Most people interested in woodlands will now be well aware of the latest threat to our woodlands, but what might it mean in practise for small woodland owners? To date the disease (Chalara fraxinea, to give it the scientific name) has only been found in mature trees in the east of the country, but is being tracked to many more new planting sites that have used imported stock. The current effort is to identify and eradicate the young infected stock, but a recent national meeting of experts has concluded that there is currently little that can be done to stop the spread in older woodland. This is partly because ash trees are found throughout farmland, including in regularly flailed hedgerows, making eradication extremely difficult.
The disease has many echos of Dutch Elm Disease, brought into the country in the 1970s, which virtually eradicated the elm tree in this country. However, there are some important differences. Chalara fraxinea is a fungus, spread by as spores by wind, whereas the fungus that caused Dutch Elm disease was spread by the Elm Bark Beetle. Also Ash trees have a much greater genetic diversity than the elm, which spread by suckering rather than seed. That has led to suggestions that there may be a much better chance of immunity for our stocks of native ash.
However, losses are hard to predict, and the best guess figures we have heard is that perhaps 95% of trees will succumb and die to the disease, but other survive due to natural resistance. Mature trees may take several years to die after first becoming infected. Indeed current surveys show more and more sites where infection has occurred, and probably been present undetected for several years. Early symptoms to spot are leaves wilting and then turning black and shrivelled well in advance of the normal autumn season. The Forestry Commission web-site has comprehensive details.
Providing there is some immunity, the ecology of the woodland will survive pretty well, especially older woods. However, younger plantations are likely to have closely related plants, and may suffer almost complete losses. If you depend on your woodland for income, the result is more severe, as infected trees rapidly stain and lose commercial value. Felled early enough firewood remains an option, but is not always the most valuable crop, and many woods will require premature felling.
So, what might it mean in practice for small woodland owners in the south west?
- If you have young stock planted in the last five to seven years, check them regularly for symptoms. If you see anything suspicious report it to the Forestry Commission.
- Current estimates are that the disease may take 10 to 20 years to reach mature woodlands in the far south west.
- We expect timber and firewood sales to remain possible, but markets are likely to be adversely affected. Firewood prices may fall, but other government policies to increase the use of biofuels require a big increase in production, so this may not happen.
- Leaves and twigs are the main source of infection, so they should not be taken off site. Do not allow any infected trees to be put through a woodchipper, or taken off site to use as mulch.
- In our own woods we are already adapting our thinning regimes to select against ash and in favour of other species in the woods. This will help mitigate the later effects of infection and tree loss.
- We would not currently recommend planting ash in new woodlands. We hope that resistant strains will be found and propagated in due course. Current best practice is to include several species in any new planting, to help proof a wood against both climate change and potential disease threats.
The situation will change rapidly in the coming months and years. However, the response of Government has excellent in the last few weeks, although officials were slow to react in the first months of the outbreak being discovered in tree nurseries. In the last three years there has been some practise with the response to Phytophthora ramorum spreading through larch plantations. And with memories of Dutch Elm Disease, then no-one in the industry is going to be complacent.