Difficult choices to protect gardens and the environment

Katy Hayden, Royal Botanic Garden Edinburgh

Today it was reported that Arduaine Garden in Argyll will fell about 900 Japanese larch trees in an effort to prevent the spread of Phytophthora ramorum. 

Heritage gardens play an important role in plant conservation. They house collections gathered over decades or even hundreds of years, including varieties of plants that may be overlooked elsewhere, fostering heirloom varieties and preserving biological diversity that is the raw material of adaptation. As well as being beautiful and tranquil sites of cultural heritage, these ex-situ resources are treasure troves of biological diversity. Arduaine Gardens shows us that tough choices can be necessary and important to preserve these collections and the surrounding environment.

Starting this autumn, Arduaine will begin felling the 900-some Japanese larch trees (Larix kaempferi) within the garden’s shelter belt. Among these trees were the first finding of the invasive pathogen Phytophthora ramorum in Scotland, and despite selective felling of infected trees since then, and continued efforts by the Forestry Commission Scotland to fell larch wherever infections occur, the disease has spread.

Until 2009, Phytophthora ramorum was known as a disease of hardwoods and ornamental plants. Something shifted, however, and the pathogen is now an extremely effective pathogen on larch, producing many more infectious spores on larch than on any other host species, and with Japanese larch the most susceptible species. This most likely means that epidemics in larch trees are more infectious than in other hosts, and may explain why the disease is continuing to expand in Scotland, even into areas that are less favourable for the pathogen. Until last year, the only known occurrences of P. ramorum on larch were in the British Isles, but it has since spread to Brittany.

Because the sporulation potential is so great on larch, felling all Japanese larch in the shelterbelt at Arduaine makes good sense. Larch can act as an amplifier, catching spores of P. ramorum and then pumping out more, which can go on to infect other species. Beyond the larch themselves there the incredible Rhododendron collections in the garden, oaks in the surrounding woodlands, and perhaps other species that would become hosts in the presence of a high enough spore pressure. By taking this seemingly drastic step, the garden is protecting its collections and helping to lessen the spore load in the area overall, ultimately protecting the wider environment. 

For more information on this story visit the BBC news website.