[Invasive-species] criteria for a list of invasive species

[Roger Cammaerts]

Dear all,

The critera you suggest for the building up of a list of invasive exotic species in Belgium sound fair, but I want to add a remark.

For animals, the date criterium for naturalized species (category D) could be taken shorter than for plants (1500). For instance, the Amphipod Gammarus roeseli is considered to be a naturalized species, although it was only encountered for the first time in 1931 in Belgium, this is not yet a century .But for the Amphipod specialists, it is established “since long” in our country and it seems to be in balance with its environment. Moreover, it is apparently restricted to some portions of turbid rivers and do not appear to be invasive.

May I add that, according to a decree of the Flemish Government of 31 April 1993, animals present for more than 50 years in Flanders are not more considered to be exotic to the fauna. As a consequence to this arbitrary decree, Orconectes limosus, seen for the first time in Belgium in 1962, might soon receive the status of  naturalized crayfish. It is possibly is in balance with its environment (large turbid rivers as well as smaller waters of good quality) and we may suspect that it has taken the place of our native Astacus astacus, long ago ruled out of these rivers by pollution and pleague. 

What I want to say is that we never should lose sight  that all classifications are somewhat arbitrary.  
  
Dr Roger Cammaerts, 
Laboratoire de Systématique et d'Ecologie Animales,
Université Libre de Bruxelles,
CP 160/13
av. F.D. Roosevelt 50
B-1050 Bruxelles
Belgique