Polar terrestrial ecosystems: ecology, diversity, and biogeography

The Arctic and the Antarctic, surrounding the two poles of the globe, share several features and at the same time have contrasting biogeographical constitutions, which influences fundamental aspects of their terrestrial ecosystems. The polar regions and their extreme environment have deeply fascinated naturalists for centuries. Polish polar research has a long tradition dating back to the nineteenth century with the prominent participation of two Polish scientists, Henryk Arctowski (1871–1958) and Antoni Bolesław Dobrowolski (1872–1954), in the famous international expedition to the Antarctic on the ship Belgica in 1897–1899, as the most symbolic opening event [1]. Within the framework of the polar exploration for over more than a century, but especially during the last decades, Polish botanists have contributed considerably to the general knowledge on biodiversity, taxonomy, biogeography, and ecology of the Arctic and Antarctic flora, especially key groups for these biomes such as lichens (lichenized fungi) and mosses (see [2,3] for some overviews). These long-term studies have resulted in a wealth of data including comprehensive regional accounts (e.g., [4–7]) and key syntheses, becoming benchmark references for global research, as best exemplified by the seminal The illustrated moss flora of Antarctica by R. Ochyra et al., published by Cambridge University Press in 2008 [8]. In 2017, Polish polar research celebrated the following two important anniversaries: the sixtieth anniversary of the Polish Polar Station in Hornsund, Svalbard (Arctic) and the fortieth anniversary of the H. Arctowski Polish Antarctic Station in the King George Island, South Shetland Islands (Antarctica). These two remote outposts are arguably the most significant icons of Polish scientific exploration globally [9]. Hence, as meaningful landmarks in Arctic and Antarctic studies, these anniversaries inspired the present special issue of Acta Societatis Botanicorum Poloniae (ASBP) focused on botanical exploration of harsh, polar terrestrial ecosystems. The current issue is the fourth themed edition of ASBP, which is preceded by the special issues of the journal published in 2012 (vol. 81, issue 4), 2014 (83/4), and 2016 (85/4). It contains 14 articles, which provide a fair overview of botanical research carried out in the polar regions, aiming at better describing and understanding the biodiversity, ecology, and biogeography of these exceptional and fragile terrestrial environments. They also reflect the main aspects of recent Polish research activities in polar plant biology, concentrating on all the major groups of organisms traditionally treated as plants, including vascular plants, mosses, lichens, lichenicolous fungi, and algae. Studies on biodiversity in the polar regions become especially necessary in the context of ongoing dramatic environmental changes induced by the global warming climatic trends, including emergence of new terrestrial habitats due to massive deglaciation. The articles gathered in this special issue cover a wide range of topics on polar plant biology. As a formal classification, they can be assigned mainly into the following two categories: (i) ecology and (ii) taxonomy and phytogeography. However, they are often placed at the interface of biodiversity and related ecological and biogeographical factors, and in some cases also including anthropogenic influence. Seven articles deal with central themes of plant ecology such as succession, the universal process of DOI: 10.5586/asbp.3610