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.


Look through the gallery with images of invasive alien plants in Bulgaria


IAS plants establish themselves quickly and take over meadows, pastures and forests. They extract the nutrients and water from the soil and influence the light regime, thus suppressing the development of native plants and leading to their decline and extinction.

Apart from causing irreversible changes to wild nature, IAS plants cause serious economic damage and threaten the health of people, specifically causing:

  • Loss of agricultural produce and ever larger costs for weed control, due to the spread of ragweed, amaranth, Johnson grass, thorn apple, tall fleabane.
  • Reduction of the area of arable land, pastures and meadows, because of the spread of desert false indigo, false-acacia, ailanthus.
  • Destruction of infrastructure – ailanthus, desert false indigo and bohemian knotweed have powerful root systems with many offshoots. The seeds of numerous species disseminate and grow on buildings, churches and monasteries, causing the destruction of cultural monuments, canals and fortification walls.

Some IAS plants like ragweed and giant hogweed cause allergies, asthma and skin diseases (dermatitis).

EU and Bulgaria Policy

The European Union has a specific policy for prevention and management of the introduction and spread of invasive alien species. The main part of it is the EU Regulation 1143/2014 on Invasive Alien Species. The Regulation is binding on Bulgaria and all other Member States. The core of Regulation 1143/2014 is the list of Invasive Alien Species of Union concern (the Union list). The species included on the Union list are subject to restrictions and measures set out in the Regulation. All Member States are required to take concerted actions on them. The first Union list was adopted in 2016. In 2017 and 2019, it was updated. Proposals for the inclusion of new species are regularly considered.

Bulgaria as a Member State of EU also implements the Regulation 1143/2014 on Invasive Alien Species and is developing its national legislative framework and policy against IAS.

Useful Publications on IA Plants Species

  • EPPO Lists of Invasive Alien Plants
    The European and Mediterranean Plant Protection Organization (EPPO) Panel on Invasive Alien Plants is created in 2002 . It has the task to identify invasive alien plant species, which may present a risk to the EPPO region, and to propose management options.


  • A Field Guide to Invasive Alien Species in European Forests
    Published by The Slovenian Forestry Institute. It is developed within the framework of the project Awareness Raising, Training and Measures on Invasive alien Species in forests (LIFE ARTEMIS), which is funded by the European Commission in the framework of the LIFE financial mechanism, the Ministry of the Environment and Spatial Planning of the Republic of Slovenia, the City of Ljubljana and the Slovenian Research Agency.
    It is a useful tool for recognizing and limiting the alien species of trees, shrubs, climbing and herbaceous plants, fungi, bacteria, insects, birds and mammals in the forests. The Guide was first prepared in Slovenian, The English version has been adapted for the international community and many of the species  have been specially added.


  • Invasive Alien Species of Vascular Plants in Bulgaria
    The book is published in 2012 by the Institute of Biodiversity and Ecosystem Research of the Bulgarian Academy of Sciences under a project funded by the Scientific Research Fund. It contains useful information on terminology, historical data and other concerning IA plants.  Sixty (60) IA plant species are presented by numerous pictures and information on: 1) morphological description; 2) biology and ecology; 3) origin and distribution; 4) management options and 5) references.

Presentations on IA Plants Species

  • Nine species from the List of invasive alien species (IAS) of Union concern that are found in Bulgaria: Ailanthus altissima, Asclepias syriaca, Elodea nuttallii, Heracleum mantegazzianum, Heracleum sosnowskyi, Humulus scandens, Impatiens glandulifera, Lagarosiphon major, Pennisetum setaceum.



  • ID sheet with photos for Giant Hogweed, created as part of the RAPID LIFE project, UK


  • Aquatic invasive alien plant species – 36 IA plants are on the Union List of Regulation 1143/2014. 12 of them are aquatic. Two of them entered in Bulgaria: Elodea nuttallii and Lagarosiphon major.

Measures for Control and Limiting Invasion

We must limit the spread of IAS plants, by applying specialised measures, in accordance with the biological and ecological characteristics of each species!

Pursuant to Regulation 1143/2014, Member States are required to take the following measures with regard to IAS affecting the EU: prevention of entry; early detection and rapid eradication of new IAS and control of already widespread IAS. Control measures should be proportionate to the environmental impact and appropriate to local conditions. They aim to eliminate, control the population or limit the spread of the invasive alien species.

There are a few main methods, which show some success in the fight against IA plants: mechanical, ecological, chemical, and biological. It is best to apply a combination of measures, according to the specific conditions and with the active participation of all interested parties.

Improper eradication of IAS trees and shrubs just exacerbates the problem. When they are cut down or burned IAS plants form an abundance of root offshoots, leading to even more overgrowth. There are dormant seeds in the soil and the destruction of mature shrubs and trees illuminates the ground, stimulating the formation of a large number of new plants.

Herbicide treatment can be successful, however the type and quantity must be precisely determined by an expert, in order to avoid soil and water contamination and the destruction of native plants and animals.

A consistent and tenacious fight until complete eradication of the treated groups must be performed in the course of several years. Each remaining stalk gives an opportunity for the root system to recover and create new offshoots.

The most certain way to protect against IAS is to not allow their entry in the first place and to react immediately, upon the first appearance of new plants. Limiting distribution is the main approach toward fighting invasive alien plants. This can happen only with the support of local communities, living in close proximity to the protected areas and Natura 2000 habitats and everyone with vested interest and responsibilities, connected to them. See information and pictures on selected methods for IAS eradication and control.

Within the framework of the project, we apply methods for eliminating and limiting the spread of three of the most aggressive invasive tree and shrub species in Bulgaria  ailanthus, false acacia and desert false indigo. They are included in the list of the most dangerous invasive, alien species, threatening Europe’s biodiversity.

Ailanthus, Tree of Heaven
(Ailanthus altissima)

False Acacia, Black locust
(Robinia pseudoacacia)

Desert False Indigo
(Amorpha fruticosa)