It seems to have become common practice to conflate ash dieback and Chalara ash disease. One frequently reads such statements as “ash dieback is caused by the fungus Hymenoscyphus fraxineus and was first found in native woodlands in Britain in 2012”. This ignores the fact that ash dieback has been a recognised problem in native woodlands for 70 years. In Forestry Commission Bulletin 62 (1984), Julian Evans wrote that ash dieback had been reported from the south Midlands since the 1950s, and was becoming more widespread. He referred to a 1983 survey that found some 22 per cent of ash in east central England to be subject to ash dieback. In a few localities, more than half of all ash trees were affected. Forestry Commission Fieldbook 16 (1998) described another serious outbreak of ‘ash dieback’ in East Anglia in 1992, which was characterised by crown thinning and twig and branch dieback, often culminating in death or in a ‘stag-headed’ condition. The dieback was considered to be stress related; living agents were not thought to be responsible.

The fungal pathogen Chalara fraxinea, now renamed Hymenoscyphus fraxineus, was first observed in the UK in 2012. It primarily infects and kills the leaves of young ash trees, though if it is allowed to penetrate the branches or stem it will eventually lead to dieback. Its modus operandi has some similarities to that of Diplocarpon rosae, the fungus causing black spot on roses.

There is now a voluminous literature on Chalara ash disease. One research project of special relevance to foresters and woodmen was published in 2014 by Dr Anne Chandelier in Belgium. In it, the concentration of air-borne Chalara spores in an infected stand was monitored as a function of height from the ground. A key finding was that few spores were detected at heights above three metres.

It is repeatedly stated that trees infected by Chalara ash disease will inevitably die, and that up to 90 per cent of the UK population of ash trees will be lost in coming years, at a cost possibly reaching £15 billion. It is suggested that the only hope for the future depends on identifying and breeding ash trees with greater resistance to the pathogen. Experience of Chalara accumulated over the last eight years in a young woodland here in Lincolnshire, however, presents an outlook that is very much less pessimistic.

This woodland is being established on former intensively cultivated agricultural land. The soil is far from optimum, varying from silt to heavy clay, and generally lacking nutrients except for a few small areas where manure heaps had been allowed to rot down. Testing has shown the soil was also heavily compacted. Planting of mixed hardwoods commenced in 2005 with ash numbering 125, about 10 per cent of the total. In 2006–07, an additional 150 ash were planted. Seedlings were obtained from about eight sources of supply. From 2014 up to the present, modest numbers of additional ash have been planted using wildings, resulting in a total of around 700.

Chalara ash disease was first observed at our Lincolnshire location in 2012 in a few trees in the now all-too-familiar form of dead leaves and branches and lesions in the main stem. It was decided at the outset to try to conserve the trees by reducing the height of the main stem to wood clear of infection, and also removing the lower leaves from the saplings in order to reduce the collecting area for fungal spores.

These conservation measures were instituted periodically and, over the course of time, crown-raising resulted in 4–5 metres of clear stem for older trees. The outcome has been remarkably favourable. Among the ash trees planted during the 15-year period 2005–20 there is a variation in vigour, as is inevitable. A small number are infected with Chalara, and are retained to ensure a source of infection. Less than 5 per cent of mostly weaker trees have died during the period.

Importantly, the woodland now contains a large population of healthy ash trees – including 80 prime trees, over 8 metres in height and 18 cm diameter at breast height – that have not suffered even leaf infections. Many trees have regularly set seeds. Factors that influence vigour (for example rooting environment and nutrient level) have been found to be important. Outstanding performance in terms of growth and freedom from disease has been demonstrated in a small copse of ash trees planted in 2007 that were fortuitously supplied in root-ball form.

Experience here shows that it is routinely possible to raise healthy ash trees by providing a modest amount of attention during the early years, aimed at raising the leafage to at least 3 metres clear of the ground. Mortality of young trees is normally less than 10 per cent.

The identification and breeding of Chalara-resistant ash trees as proposed by some will be a long-term process, but in the meantime, with appropriate management as indicated from our Lincolnshire experience, it seems certain that existing strains of ash can continue to flourish in our woodlands. Chalara may not be curable, but it is certainly avoidable.

Dr Roy Miller and Ian Willoughby,

The Marshes, Old Leake, Lincolnshire, PE22 9HZ


I write in response to the article in your December issue, arguing that wood should not be promoted for biomass to be burned for power generation (‘Wood “too valuable to burn”, says report’, Forestry Journal 316). I have previously featured in Forestry Journal as the owner of a small woodland in the Surrey Hills.

Some years ago, struggling to grow oak on land which 180 years ago was recorded on the 1846 Tithe Map as ‘poor arable’ but which had since borne a number of still present oaks of reasonable form, I became curious about the risk of depletion of nutrients.

Nutrients are substances required by both animals and plants in order to survive, develop, grow and reproduce. They are essential, but available and required in very different quantities. About 95 per cent of plant biomass (dry weight) is composed of the readily available elements carbon, oxygen and hydrogen. Other essential elements are nitrogen, phosphorus, sulphur, potassium, calcium and magnesium (referred to as macro-nutrients) and trace amounts of manganese, iron, chlorine, copper and zinc, as well as, in some cases, boron and molybdenum.

It is recognised that the annual harvesting of agriculture has trashed much of the planet, exhausting the nutrient content of soils. In the less developed world, they simply move on to clear another area of forest, while in the so-called developed world, we mask the result by industrial application of the macro-nutrients, producing foods that lack the benefit of the smaller trace nutrients, the role of which we do not fully understand.

As products of nature, our primary purpose is to reproduce and continue our species. A prerequisite is that we complete our early development and live long enough and healthily enough to achieve our primary purpose. Fundamental to that is that we are able to eat, and that the microbiome of our gut can cope with what we send to challenge it. We evolved eating what nature provided, which would have included the benefits of the smaller trace nutrients.

Since WWII, we have increasingly eaten products resulting from the industrial application of macro-nutrients; but from soil depleted of the rest. This change of diet, as well as the obsession with cleanliness and hygiene, antibiotics, increased chemicals in the home (e.g. fire retardants) and hermetically sealed, energy-saving homes with no fresh air, may well have led to deterioration of the microbiome of the gut and in turn to some modern diseases such as asthma, diabetes, obesity, and even damaged brain development in the most important first three formative years of the microbiome. A recent study found that one of the healthiest microbiomes was found in Irish travellers (BMA Horsley lecture, Dr Fergus Shanahan, 16 September 2020).

Forestry, with a harvest cycle of 50 or more years, has fortunately not reached the agricultural stage of nutrient depletion. However, the unnatural removal of tree materials from sites disrupts the fungally assisted recycling of nutrients that nature previously relied upon. Nature evolved accepting that the tree, containing nutrients taken from the site, would fall and decay in situ, releasing and recycling the nutrients, exactly where they are required, over the roots of the later generations of tree.

I had analysis carried out which showed that broadleaf tree leaves contain 50 per cent of the nutrient content they had in mid-summer, when they lose their chlorophyll and fall, yet our inclination is to sweep them up and burn them. Even with a sawmill on site, I calculated that if I only removed from the site sawn boards from the trunk, I was still removing more than 50 per cent of the nutrient content of that tree. As with agriculture, the problem is not so much with macro nutrients but the trace elements, some of which may no longer have a replenishment process, and the role of which we do not fully understand.

Nutrients are not destroyed if the material is used for construction. However, if the material is burned, the nutrients are destroyed and lost to the planet forever. At this point I ceased firewood sales to the local pubs, much to their disappointment!

The long-term negative impacts of destroying wood and other biomass by burning, and in particular deliberately growing fast-developing crops specifically for such destruction, on ground which may in future be required for food crops, have not been adequately examined. Nutrients are indeed too valuable to burn. That government subsidies encourage the destruction of such fundamental building blocks of life beggars belief.

Patrick Mannix

The Court House,

Shamley Green, GU5 0UB

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