based on the natural secondary forests in the eastern Qilian Mountains,a total of 64 plots were established across an elevational gradient of 2 700～3 100 m and across different topographic conditions.Stand structural characteristics,soil physicochemical properties(including pH,soil organic carbon,total ni-trogen,alkali-hydrolyzable nitrogen,available potassium,and soil moisture content),and topographic vari-ables(elevation and slope)were systematically measured.Four diversity indices,namely the Margalef richness index,Simpson diversity index,Shannon-Wiener diversity index,and Pielou evenness index,were calculated.Redundancy analysis(RDA),linear mixed-effects models(LMM),and variance partition-ing analysis(VPA)were employed to comprehensively reveal the driving mechanisms underlying diversity patterns in the shrub and herb layers.[Results]Understory vegetation diversity was generally higher in the herb layer than in the shrub layer,with pronounced differences among valleys.Shrub-layer diversity was highest in Qihan Gully,whereas herb-layer diversity reached its maximum in Tacang Gully.Results from the LMM and VPA indicated that elevation was the dominant factor affecting understory vegetation di-versity,independently explaining 22.74％and 16.31％of the variation in shrub-and herb-layer diversity,re-spectively.Shrub-layer diversity was primarily driven by soil factors,while topographic and soil factors ex-erted relatively independent effects.In addition,the random effect of valley was significant(ICC=24％).In contrast,herb-layer diversity was mainly influenced by the interaction between topography and stand struc-ture,which explained 12.31％of the observed variation.Soil factors made a relatively small contribution,explaining only 4.63％of the variation,and showed no shared explanatory effect with other factor groups.Furthermore,herb-layer diversity exhibited a significant unimodal relationship with slope,reaching its max-imum at approximately 25°,whereas no significant relationship was detected between shrub-layer di-versity and slope.[Conclusion]Understory vegetation diversity in alpine mountainous regions exhibits pro-nounced stratified differentiation.Herb-layer diversity is mainly regulated by cascading effects of topo-graphy through stand structure,and the associated understory light environment.In contrast,shrub-layer diversity is mainly controlled by the combined effects of soil nutrient availability and resource competition under varying topographic conditions.These findings provide a scientific basis for close-to-nature forest management and biodiversity conservation in alpine forest ecosystems.