Dealing with invasive rhododendron
In flower, it can look pretty, but Rhododendron ponticum is extremely invasive in our rainforests. Credit Caz Austen / WTML
Rhododendron ponticum is a particular type of rhododendron that’s widely recognised as a major threat to Scotland’s rainforest. We’ll refer to this species as ‘rhododendron’ in this guidance, although there are many types of rhododendrons in cultivation that do not currently threaten the rainforest. It has evergreen foliage and grows densely, shading out native tree species as well as rare bryophytes and lichens. Rhododendron can also host a pathogen that is lethal to some other tree species.
Rhododendron is very persistent and produces large quantities of seed once mature. Therefore, rhododendron is a shared problem for everyone managing land in flying distance of its seed, and clearing this invasive plant from an area should be done at a landscape-scale, ie whole-catchment or peninsular-scale. Effective management involves removing every single plant of rhododendron and then actively preventing re-invasion in subsequent years forever thereafter (see Rhododendron report).
Rhododendron control is difficult and expensive. Furthermore, resource is likely to be wasted if it is not done at large enough scale and/or without a clear plan for preventing re-invasion in the longer term. Work at the whole-catchment or whole-peninsula scale will nearly always involve landowners and land managers collaborating across land ownership boundaries.
Even the best clearance techniques will not eradicate rhododendron in one treatment. Credit John MacPherson / WTML
What management is needed to combat this threat?
Seek advice from specialists and learn from people who have already done collaborative rhododendron work when planning projects.
Find out who else in your area is dealing with rhododendron. Rhododendron control must be part of a strategic landscape-scale management plan, and strong partnerships with neighbouring estates and the local community will be essential to make sure that there will be coordinated action. This may also increase the likelihood of attracting funding for rhododendron control.
A broad understanding of how much and where rhododendron occurs on your property and neighbouring estates/wider catchment area is useful as part of initial scoping work. A more detailed survey is usually required for a full conservation management funding bid, so that work on practical removal can be fully planned and costed.
The services of appropriately qualified contractors should be procured to carry out this work where necessary. They will be following best practice guidance for removing rhododendron and choosing the most appropriate technique for your property. The stem injection method is proving effective and has the advantage of reducing the amount of chemical entering the environment. Please note that Buglife do not endorse the use of glyphosate for any purpose.
Even the best rhododendron clearance techniques will not eradicate rhododendron in one treatment. Follow-up work to remove seedlings and any re-growth from cut stems will be required. Land managers will need to make a long-term and on-going commitment to the ‘maintenance phase’ of rhododendron control.
Ongoing monitoring for rhododendron regrowth and any remaining plants across the whole landscape area means that action can be taken before the rhododendron becomes a major (and costly) problem once again. Monitoring needs to lead to targeted follow-up treatment.
Rhododendron clearance work and follow-up needs to be coordinated across the landscape/catchment area. Neighbouring landowners need to be made aware of what work is going to be happening, where and when so that they can implement their own removal strategy effectively.
Regular monitoring could be an opportunity for the local community to get together and work to defend and protect their landscape from repeated invasion.
This landscape approach also applies to other invasive non-native plants that pose a threat to Scotland’s rainforest (see guidance for delivering invasive non-native plant control projects).
