Which species are alien?
Alien species are those, brought in from outside, which are not naturally distributed in Bulgaria. Their arrival is the result of human activity – transport, tourism, trade, agriculture, gardening, afforestation. Sometimes introduction happens when the natural barriers across countries and continents are breached – through bodies of water, by birds and animals, etc.
Most invasive alien plant species (IAS) possess powerful reproduction and survival mechanisms. They do not have particular environmental requirements or natural pests. IAS plants are easily naturalised and spread without the aid of humans.
Some of the most widespread and dangerous invasive alien plant species in Europe are tree of heaven, common ragweed, black locust, indigo bush, himalayan balsam, japanese knotweed, boxelder; annual fleabane, canadian fleabane and others.