Tag Archives: garden

Citizen Science and Biodiversity: Thoughts From a Meeting With the European Citizen Science Association

Image Credit: NPS Photo, CC BY-SA 2.0

A collection of biodiversity researchers from across Europe came together in Brussels for a unique kind of meeting last week. We were connected by two common threads: first, we are all supported by BiodivERsA, a large network of European biodiversity research projects funded by the European Union’s Horizon 2020 program. And second, most importantly, we are all interested in connecting our biodiversity research with citizen science in one form or another.

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The Common Ragweed

The common ragweed, set to become a nightmare for hayfever sufferers

Image Credit: Sue Sweeney, CC BY-SA 3.0, Image Cropped.

In this series, we’ve already learnt about the impacts of alien trees and garden plants in Norway, but others are invading too, including some that are easier to overlook. And some of them can not only out-compete native species, but also pose health problems for humans. In today’s guest post by Vanessa Bieker, we look at Ambrosia artemisiifolia (common ragweed), which produces highly allergenic pollen and is one of the main causes of hay fever.

What is it?

Common ragweed is an annual wind pollinating weed that comes from North America, and was introduced to Europe in the late 19th century. Today it is found on every continent except Antarctica. It is established in South Europe (etc. France, Italy, Hungary) where the climate is more similar to that in its native range, but it is spreading further north. By 1996 it had reached Sweden and it has now spread to Norway, although it seems that it is not able to reproduce here yet. This is likely to change in the near future due to a warming climate and its ability to adapt. The plant dies with the onset of frost, but seeds can remain viable in soil for at least 40 years. Common ragweed normally germinates in April and grows rapidly. It can therefore out-compete other plants. Fully grown plants can be between 30 cm and 2 m high. A single plant contains both male and female flowers and is able to self-fertilize. Thus even a single plant can give rise to a whole new population. The plants tolerate damage quite well, they have the capacity to regrow and produce flowers even after mowing.

How did it get here?

A. artemisiifolia is usually found in disturbed habitats such as abandoned fields, along roadsides, at construction sites or in private gardens. The ragweed can be spread in many ways, from harvesting or mowing machines, to the spread of compost that contains ragweed plants.  The seeds seem to be rather heat tolerant and can survive composting. As the seeds can float, dispersal through water streams is also possible. The main vector into new ranges is probably from contaminated seeds imported from North America, especially sunflower and bird seeds. About 70 % of birdseed mixtures are contaminated with ragweed seeds, which are often able to germinate.

What does it do?

Bad news for people already suffering from hay fever: due to the late flowering of ragweed (August – September), the pollen season expands. Because the size of the pollen is extremely small, it can be carried by wind several hundreds of kilometers. And a single plant can produce quite a lot of pollen (up to 2.5 billion grains per plant per day). So it’s best to get rid of the plant before it starts to flower. This will also help preventing it from spreading further. If you want to get rid of ragweed in your garden, it’s best to wear gloves as it can also sometimes cause dermatitis even if you’re not suffering from hay fever.

But there is not only the problem for people with hay fever. Ragweed is also a huge pest in agriculture as it causes immense yield losses (up to 30 % in soybeans).


This is legitimately the only decent free-to-use photo I could find when I googled hayfever. I wish I looked this good when I sneezed, and not like you’re alcoholic uncle with mussels for eyes. (Image Credit: Needpix.com)

What to do about it?

Common ragweed is still pretty rare in Norway, but actions against it should already take place before it manages to become established here. Once an alien species is established and widespread, eradication can be very difficult (or impossible) and rather expensive. Ragweed for example can build up a seed bank relatively fast. Most of the seeds produced in one year will germinate in the following year, but some seeds remain in viable in the soil. So if no seeds are produced in one year (because the season was too short or the plants were removed before flowering), those remaining seeds from previous years can germinate in upcoming years and thus keep the population alive.

A good way to get rid of ragweed is by uprooting the plants. As they have a high ability to regrow, those plants should be stored without contact to soil. It’s best to do it before plants start to flower to prevent pollen production and reproduction, as contact with ragweed can lead to skin irritation, gloves should be used.

If you suspect that you have found common ragweed, you can use the following webpage to help you confirm it:


If you would like to know more about common ragweed, we invite you to read the following articles:



The Spanish Slug

When I was 12 I read a book which involved an encounter with terrifying mutated slugs that fed on birds. So you can imagine my horror when 17 years later, I came across the Spanish slug, which is capable of terrorising bird nests. In our latest article of Norway’s invasive species, we look at what other forms of havoc this slug wreaks.

What are they?

Considered the most destructive pest slug in Europe, the Spanish slug, or Arion lusitanicus, or Arion vulgaris, or sometimes Geoff (there’s some controversy over the name, thanks to the fact that the Arion genus contains up to 50 species and they all look a lot like one another) is between 7-15cm long and can weigh up to 15 kilos if it’s sitting on a dog. They were originally thought to be from the Iberian peninsula, hence their name, but it appears that the slug doesn’t appear in Spain anywhere south of Catalonia, a controversy which recently ignited political unrest throughout the region. They are an incredibly slimy species, leaving trails wherever they go, however identification upon sight is made difficult by the fact that they can be a variety of colours, including yellowish, grey, reddish or brown, as can many of there aforementioned close relatives.


When it comes to appearance, the Spanish slug is only as gross-looking as any other slug (Photo Credit: Mogens Engelund, CC BY-SA 3.0)

How did they get here?

Geoff can now be found throughout the whole of Norway, with the exception of Troms and Finnmark. Soil and plants are the slugs food source and egg-laying sites, which means that potted plants have spread them throughout most of Europe. They don’t seem to discriminate between urban and natural habitats, which mean they can pop up pretty much anywhere. Those guys you seen covering the paths at twilight every day? Probably them.

What do they do?

They eat birds. Yeah I wasn’t joking about that. In a recent review of Geoff’s attack on birds, injuries of nestlings included “bleeding wounds, holes in the stomach with viscera exposed, vast skin lesions on wings, back, neck or head, partially eaten muscles or bills, even loss of eyes”.

But whilst horrifying, I should not pretend that this is one of the major threats the slugs pose. They are more likely to cause declines in native slug species before we see any impacts on bird populations. However they are a real threat to Norwegian crops. Like many successful invasive species, they will feed on a wide range of organisms, so while there has been no quantitative study on the economic impact of the slugs yet, there have been reported attacks on everything from potato fields to garden plants to sunflowers.

How do we stop them?

Prevention is almost impossible, as this would involve detailed inspection of all imported plants, which would potentially do little damage to a species which is already well established in Norway.

It is possible to reduce local populations by killing slugs. Decapitation or storage in the freezer are effective methods. Use of homemade explosives is considered excessive, and to be honest if that’s an option then you’re overqualified for pest removal. Elimination of eggs is also recommended, and slug fences (see here for an example) can help keep them out of garden patches. However the techniques are small-scale and labour intensive, and therefore not particularly helpful for the agriculture industry.

On a wider scale, some foreign parasites and beetle have been introduced as control measures, and slug pellets and other molluscides have been used in Europe. However the effectiveness is not proven yet, and some may have negative impacts on native species, and many molluscidal compounds are banned in Scandinavia.

For more information on the Spanish slug, we invite you to read the following studies

Invasive Alien Species Fact Sheet – Arion vulagris by the Online Database of the North European and Baltic Network on Invasive Alien Species

Arion slugs as nest predators of small passerine species – a review by Katarzyna Turzanska and Justyna Chachulska

Invaders in the Garden

The Japanese Knotweed, an invasive species often found in gardens (Image Credit: HOerwin56Pixabay license, Image Cropped)

Guest post by Malene Nygård

Garden plants have a long tradition in Norway; from being used as medicine and food in the gardens of Catholic monasteries in the Middle Ages to today’s exotic ornamental plants. But this tradition also represents several centuries of unmonitored introductions of alien species, and it has left its mark in Norwegian nature.

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