Tuesday, November 27, 2012

The ash dieback debate develops

I continue to follow, albeit rather wearily, the ash dieback debate through many authors in newspapers, magazines and blogs, both here and in other countries.

There now seems to be a general consensus that infection is by wind borne spores and there is little that can be done to stop the progress of the disease.  It is thought like that up to 10% of ash trees will be resistant to the disease and that these may be an important resource in ensuring the ash's future recovery.

There has also been much debate about the pros and cons of large tree planting schemes and it is frequently pointed out that Britain has proportionately less woodland cover than almost anywhere else in Europe.

This has brought the issue of natural regeneration rather than deliberate planting to the fore.  In East Sussex where I live I know of many places, usually abandoned fields, that have regenerated to secondary woodland surprisingly quickly and, judging by the size of the saplings I have seen in some televised tree planting schemes (maybe only from seed this year), regeneration may be almost as fast, if not faster than planting.  Though it does not do much for the tree nursery trade, or other human engagement with tree planting schemes.

I think the regeneration point is well-illustrated by this  from Julian Roughton as a comment on a Guardian article: In 2005 Suffolk Wildlife Trust bought a 40 acre field alongside an ancient woodland reserve - no trees were planted to see what would naturally emerge. Now there are something like half a million young ash trees many ten feet tall as well as birch, oak, field maple, hawthorn and blackthorn. Despite no tree planting thousands of young ash saplings are now affected by ash die back. Hopefully some of those half a million young ash trees will emerge with some resistance but where they die other tree seedlings are likely to take hold.

There also seems to be a conflation of trees with woodland.  We cannot have woodland without trees, of course, but woodland is much much more than just trees.  Not only does it have important open spaces like glades and rides, it has something known as an edge ranging from almost bare ground through shorter grasses and herbs to scrub and various shrubs unlikely to survive in closed canopy conditions.  This woodland edge often contains the greatest biodiversity and is much loved by species like  nightingales, dormice and pearl-bordered fritillaries, all species often associated with woodland but preferring scrub and more open areas.  There are also many species that spend part of their life within the tree canopy and part in the sheltered sunshine of the woodland edge.

The chair of The Woodland Trust, Clive Anderson, pointed out is an Observer article yesterday that with natural regeneration "It can take a while for trees to force their way through grasses, low-growing plants and scrub, but they will get there in the end."  True maybe, though self-sown trees, as I said above, can grow very quickly.  However, grasses, low-growing plants and scrub are just as much part of the natural environment, and just as important to wildlife as woodlands.

As has often been remarked, nature is dynamic and is constantly undergoing change and alteration.  Woodland may be termed climax vegetation but trees eventually die and the space is created which is the other side of the forest coin.  I have long thought that we are failing to appreciate the diversity and complexity of wildlife if we compartmentalise the landscape too much: that is a wood, that is a heath, that is a field.  Until recently housing or commercial developments were allowed to go right up to the edge of an ancient woodland, but now a buffer of 30 metres or more is often specified.  This buffer is to provide a wonderful mixed edge of "grasses, low-growing plants and scrub" on which the life of the wood is partly dependent.

It would be silly to suggest that all tree planting schemes should stop, but it would be nice to see more natural regeneration schemes such as that by the Suffolk Wildlife Trust mentioned above being promoted, studied and discussed.  If a field were to become available for tree planting, for example, one half could be reserved for natural regeneration.

Two famous examples of this are the Geescroft and Broadbalk wildernesses at the Rothamsted Experimental Station in Hertfordshire.  Here arable fields were abandoned in the 1880s and have long been regenerated woodlands.  There is an interesting comment about this in Footprints in the Soil (2006) edited by Benno Warkentin: These two historic Rothamsted sites illustrate the very considerable potential for carbon sequestration of simply allowing the steady state vegetation to re-establish itself.  Actively afforesting arable land will obviously be effective, but the more the soil is perturbed, the longer the benefit will take to materialize."

This weekend I was watching a tree planting day in Leicestershire on TV.  The small saplings were being planted in what was obviously stubble from a recent grain crop.  I did wonder, in these days of grain shortages, about the pros and cons of turning arable fields into woods.  And I also wondered about the transactional details of the arrangement.  There was no discussion of this on the TV programme.  Via some quick research I found out that arable land in Leicestershire is on offer at around £9,000 per acre ...  I assume a farmer would not want to arrange for extensive tree planting on arable sites unless there was some sort of financial return far beyond the scope of the kinds of grants offered by the government for farm management with wildlife in mind.

One final point, while many pests and diseases have been transported from their natural homes to somewhere else, I suspect that pathogens like ash dieback are often a natural phenomenon and that many plant species have gone through the kind of reversal now afflicting ash trees.  It just underlines that our human perspectives are often little longer than the average lifetime.

Sunday, November 18, 2012

Pigeons and plumes

From this time of year we always have two or three woodpigeons (Columba palumbus) eating the ivy berries on top of the hedge and in the tree behind.


Ivy berries contain toxins, but many birds seem able to cope with them.  Pigeons, however, eat the rather soft seed where the toxins are said to be concentrated, as well as the fruit pulp and can destroy over 75% of the ivy seed crop.  They start with the unripe berries at this time of year and continue to feed on them right through to spring when they are properly ripe.

A small mid-November treat today was the appearance of the beautiful plume moth (Amblyptilia acanthodactyla) on the wall by our back door.  This second generation emerges in autumn and goes into hibernation until spring, but this one quite evidently had not yet decided to settle down despite the fact that we have already had a couple of frosts.


The larvae feed on a variety of plants including hedge woundwort (Stachys sylvatica), of which we have a very large patch only a few metres from where I found the moth today.

The beautiful plume is one of those species that is increasing and these days is increasingly found in gardens, highlighting their value for some forms of wildlife.

Friday, November 16, 2012

Ash dieback in Poland and Japan

Two very interesting articles have been published recently on ash dieback disease (Chalara fraxinea).

One, in the Telegraph, is by Cole Moreton  who went to the forest area in Zabodny, Poland, where the disease was first noted in Europe in 1992:


It paints a very gloomy picture of the prospects for ash trees in the UK.  One of their forest managers was asked about prospects here:

“Has it been seen in the older trees?” It has. This experienced man of the forests puts his hand on his heart. “Then I am afraid it is over for you. It is too late. The game is over.”  However, the Poles pointed out that 15 to 20% of trees survive and seed from these might carry the immunity to future generations.

While this may seem to be a good thing, the warning from the Botanical Society of the British Isles (BSBI) should be heeded: "Woodland plantations and hedgerows made of cloned stock or non-native trees are going to be even more prone to failure than most food crops, as they are so long-lived."  In other words it is important to maintain genetic diversity and not take all future ash trees from one or two genetically identical, or very similar, clones."  The BSBI also say, rather more encouragingly: "Ash dieback, like other diseases of wild plants, is simply part of the ecosystem, and its main effect is likely to be to increase diversity and ultimately the stability of woods. Even if it were possible, there would be no point in trying to isolate British plants from worldwide diseases, because that would make them more vulnerable to serious plagues in future."

The whole article is here: http://www.bsbi.org.uk/ash_dieback.html

Their assertion though that "ash dieback is not known to kill mature trees" does not seem to be correct in the light of experience from Poland and elsewhere.

Another enlightening web site is TreeBASE (a database of phylogenetic knowledge) which almost certainly explains various reports that ash dieback came from Asia or China.  In fact the fungus seems to be present in Japan on Manchurian ash (Fraxinus mandshurica) a species found in China, Korea and south east Russia as well as Japan.  TreeBASE say: "Hymenoscyphus pseudoalbidus is the causal agent of ash (Fraxinus excelsior) dieback in Europe. It was recently separated from the European H. albidus based on molecular analyses, while morphologically scarcely distinguishable. Hymenoscyphus albidus was reported under the nomenclatural synonym Lambertella albida on petioles of Fraxinus mandshurica in Japan."  It then gives some rather more complicated details.


On the assumption that the fungus was present in Japan before Europe, Manchurian ash may, of course, be rather more resistant to the disease than European ash, but much more work needs to be done to establish the evolutionary pathways and possible dispersion routes of spores of both the European and Far Eastern strains of Chalara fraxinea, although such knowledge may not enable anyone to stop its advance, it could help with mitigation strategies.

Work on Chalara fraxinea seems to have been done by scientists in Japan, Poland, Denmark, Belgium, Switzerland, UK and probably many other places.  What I find rather disturbing is that they do not appear to be talking to one another and reading one another's papers.  Or maybe they are simply being ignored.

Thursday, November 15, 2012

Ash dieback again

Below: a healthy (for how long?) coppiced ash.


Many people in the media still seem to be behind the times on ash dieback and continue to prattle on about Denmark and how the disease is widespread in Central Europe (home of Count Dracula etc.)

Chalara fraxinea had spread to north west France by 2009 and Belgium since at least 2010. For more detail see: http://tinyurl.com/d6soy9s

The Forestry Commission map of Chalara outbreaks ignores the very significant fact that the disease is widespread in the bit of France shown bottom left just opposite the Kent outbreaks See: http://tinyurl.com/d4qp7t5

Surely it is pointless to 'take action' of whatever kind here when spores will keep arriving from Europe unless the disease declines of its own accord. I continue to read of hundreds of people scouring the countryside for infected trees, but it is not quite clear what they do when they find them. Do they destroy the whole thing, roots and all, and hoover the entire woodland floor or length of hedge for any spore carrying leaves?

Are these hundreds of people volunteers, long-term employees of someone, or recent recruits? Have they stopped doing their proper job? Whenever hundreds are involved there is usually a significant cost. Is it worth it?

Another piece of data that seems to have lain undiscovered is that ash dieback was added to the European and Mediterranean Plant Protection Organisation's (EPPO) alert list in 2007. They said: "Because ash dieback could represent a serious threat to forest, amenity and nursery ash trees, the EPPO Secretariat decided to add C. fraxinea to the EPPO Alert List in 2007." The UK has been a member of EPPO since 1951 but seemingly ignored this warning.  See: http://tinyurl.com/catk78n

I think I am suffering with Roper dieback.