Making your way through a jungle of 12 foot high vegetation wielding a machete is not something you expect to be doing on Harris! Harris is better known for its open vistas, white beaches and rugged moorland. However, in the first week of September we were battling with an alien invader – Giant Rhubarb (Gunnera tinctora). Giant Rhubarb is an invasive plant species native to South America that was first introduced to Harris as an ornamental garden plant around 20 years ago. It thrives in our mild wet climate and wet peaty soils and has spread out of gardens, onto crofts, road sides and into water courses. Its leaves can grow to 2.5 m across which shade out and out compete our native flora. Its fruiting bodies are in the form large cone shaped structures each of which can hold up to 80,000 seeds that are spread by birds, wind, and water courses. It also spreads through the ground by a network of Rhizomes.
In recent years concern about its spread has been raised by local residents and as a result we are trialling various control techniques guided by advice from an Irish eradication project with the aim of refining and expanding our efforts next year. With the help of a group of enthusiastic John Muir Trust volunteers we set to work, cutting and digging out plants. We dug up some of the smaller plants and with the larger plants we were cutting the leaves and stems down to the rhizomes. We were then spraying the cut stems with herbicide and stabbing the rhizomes with screwdrivers followed by herbicide injection into the rhizome. Away from water courses we also sprayed the leaves of some plants. All seed heads were also removed to prevent their spread. When there was some breeze to keep the midges away, removing these plants was really quite satisfying. This was also a welcome opportunity to be re-united with my machete which had been in storage since returning from an expedition to the jungle 10 years ago. We made good headway in the area around Urgha, at Rhenigidale and Scaladail. However the scale of the problem is such that it will take several years before we start making a big difference in the areas worst affected. Globally, invasive species are one of the greatest threats to biodiversity, along with climate change and habitat destruction. Therefore, the spread of Giant Rhubarb offers a real threat to our native species and one that we are taking seriously.
The enthusiasm and commitment of the JMT volunteers was much appreciated and it is hoped that this will be the first of several Giant Rhubarb control work parties.
If you are concerned about the spread of Giant Rhubarb in your area in your area we would be interested to hear from you.