Invasive species a threat to Sweden’s forests

The number of pathogenic fungi has increased tenfold over the last 200 years. The high rate by which new pests and pathogens reach Europe and Sweden is probably a result of increased global trade and transports.

Nursery stowaways

Half the number of new species arrives together with living plants. Plants planted in pots with soil from nurseries, constitute a major “villain”. It may be rhododendron bushes that, although they look healthy, are infected and carry a latent disease. The disease breaks out only after you have planted the rhododendron in your garden. Then, fungal spores can be carried on the wind, and infect native plants nearby.

“Algae fungus” on bilberry

A concrete example is Phytophtora ramorum, an “algae fungus”. Professor Jan Stenlid at SLU considers this fungus to be the most important new pathogen in Sweden. The fungus was discovered in the late 1990s in the U.S.A., where it caused the disease Sudden Oak Death in California. Presumably, the fungus has spread to the U.S.A and Europe via rhododendron bushes. In Sweden and Norway, the fungus was found for the first time in the middle of the 2000s. It has many host plants.

‘In the United Kingdom, this algae fungus has infected larch, and in Scotland, Wales and along the west coast of Norway it has been found on bilberry. I consider it a high risk that the fungus will infect Swedish bilberries as well,’ says Professor Jan Stenlid.

Emerald green ash-killer

Åke Lindelöw is an insect expert at SLU, and a member of the EPPO* Panel on Quarantine Pests for Forestry. The panel’s experts give advice to member states, based on risk analyses of fungus and insect species.

‘Six to eight new species of insects are now established every year in Europe. One of the new invasive species about to enter European territory is the emerald ash borer (Agrilus planipennis) that attacks and kills ash-trees. It’s an Asian beetle, now established in Moscow. It’s just a matter of time before it reaches Eastern Europe,’ says Åke Lindelöw.

Many insect pests are “imported” together with timber and the material it is packed in. All of the imported wood, also fuel wood – timber of low quality, should be properly controlled, emphasises Åke Lindelöw.

Biosecurity – what’s that?

Professor Jan Stenlid thinks that in Sweden we have taken the view that our ecosystems are in balance and have a buffering capacity. We have been spared, while other countries like Australia and New Zealand have experienced the detrimental effects of invasive species on the native flora and fauna. There is a much greater awareness among the public in these countries.

‘During a taxi ride in New Zealand, I discussed biosecurity with the driver. He was well acquainted with the sensitivity of the native ecosystems, and was able to discuss the negative effects of pests and pathogens at a species-level. We should be more aware of the risks in Sweden. In this country we don’t even have a Swedish word for “biosecurity”,’ says Professor Jan Stenlid.

Future strategies

Åke Lindelöw points out that when it comes to forest pests and pathogens, authorities have been very compromising with the trading sector.

‘To date, only the economic consequences and not at all the ecological consequences have been taken into account when assessing the effects of introducing alien species into Swedish forests,’ says Åke Lindelöw.

‘These are important issues to discuss. We have to develop a strategy for dealing with invasive species in Sweden,’ says Professor Jan Stenlid.

* European and Mediterranean Plant Protection Organization (EPPO). EPPO is a voluntary organisation with some 50 member states in Europe and the Mediterranean region. The goal is to protect plants and to develop strategies against the spreading of alien pests and pathogens.