Managing the  spread of wild rhododendrons

Ray Ryan reports on efforts to halt the spread of wild rhododendrons, which suffocate other species and pose a real threat to national parks.
Managing the  spread of wild rhododendrons

Oh to be in Doonaree

With the sweetheart

I once knew

To stroll in the shade

of a leafy glade

Where the

rhododendrons grew

Those are the opening lines of a country song penned by Eilis (Farrelly) Boland from Kingscourt in County Cavan some 63 years ago.

Dún na Ri is the historic name for Kingscourt and the song was made popuar by Ruby Murray, Vera Lynn, Eleen Donaghy and other singers.

The type of landscape which it praises still exists not just in Dún na Ri but in many other parts of the countryside including forest parks.

Each year, the rhododendron blossoms, adding beautiful colours to many parts of the land. But there is a less attractive side to the plant which was introduced into Britain and Ireland from Asia and the Iberian Peninsula in the 1760s.

It was planted on demesne lands for ornament, shelter and as cover for deer and fowl in woodlands. But it is now widespread on locations with varying climates from Donegal to south west Cork and from Connemara to east Dublin.

There are more than 900 species worldwide, but only one type (rhododendron ponticum) is invasive in Irish habitats. It blocks light, reduces biodiversity, suffocates other species and poses a serious threat to national parks.

As many as 7,000 seeds can be produced per branch and these are readily spread by wind. However, they can also be spread vegetatively, increasing its invasive potential.

Methods of eradication include removal from the root base, chemical spraying of stumps and injection of shoots with herbicide.

Thérèse Higgins pointed out in an 2008 manual on conservation published by the Irish Wildlife Service that in areas with sufficiently acid soils, and particularly where the mild climate allows, rhododendron has invaded woodland, plantation forestry and to a lesser extent, heath and bog.

In many places it has replaced the native shrub layer and grows in dense thickets excluding native vegetation below and limiting natural tree regeneration.

In order to meet the nature conservation objectives at sites, some management of rhododendron is required so that the status of native habitats may be improved. However, control is not straightforward.

Various agencies in Britain and Ireland have spent time and resources in attempting to control this plant and have found it an ongoing battle. Some of the most seriously affected areas are remote and in difficult terrain.

Rhododendron grows vigorously when cut, and is very resilient to herbicide treatments so that effective control requires very specific conditions.

With mature plants producing abundant seed annually, reinfestation of cleared areas is a significant hindrance to management. Many different approaches to the problem have been used, with varying success at different places.

According to the Inland Fisheries Ireland website, rhododendron ponticum is widespread in Ireland at present and is also becoming more common along the banks of rivers, particulary in the west, north-west and south-west.

“In these situations the dense growth adversely impacts on productivity in the river and impedes access to anglers or other water users,” it states.

Heritage Minister Heather Humphreys, in a written reply to a Dail question last year, said if left unchecked, this invasive species can grow in dense thickets and replace native shrub, exclude native vegetation and constrain native woodland regeneration.

Pointing out that the ultimate plan is to clear all rhododendron ponticum from national parks, she sad her Department is committed to continuing this important and challenging work into the future.

She paid tribute to the important contribution of volunteer groups to this work and the excellent work of her own Department’s staff in the national parks.

For more than 30 years, the National Parks and Wildlife Service (NPWS) has been working to eradicate rhododendron from the 25,000 acre Killarney National Park.

Fianna Fail TD John Brassil, who recently highllghted the problem in a Dail question, said rhododendron poses a threat to the park’s indigenous natural flora and fauna.

Minister of State Michael Ring said his Department is committed to tackling the spread of invasive species, most particularly rhododendron ponticum, the control of which is difficult, costly and labour intensive.

The management of the dynamic and aggressive rhododendron ponticum is a long-standing on-going programme in Killarney National Park, which, at this time, is composed of four elements.

Two of these are initial clearance and follow-up maintenance work by contractors and ongoing maintenance work by volunteers and students.

Another is an eradication management contract and ongoing work by the staff of his Department’s National Parks and Wildlife Service, including co-ordination, research, and monitoring.

Since 2011, his Department has invested over €700,000 to tackle rhododendron clearance in Killarney National Park and, in 2016 alone, spent some €210,000 on this work.

An updated strategic rhododendron management plan is being finalised and his Department hopes to publish this in the coming months.

Mr Ring said his department has an all-year round student volunteer programme for site maintenance and also runs four two-week work camps over the summer months. In addition, substantial areas are maintained and cleared under contract.

“In 2015, my Department appointed a specialist for a two-year period to assist the on-going Rhododendron ponticum eradication programme,” he said.

Having regard to the dynamic and aggressive nature of rhododendron infestation, he said the key deliverables of this contract include conducting an initial assessment of infested areas, having regard to available resources, and initiating early actions required for optimal impact.

It also involves implementing and producing a five-year management strategy for the continued eradication of rhododendron ponticum at various locations within Killarney National Park;

Other features include scientific investigations with a view to developing new measures for eradicating the problem.

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