Abstract Context The increase in surface dominated by woody species and the consequent reduction of grassland areas is globally reported phenomenon. This ecological process, known as woody plant encroachment (WPE), is a major driver of landscape change, reshaping spatial patterns and ecological functioning. WPE has been shown to affect various ecosystem variables, including plant diversity. Although taxonomic diversity (TD) has been the focus of most studies, often with inconsistent findings, much less is known about how functional and phylogenetic dimensions of diversity respond to this process. Objectives This study addressed four main objectives: (i) to analyse changes in phylogenetic plant diversity along the WPE gradient; (ii) to explore the relationship between different facets of diversity; (iii) to analyse the degree of decoupling between phylogenetic diversity (PD) and functional diversity (FD) at different levels of encroachment; and (iv) to characterise the patterns of diversity components in relation to woody cover. Methods The research was conducted at four sites in the north of the Iberian Peninsula, where plots were established along a gradient of woody plant cover. Four WPE levels were considered, with a total of 36 replicate plots per level across the study area. In each plot, several indices were calculated to quantify TD, FD, and PD. Results Phylogenetic plant diversity showed a gradual increase with higher cover of encroaching shrubs. Phylogenetic overdispersion was observed in shrubland communities, mainly due to the presence of older lineages such as pteridophytes and gymnosperms. When the analysis was restricted to angiosperms, phylogenetic clustering appeared at lower levels of woody cover, indicating a stronger influence of environmental filters. Regarding the relationships among diversity dimensions, a negative relationship was observed between TD and the other components, FD and PD, highlighting ecological redundancy. In contrast, FD and PD maintained a positive relationship, reflecting trait conservatism across lineages, although this relationship weakened when only angiosperms were considered. The direction of PD–FD decoupling varied depending on the level of woody encroachment and the taxonomic scope analysed: shrubland communities exhibited PD-driven decoupling, likely linked to the influence of non-angiosperm lineages, whereas grassland communities showed FD-driven decoupling, reflecting adaptive divergence among closely related taxa. Both functional and phylogenetic diversity tended to increase along the gradient of encroaching species cover, whereas taxonomic diversity peaked at intermediate covers (5–30%) before declining under higher shrub cover. Conclusions The findings of this study highlight that the different facets of plant diversity do not respond uniformly to increasing shrub encroachment. This reinforces the need for a multifaceted approach to better understand the complexity of the shrub encroachment process.
Sánchez-Carmona et al. (Sun,) studied this question.