Plant invasions in the Czech Republic: current state, introduction dynamics, invasive species and invaded habitats.

The Czech Republic has a strong tradition of research on synanthropic and alien plants, both historically and recently, which results in a good knowledge of alien flora and invasion patterns. In this paper the current situation of plant invasions in the country is reviewed from the viewpoint of the composition of the country’s alien flora (based on a recently published checklist of alien taxa) and that of the level of habitat invasions, expressed as the proportion of alien species among all species recorded, and large-scale patterns of invasions in landscapes. At present there are 1454 alien taxa recorded in the national flora, consisting of 350 archaeophytes, introduced since the beginning of Neolithic agriculture until the end of the Medieval Period, and 1104 neophytes, introduced in the Modern Period. In the last two centuries there was a steady increase in the number of alien taxa without a decelerating trend. Arrivals of neophytes from the Mediterranean region and extra-Mediterranean Europe proceeded at the same speed until ca the 1870s; thereafter the Mediterranean region started to be the main donor of the country’s alien flora. Most species native to more distant areas such as extra-Mediterranean Asia and North America were arriving later. Of the total number of alien taxa, 985 (67.7%) are classified as casual, 408 (28.1%) as naturalized but non-invasive, and 61 (4.2%) as invasive. Alien taxa contribute 33.3% to the total plant diversity ever recorded in the country, or 14.6% to the permanently present flora (excluding extinct natives and including only naturalized alien taxa). These figures are within the range reported from other European countries. Currently there are 11 archaeophytes and 50 neophytes with invasive populations in the Czech Republic. Factsheets of the invasive neophytes are provided with information on their invasion history, ecology, habitat affinities and impact, and the map of current distribution. The highest invasive species densities (illustrated by a map) as well as the highest levels of invasion in plant communities are found in cities and villages and their surroundings, floodplains of large rivers, disturbed regions in the north, and agricultural landscapes and forestry plantations in warm lowlands, especially in southern Moravia, and central and eastern Bohemia. The level of invasion in the country decreases with altitude, with neophytes responding to this factor more strongly than archaeophytes. A new quantification of the level of invasion for all phytosociological alliances of the Czech Republic is presented. The habitats and vegetation types harbouring the highest proportions of alien species in the Czech Republic are generally either those with a high level of disturbance or with fluctuating input of resources, especially nutrients, in some cases also water or light. Habitats with limited fluctuation of resource availability such as dry, wet and saline grasslands, base-rich fens, and broad-leaved deciduous woodlands appear to be rather resistant to invasion. Future spread of alien species will mainly depend on changing land use and climate.