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

Prepared by Kamila Reczyńska & Krzysztof Świerkosz

Early spring aspect of one of our rocky grassland replot from the Alysso-Festucion pallentis Moravec in Holub et al. 1967 alliance, on serpentinites in the Góra Radunia nature reserve (Sudetes Foreland, Poland, 20.04.2009). Photo credit: Krzysztof Świerkosz

Recent years have brought dynamic changes in the vegetation worldwide arising from the destruction or transformation of ecosystems by humans, climate change, nitrogen pollution and the introduction of invasive species. These changes have been intensively studied, especially in forest, grassland, and alpine communities. However, the very rare research subject is rock plant communities, which seem to be most exposed to climate. This particular type of plant community develops on ledges and in crevices of rocks – places practically devoid of soil. In summer, they are exposed to the scorching rays of the sun and drought, punctuated by heavy rainfall. During Central European winter, they are affected by frosty winds, and freezing water which burst rock crevices. In turn, in shaded places, they suffer from constant lack of sunlight, and accumulation of thick layers of organic matter created by leaves falling from neighbouring trees, hindering young plants’ growth. Therefore, we expected that in the course of our research we would detect much more significant changes in rock plant communities than those found in forests or alpine grasslands. For this purpose, we compared plant species compositions within 214 plots located in the Sudetes (SW Poland) by recording plant species based on specific standard scale. We conducted at least two surveys at each site. The oldest of these censuses date back to 1989, and the latest to 2022. The period between surveys ranged from 6 to 31 years (average 14.2 years). Then, using statistical methods, we compared changes that occurred within individual plots in species composition itself but also in habitat conditions and functional plant traits under large-scale (climate warming, nitrogen deposition) and local-scale factors (light availability, geological substrate, initial site conditions). The results turned out to be surprising. In the entire set of 258 species, only 11 showed a slight increase in their share between the initial and final survey, and these were species from different ecological groups (both light-demanding and shade-tolerant). We also detected some compositional differences between the plots from the first and second research periods, but they were statistically insignificant. Nevertheless, we were still curious about which group of factors (large- or local-scale) influences our communities in relation to the shifts in habitat conditions and functional plant traits. Large-scale factors were responsible for changes in habitat conditions only in a few analysed cases whereas the impact of changes in light availability and the initial site conditions turned out to be much more important. We observed these relationships regularly, for various types of rocks. We obtained similar results by analysing the functional characteristics of communities, expressed by changes in basic leaf or seed characteristics. Our study, therefore, suggests that in the analysed period of time, large-scale environmental factors, such as global warming and nitrogen pollution, are still of marginal importance. This means that rock communities, despite potentially high exposure to drought and high temperatures, have been surprisingly resistant to them so far.

An exemplary replot in shaded communities is the Hypno-Polypodietum Jurko et Peciar 1963 association in the Opawskie Mountains (Western Sudetes, Poland, 01.09.2010). Photo credit: Krzysztof Świerkosz

This is a plain language summary of the paper of Reczyńska K. & Świerkosz K. published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.13263)