Control of tree mallow

Control plots on Craigleith that were set up to monitor the sucess of cutting as a control strategy.








Management Options

Latest news on management

Managing tree mallow on seabird islands

This project sets out to develop a sustainable management strategy for seabird islands around the UK that either currently have extensive tree mallow stands or are at risk invasion of this species in the near future. Specific management options for Craigleith, the most affected island, are briefly outlined below.

 Management options on Craigleith
Should anything be done about the spread of tree mallow and the declining puffin numbers on Craigleith? If yes, what could be done?
Practical solutions need to be developed and tested, if biodiversity on those islands currently dominated by tree mallow is to be restored and if biodiversity loss on islands where establishment is at a less advanced stage is to be prevented. The following options are being discussed:
No intervention at all
One of the options is to leave tree mallow and puffin populations on Craigleith on their own. We could then see how their populations develop without any direct human intervention, with the possibility that puffins might disappear from the island.

Cutting tree mallow
A preliminary study suggests that cutting and removing tree mallow on Craigleith helps puffins to find spaces to build their burrows. However, removal of tree mallow may lead to soil erosion, especially during winter and spring. Solutions have to be found that prevent the soil from being washed into the sea. Whereas cutting plants with shears is highly effective in eradicating the fully-grown plants, seeds which are still in the soil germinate rapidly. Cutting has thus to be repeated for several years in a row, several times a year.

Introduce neutered rabbits
Studies in other areas indicate that rabbits reduce tree mallow numbers as they feed on the young plants. Currently, there are no rabbits on Craigleith though there were in the past. Rabbits could be re-introduced on the island. However, the development of a sizeable rabbit population may cause soil erosion due to the burrowing activities of the species. Therefore, introduced rabbits have to be neutered before being placed on Craigleith.

Spraying of tree mallows
Spraying tree mallow with herbicides might be a less labour-intensive way than cutting to reduce tree mallow on Craigleith. The herbicides would only affect plants with broad leaves such as tree mallow, but not grasses.
As these herbicides decompose very quickly, they would not have negative impacts on soil or water quality. However, spraying has to be repeated various times per year and over several years in a row as plenty of seeds are still in the soil.

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Tree mallow plant Tree mallow plants Dense stand of tree mallow

Varying density of tree mallow invasion. Success of removal is likely to be highest where the density of plants is lowest.