Popular Science: Amazing discoveries of Pliocene flora
The Earth's climate has changed significantly during the Pliocene (the epoch in the geologic timescale that extends from 5.33 to 2.58 million years BP). The first phase, which followed the Miocene period, was about 3 °C warmer than today and was characterized by the occurrence of exotic plant species in the areas of today's temperate zone. Some of them persisted as relicts, but with later cooling and subsequent Pleistocene glaciation there were significant changes in the structure of the existing flora.
The discovery of the Pliocene flora of Frankfurt am Main presented the key vegetation of this period and was ranked among the one of the most important findings in Europe. After Mädler’s monograph, published in the first half of the 20th century, the Frankfurt flora has never been revised. Unfortunately, most of the material of Pliocene flora collected since 1885 at the Senckenberg Research Institute and Natural History Museum in Frankfurt as a unique “glass herbarium“ was destroyed during World War II.
In current research, scientists set out to revise the so-called "Klärbecken Flora", named after the site southwest of Frankfurt, while assessing the unpublished materials recovered after World War II. The other goals were focused on the description of the paleoenvironment and paleoclimate conditions of this period.
It was necessary to go through all the materials connected with the Pliocene flora. While studying the collections in Frankfurt am Main, Professor Zlatko Kvaček noticed a stray sheet of paper from an unknown author from the late 1930s. It was a list of material sent to the Swedish Museum of Natural History in Stockholm containing plant names with outdated taxonomy. It turned out that Pliocene flora are likely to be found in more institutions - not only in Frankfurt, but also in Stockholm and London.
The authors used two methods to assess the climate and environmental conditions. Firstly, the CLAMP method (Climate Leaf Analysis Multivariate Program), whose main essence is to compare the morphological or architectural leaf variables of dicotyledons.
This method examines 31 different leaf character states using data from 144 recent sites and 173 existing biotopes. It is thus one of the best objective methods based on numerical data. Another method was the semi-quantitative IPR (Integrated Plant Record) method, which was developed as a proxy (indirect data to reconstruct past climatic conditions) to assess the classification of zonal vegetation and was recently tested by one of the authors using contemporary European and Caucasian plants.
The final revised and extended flora list comprises 16 gymnosperm species in 15 genera and 73 angiosperm species in 40 genera. Compared to earlier records, it now contains 7 new species and some new combinations of taxa previously described by Mädler. The resulting flora list is characterized in particular by the high diversity of conifers, Fagaceae and Rosaceae. The findings indicate cool temperate climatic conditions (comparable to today's southern Switzerland) during the Pliocene era. A large number of taxa are currently absent in Western Eurasia and North America.
The main results show a strong biogeographical link of the Pliocene flora of Frankfurt am Main with East Asia, surprisingly high levels of speciation (the occurrence of Pliocene endemisms = the ecological state of a species being unique to a defined geographic location) and that the European flora was more diverse in woody species before the onset of the Pleistocene glaciation than today.
Let's have a look into the amazing world of the Pliocene flora, which is now presented by scientists from the Czech Republic and Sweden. You will learn not only about the plant species growing in this historic era, but also about the local climate and environment. This will undoubtedly enrich knowledge, and not only for specialized botanists.
Kvaček, Z., Teodoridis, V., Denk, T. (2019): The Pliocene flora of Frankfurt am Main, Germany: taxonomy, palaeoenvironments and biogeographic affinities. Palaeobiodiversity and Palaeoenvironments. s. 1–57. https://doi.org/10.1007/s12549-019-00391-6.