Invasive plant species

Flora of Latvia or the present plant species composition has developed during the last 10 000 years. Since the first foreign species were introduced several centuries have passed. Separate foreign plant species have been able to overcome the local competition and have become a part of natural ecosystems or naturalised without suppressing the local species. These species are called arheophytes. For example, in the 16th century in Latvia was brought in a medical plant - Acorus calamus that was planted in the ponds of manors. Nowadays Acorus calamus is widespread both near ponds, lakes and rivers. The plant has found its ecological niche and completely stabilised in natural ecosystems.

Several centuries ago with human help in Latvia have appeared also other species, like Viola arvensis, Solanum nigrum, Papaver rhoeas and Urtica urens. Time of arrival of many plant species in Latvia can be determined only approximately. More precise information about several cultural plants and weeds that follow them is obtained from archaeological excavations. Both species that appeared in a natural way and arheophytes are assigned to natural or aborigine (autohtone) flora.

Species that appeared in Latvia with human help and that are called neophytes are considered as foreign (allohtone) flora. To this group belong species, like Populus alba, Solidago canadensis and Artemisia absinthium. With every year increase the density of foreign species in Latvian plant species composition. Studies of specialists of Institute of Biology, Laboratory of Botany show that already 33 % from Pteridophyta and Spermatophyta flora are foreign species (Gavrilova, sulcs 1999). To these species belong escapers from gardens as well as invasive or adventive species and foreign tree species that are grown in forest cultures. Most of foreign species can not compete with local species, therefore in natural ecosystems occur in relatively small areas or their life span is short.