Invasive exotic species

The spread of invasive exotic species in the environment represents one of the major causes of damage to biodiversity. Invasive species can also have considerable economic and health impacts.

At the start of 2015, the database produced by the Belgium forum of invasive species included 87 species found in Belgium, of which 43 are on the black list (species having a high environmental impact). 49 species (of which 26 are on the black list) included in this database have been catalogued in the Brussels Region over the period 2011-2014. These are essentially vascular plants. Of these species, 6 were observed for the first time in regional territory between 2011 and 2014: 4 vascular plants (of which 3 are on the black list), 1 bird and 1 fish. 12 invasive species - essentially plants - observed in the Brussels Region between 1900 and 2006 were not categorised over the period 2011-2014. However, this does not mean that they are no longer present, bearing in mind the absence of the systematic monitoring programme.

The problem of invasive exotic species

For centuries, humans have introduced animal and plant species, either deliberately or accidentally, outside of their natural distributional range. Some of these species adapt to the local conditions, successfully reproduce and disperse far and wide by colonising semi-natural habitats in particular. These species are increasingly plentiful due to growing economic globalisation and the explosion of tourism.

The spread of some of these exotic species in our environment is likely to lead to the extinction of indigenous species and have a considerable negative impact on the functioning of ecosystems (due to competition with local species for food or reproduction sites, invasive behaviour in the absence or reduced presence of natural enemies, excessive predation, invasions of water bodies, etc.).  They can also have considerable economic impacts (crop damage, restriction of activities including navigation or water-based recreation, the regulating or restorative measures of biodiversity, etc.) and health impacts (infectious diseases, allergies, skin burns, etc.).

Consequently, these exotic species - referred to as invasive - are the subject of studies which are designed to observe their presence and their progression, to identify their ecology and possible impacts, as well as identify the management measures to be implemented in order to limit these impacts.

Invasive exotic species in the Brussels Region

The Belgium forum for invasive species collects information and updates a database of the invasive species threatening local diversity ("Harmonia"). At the start of 2015, this included 101 species (vs 90 in 2009) of which 43 are on the black list (high environmental impact), 38 are on the watch list (moderate environmental impact) and 14 on the alert list (species with moderate or high impact which are found in neighbouring countries). The 6 remaining species are considered as having a very limited impact.

49 species (of which 26 are on the black list) listed in the Harmonia database were itemised in the Brussels Region over the period 2011-2014; almost three-quarters of them are vascular plants. However, it is likely that the number of invasive species which are actually present is higher, insofar as there is no systematic monitoring programme. In particular, some invasive exotic species whose presence in the Brussels Region was itemised before 2011 are probably still present.

Of these 49 species, 6 were observed for the first time within regional territory between 2011 and 2014: 4 vascular plants (of which 3 are on the black list), 1 bird and 1 fish.  The 4 plant species have only been spotted at one or two sites to date.

The alert list drawn up for the Brussels Region includes 46 species.  It is made up of invasive species observed at the regional level over the period 1900-2006, but which have not been spotted since (12 species), as well as invasive species observed in the rest of the country - sometimes close to the regional boundary - and in neighbouring countries (alert list from the Harmonia database), but not in the Brussels Region.

The case of the rose-ringed parakeet

Having escaped or been set free, 3 species of green parakeets have perfectly adapted and nested in large numbers in the Brussels Region. The exponential development of these parakeets from the 1990s onwards meant that they became the focus of special monitoring. According to a study (from 2008) conducted at the request of Brussels Environment by Natagora on the proven and potential impacts of rose-ringed parakeets (Psittacula krameri), the disturbances at the Brussels Region level mainly occur in bird houses (noise, droppings, occasional damage to trees). The major concern is that these species nesting in cavities are in extreme competition with local cavernicolous species of birds and bats. Although such an impact has not yet been proven, the question remains, particularly in the scenario where there is a shortage of cavity trees.

For several years, experts have observed a considerable expansion in parakeet populations outside of Brussels, as shown in the maps below. To the extent that parakeets are fruit eaters, significant damage can be observed in areas where orchards constitute important economic activity, in particular in the Pajottenland.

Observations of rose-ringed parakeets (Psittacula krameri) in and around the Brussels Region during the periods 2007-2010 and 2011-2014 (based on observations submitted to the observations.be website)
Source: www.observations.be

Actions taken by the Brussels Region

There is no comprehensive action plan at the present time for controlling invasive exotic species at the Regional level.  Nonetheless, numerous initiatives have already been carried out, including:

• information and awareness-raising among the broad public of the problems caused by certain invasive species and the actions they can take to minimise them (info-sheets, brochures, websites, etc.);
• information and awareness-raising among professionals in the horticultural sector intended to reduce the cultivation and sale of invasive plants and encourage the use of alternative indigenous species instead (via the co-financing of the national LIFE+ project "AlterIAS");
• dissemination of information (technical sheets) and training of ground staff in the management of certain invasive plants;
• management on the ground of particularly problematic invasive species such as the black cherry (Prunus serotina), the Japanese knotweed (Fallopia japonica) or even the giant hogweed (Heracleum mantegazzianum);
• financing, via public procurement contracts or grants, of projects designed to study the potential impact of certain exotic species found in the Brussels Region.

Given the trans-regional aspect of the problem, Brussels Environment also participates in working groups, expert advice and study steering committees which are organised at the supra-regional or international level. There are also legislative tools, particularly in the context of the ordinance of 1 March 2012 on nature conservation. For example, this prohibits the planting of non-indigenous species in natural reserves and subjects the deliberate introduction of non-indigenous animal or plant species in the natural environment to authorisation. Article 78 of this ordinance authorises the Government to take eradication measures with regards to certain invasive species, if deemed necessary. It should also be noted that the draft nature plan, currently in the process of being adopted, includes a measure intended to optimise the management of invasive exotic species.