Soil nutrients mediate the indirect effects of shrub canopy removal: How distance from shrubs affects the herbs and grasses community in a shrub‐encroached grassland

Abstract

Understanding community processes is essential to predict community dynamics and succession processes. To explore how shrub canopy removal frequency (hereafter ‘removal frequency’) and distance from shrubs affect herbs and grasses community assembly in a shrub‐encroached grassland, we carried out a 4‐year shrub canopy removal experiment with three removal frequencies (no removal, removal once, and removal twice per year) in a Caragana microphylla shrub‐encroached grassland, and assessed community assembly mechanisms directly beneath shrubs (0 m from shrubs, i.e., in the centre of the shrub) and in shrub interspaces (at least 2 m from shrubs) under each removal frequency treatment using both functional trait‐based and phylogenetic‐based approaches. Removal frequency positively affected standard effect sizes (SESs) of the mean pairwise distance (MPD) for multi‐trait, specific leaf area (SLA) and leaf dry matter content (LDMC), denoted by SES.MPDMulti‐trait, SES.MPDSLA, and SES.MPDLDMC, indirectly via regulating soil nitrogen (N) and soil carbon (C) content, while it negatively affected SES.MPDHeight indirectly via regulating soil available phosphorus (P) content. Distance from shrubs negatively affected SES.MPDHeight indirectly via regulating soil available P content, and negatively affected SES.MPDLDMC indirectly via regulating soil C content. The trait‐based approach was more powerful than the phylogenetic‐based one in explaining the responses of community assembly processes to environmental changes. These findings highlight the importance of shrub canopy removal and distance from shrubs in affecting soil nutrient status and consequently community assembly processes, which provides a new insight into how canopy removal or fertile island effects affect community assembly in the shrub‐encroached grassland regions.