| Description |
We present the third edition of the complete catalogue of the alien flora of the Czech Republic which follows the 2002 and 2012 editions. It has been updated by incorporating new data collected over the last decade and reassessing the current status of taxa based on improved taxonomic and ecological knowledge. All changes in taxon listing from the 2012 version are documented and explained in an appendix. Based on comprehensive data sources, including the recently developed Pladias database of the Czech flora and vegetation and the Archaeobotanical Database of the Czech Republic, we list 1576 taxa alien to this country, with information on their taxonomic position, life form, geographic origin, residence time status (archaeophyte or neophyte), invasion status (casual, naturalized or invasive), date of the first and last field record, grid-cell occupancy, pathway of introduction into the country, habitat affiliation and impact assessment. This edition includes 122 more taxa than the 2012 edition; 157 taxa were added and 35 were removed; 17 taxa were reclassified as native, eight were removed due to lack of evidence, records of six taxa were assessed as doubtful, and four are not taxonomically justified. The alien flora is recruited from 630 genera and 122 families and comprises 385 archaeophytes and 1191 neophytes; most taxa are casual (1084, i.e. 68.8% of the total number), 417 taxa are naturalized (26.4%), and 75 are invasive (4.8%). The proportion of invasive taxa is almost equal for archaeophytes and neophytes (4.7 and 4.8%, respectively), casual taxa are over-represented among neophytes, and naturalized taxa among archaeophytes. The contribution of alien taxa to the Czech flora is 37.8% if all aliens are considered or 16.2% if all naturalized taxa (including invasives), which are a permanent part of the flora, are included. For all groups of invasion status, the numbers of taxa are increasing over time with no sign of deceleration. Most alien plants originate from the Mediterranean region (618 taxa, i.e. 31.5%), other parts of Europe (380 taxa, 19.4%), other parts of Asia (290 taxa, 14.1%) and North America (262, 13.4%). The highest number of invasive taxa (27, corresponding to 27.6% of all invasive archaeophytes and neophytes) are from North America. Occupancy of grid cells of 10 × 6 arc minutes significantly increases with invasion status and residence time. Invasive taxa are present in more grid cells than naturalized and casual, and archaeophytes occupy on average more grid cells than neophytes in each invasion status category. Maps based on the cumulative record of alien species occurrence over the past 50 years, expressed as the proportion of the entire flora, show that alien species are relatively more prevalent in lowlands and large urban agglomerations. In a European comparison, the Czech Republic is currently a moderately invaded country, but slightly richer in naturalized species than the European average.
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