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Why is it invasive in Ireland?
Last updated: 17th November 2009

There is no one straight forward answer as to why some plants become invasive while others don't. But there are certain characteristics and factors that can help a plant thrive in a particular place. It has the ability to reproduce both seed and fragments of the rhizome. Gunnera produces large quantities of seed which can be transported by birds and other animals, by water and by falling next to the parent plant. The fact that it can reproduce from a piece of rhizome means that any disturbance to an area with Gunnera can make the problem a lot worse and pieces can be moved along by machinery.
Gunnera can grow to over 2 m tall, meaning that compared to most Irish native species it is very large additionally it starts its growth of leaves early in the spring, easily shading out other plants. Due to the ability to fix nitrogen from the atmosphere it means it can grow in fairly nutrient poor soils, where other plants may struggle to live. It is found to grow in almost complete gravel where it appears nothing else is able to grow. The climatic conditions found on the west coast of Ireland are similar to those found in its native country. It is native from the southern parts of Chile and Argentina where there is high rainfall and mild winters.
Even though Gunnera was introduced in Ireland possibly over 100 years ago, it only seems to be a problem recently, this is true of many invasive species that show exponential growth curves. As when it is first introduced there are only a few individuals and it takes many years for the population to grow to large numbers, and the problem becomes apparent. It is also possible that climatic conditions may have slightly changed, allowing for higher germination rates than previously. There is also the factor or land use changes, while before there was more agriculture and management of fields, keeping weeds and invasive plants in check, while now there is large number of land abandonment and building of holiday homes, allowing unwanted plants to become established.

Robin on a Gunnera plant, helping the long distance spread of the seed

Field left unmanaged invaded by Gunnera neighbouring grazed fields

Gunnera completely invading a quarry, the movement of contaminated soils is aiding the spread of this species.