Photograph by Patrick Pleul/DPA/Corbis

Yet another tree disease has reached Scotland.  Ash die-back which has already wiped out 90% of Denmark’s native ash population has now arrived.  The first site to be identified was at a new woodland at Kilmacolm.  Forestry Commission Scotland has now confirmed in a survey of 2730 ash sites in Scotland covering 49,709 miles, that 5% could be infected with ash dieback and will now be revisited for further inspection (Herald, 7th November 2012).

As well as ash die-back, there are at least another five imported diseases and pests now afflicting Scottish trees. A further 10, which could pose future dangers north of the Border, have also been detected in England and Wales. So far in 2012, four outbreaks of new tree diseases have been recorded in the UK – more than in any previous year. (Herald, 4th November, 2012). According to the Government’s Forestry Commission, the rocketing number of previously unknown diseases is creating “unprecedented threats”.  One Government scientist has warned of a “tidal wave of pathogens” entering the UK.

• Phytophthora austrocedrae kills juniper trees
• Dothistroma septosporum attacks pine needles;
• Phytophthora ramorum kills larch trees;
• Phytophthora lateralis kills the roots of cypress trees.
• Dendrolimus pini, a lappet moth is damaging pine forests

Five times more tree diseases and pests were reported between 2000 and 2009 than in the 1990s or 1980s. Experts blame the large increase on the expanding international market involving billions of plants.

“Increased global trade and tree imports pose a huge danger to our native trees,” said Dr Maggie Keegan, head of policy at the Scottish Wildlife Trust. “All too often novel pathogens end up in nurseries and garden centres and then spread from there into the wild.”

Ash is a key woodfuel tree and one that is being considered in Short Rotation Forestry (SRF) in Scotland.  However, now with a moratorium on planting, substitutes will need to be found, and Eadha believes that native aspen would be an obvious replacement.  Eadha is developing a network of local nurseries growing local provenance native trees for local planting projects.  This is a decentralised model of tree supply that creates a robust and sustainable model in the face of increased tree diseases.