Holocene fire dynamics mitigate the negative effect of catchment acidification on mountain submerged macrophytes (Isoëtes) in Central Europe
Abstract
Modern populations of submerged macrophytes, Isoëtes, are classified as a critically endangered species after undergoing large declines in Central Europe. Recent studies have attributed Isoëtes decline to modern human impact, namely eutrophication, acidification or alkalization induced by land-use changes.
However, anthropogenically driven environmental changes may not be an exclusive cause of Isoëtes decline. Paleoecological reconstructions illustrate a wide distribution of Isoëtes populations in the past, especially during the Early and Middle Holocene when human impact was less intense.
Here, we aim to investigate how local environmental factors may have impacted the distribution and abundance of Isoëtes populations during the Holocene. To complete our research aim, we used a multi-proxy approach utilizing plant macrofossils, macrocharcoals, pollen, diatoms and chironomids from four lakes (Prášilské jezero, Plešné jezero, Černé jezero, Rachelsee) located within the Bohemian/Bavarian Forest mountain range in Central Europe.
Our results show regional, synchronous patterns, with Isoëtes colonization beginning between 10 300 - 9 300 cal yr BP, and substantially declining around 6 500 cal yr BP. Results from Prášilské jezero imply that Isoëtesdynamic was mainly driven by processes connected with a change in vegetation structure and composition and fire regime around 6500 cal yr BP.
Specifically, Fagus expansion and peatland extension coincide with decreasing fire activity, which changed soil chemistry in the lake catchment, and through surface water runoff, altered both the physical and chemical properties of lake water. This is reflected by a shift in diatom assemblages towards more acidophilous species and a distinctive drop in chironomid abundance.
These environmental changes likely lead to an attenuation in the light availability, which subsequently resulted in the decline in Isoëtes abundance. Our study demonstrate the importance of vegetation development and fire dynamics in determining the abundance and distribution of critically endangered Isoëtes populations.
These results have major implications for management and highlight the importance of long-term records in policy making.