Speaking at a biodiversity seminar yesterday, Dokrak Marod of Kasetsart University said although Thai biologists and ecologists have been concerned about alien species for almost a decade, nobody truly understands their nature or the affect on the environment in Thailand.

Alien species, which can invade new habitats intentionally or unintentionally, tend to dominate the new ecosystem once successfully established.

Their threat to biodiversity is considered second only to habitat loss.

Dokrak said to cope with the threat of invasive alien species a list of the worst offenders should be compiled.

He said the country's current means of tracking the problem - by monitoring species using information from the Global Invasive Species Database - might not fit with the Thai situation.

This is because some species listed in the global database as invasive alien species are not invasive in Thailand, and visa versa.

For instance, he said, the Mexican Sunflower Weed is considered an invasive alien species in Thailand but does not appear on the global list.

"Where the Mexican sunflower weed exists no other plant varieties can grow.

"It's time to weigh up whether we should keep this flower to attract tourists or let it continue to eradicate native plants," he said.

However, in order to create a national invasive alien species list, intensive study is needed, Dokrak said.

All factors that contribute to the spread of these species their impact on new habitats must be collected and compiled.

Chawalit Wittayanond, a fish expert from the World Wildlife Fund, said the threat to biodiversity due to invasive alien species in Thailand was getting more and more serious and that new alien species are being discovered each year.

He said he recently found that the flower horn fish and bull frog, once exotic pets among Thais, in natural waterways.

"They are abandoned by their owners.

"If we do not do anything they might become invasive alien species," he said.