What do we know about the trajectories of local plant community change? A systematic review of resurvey studies

Understanding how plant communities change over time is crucial for effective conservation and biodiversity policy. Here, we conducted a comprehensive literature review of studies on local-scale plant community change using re-surveyed plots. We focus on reported changes in species richness and diversity, by applying chi-squared tests and duration-based generalized linear models to disentangle regional and habitat-specific variations in these changes and identify the primary drivers associated with them. Relevant studies were extracted from Web of Science and Scopus. We applied three inclusion criteria for studies: (i) plots of plant communities, (ii) a minimum of two temporally separate assessments of plant communities, and (iii) inclusion of diversity analyses. Studies meeting all criteria were reviewed. Review papers and meta -analyses were excluded. In total, 812 studies were reviewed. Most studies were from Europe (54 %) and North America (24 %); 41 % of studies focused on forests, 31 % on grasslands, and the remaining on diverse habitats. Ongoing land-use and climate change emerged as the most frequently studied drivers. Increases in species richness (52 %) and diversity/evenness (49 %) were commonly reported, although trends varied by habitat and driver. Habitat-specialist richness was reported separately in only one-third of studies; among study entries reporting a directional change, 73 % reported declines. Longer-duration studies showed more negative outcomes. Surprisingly, there was no detectable difference in biodiversity trends between plots inside and outside protected areas, though this may partly reflect variation in protection status, the timing of area designation relative to first surveys, and the compensatory role of alien species in unprotected sites. Our review reveals considerable context-specific variation in reported local plant diversity trends. These findings underscore the importance of considering regional and habitat-specific contexts, as well as different environmental drivers. Caution is needed when inferring global trajectories from local-scale patterns, particularly given the strong geographic bias toward temperate regions. Addressing geographic and habitat gaps, especially in tropical and underrepresented regions, will be key to improving our understanding of global plant biodiversity dynamics and informing future conservation policies, as current evidence remains strongly biased toward Europe and North America.