Occurrence of neophytes in agrophytocoenoses - field survey in the Czech Republic.
Neophytes belong to a group of non-native plants, which were introduced by man either intentionally or unintentionally in different ways. The discovery of America is a historical milestone for non-native plant research. Most scientists use the term neophyte for species introduced after the year 1500. Neophytes became progressively more numerous in arable fields and their proportion significantly increased during the second half of the 20th century. The aim of this study was to assess the occurrence of neophytes in arable fields in the Czech Republic in terms of applied management systems, crops, and environmental site conditions at different altitudes. In the years 2006 to 2008, a phytocoenological survey was conducted on selected farms across the Czech Republic under various climate and soil conditions in spring and winter cereals and in wide-row crops. Totally, 172 weed species were found. Among these species, 8% were considered as neophytes (13 species). In respect of their stage of invasiveness, 6 neophytes were considered as invasive, 6 species as naturalized and 1 species was considered as casual. Frequencies of neophyte species we found ranged between 0.3-31% from all relevés. Environmental site conditions associated with altitude were the most important factors correlated with the occurrence of neophytes. The incidence of neophytes is primarily concentrated at lower altitudes and is mainly associated with stands of spring wide-row crops, especially root crops and vegetables. A higher proportion of neophytes was found in organic farming.