MANAGEMENT
INVASIVE SP ECI ES
Rhodo Wars F
Find out how you can control invasive species like rhododendron in your woodland
or all its beauty, magnificent flowers, and undoubted den-making qualities, rhododendron (R. ponticum)
has to be considered a pest in British woodlands. Not only does it overwhelm areas it invades, but it also acts as a host for the Phytopthora ramorum fungal infection, which is the cause of Sudden Oak Death in the USA and has infected trees in the UK. According to Patrick McKernan of
Natural England, it was introduced to Britain in about 1793, probably from the Iberian Peninsular. It likes frost free, humid conditions and acid soils, and spreads through seeds and layering. And with 6000 seeds per flower head a plant can produce 1,000,000 seeds a year. Little wonder, then, that Forestry Commission Scotland has dedicated millions of pounds in an attempt to control the spread of evergreen plant from Argyll, where it is rampant. The problem isn’t solely Scottish, though the West Coast there does offer the perfect conditions for ‘rhodo’ to thrive. Great swathes of southern England suffer too, with the plant having a significant impact on biodiversity due to its dense shading, acidic litter and toxin-secreting foliage. The plants cleverly kill off any local competition to improve the chances of their own young regenerating. Rhododendron reduces
earthworms, birds and plants, halts tree regeneration, limits access and impacts upon woodland management. In coppice woodland like the Ashdown Forest of Sussex, where the High Weald AONB ran a Rhododendron Control Day in December, you have to fight the rhodo if you hope to restore the coppice. “Opening up woodland
08 Smallwoods Spring 2010
without a plan for rhodo control is a recipe for disaster,” said Patrick McKernan, who was speaking at the Ashdown Forest Centre. “Clear fells on Paws (Plantations on Ancient Woodland Sites) are very vulnerable.”
Controlling rhodo Rhodo control is achieved mechanically or by the use of herbicides, or more likely a combination of the two. You can get a contractor in to excavate the plants, which are then burnt, mulched, or chipped and baled for biomass. This raises issues of soil disruption, and on more sensitive, or smaller, or inaccessible sites the plants will have to be cut by hand or chainsaw as close to the ground as possible. There is
Rhodo
spreading in Ashdown Forest
also the option of winching plants out of the ground, but that can also have an impact on the forest soil profile and the ancient woodland seed bank of flora that will return once the rhodo is gone. There is also a risk that digging out the plants will damage mycorrhizal associations in the soil, which are critical to biodiversity relationships. And there’s a chance you’ll damage archeological features like charcoal hearths, saw pits and slag heaps from Roman times. Rhodo takes eight years to
establish before it seeds, and although plants produce huge quantities of seeds, the weak nature of the seeds means that it’s unlikely for persistent seed banks to become a problem. In other words, it is
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possible to permanently control rhododendron once you get on top of it, but the challenge is eradicating the stuff in the first place, and then making sure the root systems don’t sprout again.
Stem control To control the stems Patrick McKernan says that you have to spray with herbicide within 10 minutes of cutting. His advice is to cut high first to remove the bulk of the branches, then cut low and treat. He says that Forest Research are currently conducting trials injecting stems with 25% glyphosate solution. Follow-up spraying is best done in the second summer after a winter cut, but for owners of small woodlands
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INVASIVE SP ECI ES MANAGEMENT
Controlling Hugh Prendergast offers clearance tips based on experience with rhododendron in Ashdown Forest
R. ponticum is a wild plant, and will spread quickly. In Ashdown Forest they've been using excavators to pull our plants by their roots
• Use a combination of volunteers and contractors. • Start any clearance of rhodo on an edge of smaller plants as the bigger plants will need mechanical extraction the following year. The smaller ones are easier to control and efforts can be concentrated at the ‘front’ at the beginning. • Do not forget the seedlings. The survival rate may decline, but you can have a lot after five years. In Ashdown Forest they’ve pulled up about 8000 seedlings in areas cut in 2004-5. Soon they’d too big to be pulled up.
Patrick
McKernan of Natural England spoke of some of the ways to eradicate rhododendron at a special training day in Ashdown Forest in December, organised by the High Weald AONB at the Ashdown Forest Centre
Spring 2010 Smallwoods 00
photo: fc photo library
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