Why Rhodo is a no-no for Killarney

SOON, the deep red and purple hues of rhododendron will light up the summer landscape but the beauty of the plant conceals the fact that it has become a pest in many areas and literally stifles the life out of other growing things.

Picture postcard photographs of Killarney National Park, for example, feature the rhodo in glorious bloom. According to the park authorities, however, it presents what is probably the biggest conservation challenge facing the park.

It is ‘rampant and invasive’ and upwards of 650 hectares of National Park land are completely infested. Light cannot penetrate the dense thickets of rhododendron, with the result that very few plants can survive beneath it.

Even the cherished oak and yew woods in the park are in long-term danger as they will not regenerate if the rhodo takes over. For that reason, the National Parks and Wildlife Service (NPWS) has an programme to control and eradicate it.

This work is highly labour intensive and involves thorough clearance of affected areas. Voluntary workers take part in Groundwork schemes during the summer and they make a valuable contribution.

If it is allowed to spread, rhodo can also cause damage to important farmland habitats, woodland, bog and heath. Farmers or landowners who are in receipt of Single Farm Payment, along with people taking part in agri-environment schemes must avoid infestation of their land.

This non-native species was originally planted in gardens from the 18th century, and on the edges of estate woodlands and moorland to provide cover for game. The impact of its dark, evergreen canopy and toxic leaf litter has produced a sterile zone underneath, where native species have been unable to compete.

Rhododendron is poisonous to mammals and insects, and is generally avoided by grazing stock. As few as three leaves can be fatal to sheep and goats. Chemicals are released into the soil, further reducing native plant species and affecting insect, mammal, and bird populations.

When cut down, the rhodo roots can regrow very quickly so control by immediately painting the freshly cut stumps with a herbicide solution.

When mature, plants produce over a million wind-blown seeds each year.

Rhododendron is a host for the serious plant health disease “sudden oak death which can wreak havoc on important woodland, bog and heath habitats.

Killarney has more than 400 hectares of oak and yew woods – believed to be the last remnants of ancient, native Irish woodlands – and the NPWS has been running a project in recent years to protect these woods from the plant.

A study by JR Cross, of the TCD School of Botany, confirmed the rhodo is a ‘serious threat’ to what he described as the most extensive semi-natural woods left in Ireland because it spreads so rapidly and can so easily invade new areas. For such reasons, there are real fears the rhodo could lead to the long-term destruction of the Killarney woods.

Thanks to a new system of clearing the National Park of the rhodo, new oak, holly and other trees are growing in areas once completely overgrown by the rhodo, including Tower Wood and Lower Derrycunnihy.

The plan is being put into effect in sections of the park with the aim of allowing the largest remaining native oak woods in the country to regenerate.

Previously, grazing animals could come into areas cleared of the rhodo, thus preventing the woods from growing again. But, under the new system, fences made of rhodo foliage are put up around cleared areas, keeping deer, sheep and other animals out.

Dubbed ‘dead fencing’, the fences are up to three metres in width and about a metre and a half in height. Formerly, when rhodo was cleared in an area of the park it was burned, or left to rot on the ground, but all the foliage is now used in the fencing.

Deer need a firm footing, but when they stand on the foliage it has the same effect as a cattle grid. Another positive aspect of the dead fencing is that is provides additional habitat for birds and insects.

Rhodo eradication work has been going on in Killarney for close on 30 years, but that has not stopped the rhodo from regrowing in some areas that had been cleared. As well as that, many new areas have since become infested.

The eradication process takes several years to complete and needs regular monitoring.

Globally, there are upwards of 800 species of the rhodo which is particularly prolific in America. It covers around 12,000 square kilometres in the Southern Appalachians and is on the state flag for West Virginia and Washington.