The visual impact of invasive species is nothing to the damage done to our countryside. By Marie Louise Heffernan
There is a wave of immigrants occupying land in Connemara. They are not to be welcomed. These are plants which are not native but have escaped in this area. Some such as the Himalayan balsam and the Rhododendron have beautiful pink flowers in summer and add a splash of colour to the landscape. Others such as the false rhubarb colonise stretches of roadside with their prickly umbrella leaves and are truly unsightly. However the visual impact is the tip of the iceberg and whether or not we like them, we must recognise the threat they pose to our landscape and ecology.
Rhododendron ponticum is the most invasive of these alien plants we have in Connemara; it thrives on the acid soils, spreading over our bogs and threatening native forest habitats. Like many of these exotic invaders it was brought in as an ornamental shrub from Asia during the Victorian era. In north west Connemara the main source of rhododendron is Kylemore, which is spreading throughout the beautiful woodland planted by Mitchell Henry in the 1800’s.
Rhododendron kills woodlands as its waxy leaves form a toxic layer which no other seedling can germinate in. They take root once their branches touch the ground, forming a tangled impenetrable mass. These plants spread easily over bogs and heaths such as at Killary Harbour. They have no native predators which add to their success in this environment. Their toxic leaves are unattractive for insects and so no birds nest or sing in these barren thickets.
Woodlands that should be alive with song and carpeted with bluebells are quiet.
Even the nectar is toxic. In a recent study published in Functional Ecology, research led by the Trinity botanists shows that Rhododendron nectar is extremely toxic to native honeybees.
Rhododendron and Gunnera are the most obvious of these unwanted aliens. Gunnera tinctoria is a plant native to South America. It is also known as false rhubarb as it has similar leaves to the common edible rhubarb. It was introduced to Ireland over 100 years ago, again as an ornamental plant. Its natural habitat has very similar climatic conditions to those found in the west coast of Ireland. In Connemara, Gunnera is found mainly along roadsides and waterways, on coastal cliffs and disused farmlands and quarries. It has now begun to spread into fields too, covering large areas.
Our controversial N59, which is normally a visual treat for tourists and locals in summer with ox eye daisy, meadow sweet, purple loosestrife and heathers on edge is, in sections, now dominated by this huge prickly perennial. It spreads easily by seeds and fragments can easily regrow into full plants. Although it is believed by some to be poisonous to touch it is not – but beware of its prickly stem. Another roadside plant is the Knotweed.
Here in Connemara we have at least three different knotweeds – Japanese knotweed, lesser knotweed and greater knotweed. The Japanese knotweed is probably the most controversial because of its powerful growth. Japanese knotweed was introduced as an ornamental species in the 19th century from Japan. It has red zig zag stems and a hanging spike of white flowers in late August or early September. It is found alongside roads and rivers. It is not a toxic species and in fact in Japan is frequently eaten and apparently tastes like rhubarb.
However, don’t let its sweet taste disguise its deleterious impact. It spreads from the smallest fragments and can colonise large areas. Rivers that should be edged with alder, irises and a diversity of wetland species are dominated by knotweed.
It is an incredibly strong plant and can knock walls and undermine houses. It can push its way through tarmac. I have recorded it at Roundstone Pier and recently at the old wall behind the former workhouse in Clifden. It would be such a shame to lose our heritage to this plant.
So, what is being done? Well the National Roads Authority (TII) has decided to take action on invasives on the main roads and this is certainly to be welcomed. In Letterfrack Ger O’Donnell of the NPWS is planning on an assault on Rhododendron within the park and is joining forces with Letterfrack Tidy Towns and Connemara West to control knotweed (lesser) and Gunnera in the village.
However, given the rapid rate of spread of these species we would all want to take action. Certainly small plants can be pulled up, but generally for these species herbicides are recommended as best method of control.
This time of year is the optimum time for Gunnera and Knotweed control. Glyphosphate or roundup can be used effectively. Gunnera leaves may be cut off and the stump treated immediately with herbicide. Do not cut either these plants as the many fragments can regrow into individual plants.
Rhododendron can be sprayed if the plant is less than 1.5m high and if taller it should be cut to stump level and immediately treated with herbicide.
However, do remember that herbicides are toxins and must be applied in correct concentrations, carefully and under good dry conditions.
Further details on control of these plants may be found on invasivespeciesireland.com.
Together we can stem these land grabbers in Connemara.
Letterfrack Tidy Towns will be looking at invasives in October as part of the Green Festival www.connemaragreenfestival.ie