Solid as a rock: The main drivers of changes in natural, rocky plant communities

Abstract

QuestionChanges caused by climate warming and nitrogen pollution are observed in forest, grassland and alpine ecosystems worldwide. However, still little is known about the impact of these globally influencing factors on natural rocky plant communities. Has species composition of natural rocky communities changed over time? What is the role of large‐scale and fine‐scale environmental factors in shaping the compositional, functional and habitat patterns in studied plant communities over time?LocationSudetes Mountains, southwestern Poland.MethodsWe used 214 pairs of replots (collected between 1989 and 2022) of rocky plant communities, with a mean timespan of 14.2 years. The changes in species composition, environmental conditions and functional traits were analysed using ordination techniques and generalised additive models (GAMs) and with reference to large‐scale factors (mean maximum temperatures, actual evapotranspiration, N deposition) and fine‐scale factors (light availability, bedrock type, initial site conditions) for each locality.ResultsSpecies composition of the studied communities has not changed significantly over time. Only for 11 out of 258 species, statistically significant increases (from 2% to 8%) in their proportion were recorded. The changes in environmental conditions were significantly influenced mainly by fine‐scale factors such as changes in light availability and baseline site conditions. Plots that were initially less thermophilic or nitrophilic showed stronger signals of thermophilisation and eutrophication in the resurvey. The influence of large‐scale factors was considerably less pronounced. Similarly, the key role in explaining changes in plant traits for the data set under study falls to local factors, particularly changes in light availability.ConclusionsOur study confirms the validity of considering both large‐ and fine‐scale factors as well as initial site conditions in research on long‐term changes in plant communities. Rocky plant communities respond to global changes in a different way than other types of phytocoenose, showing high stability of species composition and functional traits over time.