Relict vegetation on mesic sites

Vegetation is a dynamic system of interacting plant populations. In spite of this dynamism, different vegetation types exhibit a variable amount of inertia in species composition. For this reason, the current vegetation of Central Europe is a heterogeneous mixture of plant communities of different age, depending not only on site conditions, but also on the history of vegetation development. We use the term “relict vegetation” for vegetation with an extraordinarily high proportion of species or species combinations which used to be more abundant in the past and may thus be considered as remnants of their wider past distribution. Although there is an almost infinite number of unique local histories of plant populations and their sites, within which a number of milestones might be identified, only two kinds of vegetation relicts are frequently distinguished in Czech botanical literature: 1) Glacial and Early Holocene relicts, i.e. remnants of plant communities widespread during the last Glacial period or the subsequent period of the Early Holocene but retreated mostly due to the spread of shady forests during the mid-Holocene; and 2) cultural relicts, i.e. vegetation types shaped by human activities which used to be more common in the past but have recently been abandoned. In this study we focus on relict vegetation on mesic sites at lower altitudes in the Czech Republic. Here, natural vegetation is represented mostly by oak-hornbeam and beech forests (Carpinion, Fagion) and semi-natural vegetation mostly consists of nutrient-rich mesic grasslands (Arrhenatherion) and relatively species-poor types of semi-dry grasslands (Bromion erecti). Although mesic lowland and upland sites were predominantly intensively managed in the past, we suggest that in some places ancient vegetation types were preserved both in forest and non-forest habitats. We assume that most relict vegetation types of mesic sites are derived from communities which used to be widespread before the mid-Holocene. Based on palaeoecological evidence, these were open-canopy forests dominated mainly by Betula and Pinus, whose total species composition is unknown but may be approximated using recent analogues from continental regions of Eurasia. Hemiboreal Brachypodio pinnati-Betuletea pendulae forests, distributed from the Southern Urals to southern Siberia, include many central European species which we suggest are characteristic of relict communities of both forest and non-forest vegetation in central European lowlands and uplands. These communities mostly include extensively managed species-rich mesic, dry-mesic and wet-mesic grasslands on base-rich to moderately rich but nutrient-poor to moderately rich soils (Cirsio-Brachypodion, Molinion and mesotrophic variants of Arrhenatherion) and open-canopy mesic to dry-mesic oak forests on base-rich to moderately rich soils. Characteristic species include Betonica officinalis, Brachypodium pinnatum, Potentilla alba, Galium boreale, Viola hirta, Carex montana, Inula salicina, Peucedanum cervaria and Primula veris. Many sites of these communities harbour some rare species with disjunct distribution ranges, which we interpret as another indication of relict origin of this vegetation. Besides hemiboreal forests we discuss several vegetation types whose historical analogues could be ancestors of recent relict communities of mesic sites: continental forest meadows (Carici macrourae-Crepidetalia sibiricae), steppe meadows (Galietalia veri), and also some types of alluvial and fen grasslands. Open-canopy forests of the Southern Urals (Lathyro-Quercion roboris), whose understorey is almost identical to that of hemiboreal Brachypodio-Betuletea forests, represent a hypothetical analogue of mid-Holocene mixed oak forests (Quercetum mixtum) from which the current subcontinental oak forests (Potentillo-Quercetum sensu lato) in Central Europe have been derived. We also provide detailed characteristics of several vegetation types occurring in the Czech Republic which we consider as vegetation relicts. We identified several factors possibly important for their preservation: long history of human influence, which was relatively intensive in the more distant history (and thus could have facilitated the survival of heliophilous communities at the expense of shady forests) and relatively low-intensive in recent history (and thus could have prevented the spread of competitive species or complete destruction by human activities). This vegetation frequently survives at remote and poorly manageable sites, yet with a long history of human influence.