Highgate Wood Heritage Day

2014-08-27 15:18

Twig pencils

Twig pencils at the ready for Highgate Wood Heritage Day

With a bit of luck I’ll actually be making some charcoal there, too.

Iain Loasby




North London Charcoal once again

2014-07-12 14:11

… eventually.

It was hoped that the 1st-4th August would have seen Queen’s Wood in Haringey becoming a site of charcoal production again for perhaps the first time in living memory.

Unfortunately, I’ve not been able to find an additional qualified First Aider able to spend the night with me and the retort in the wood in time, so it’ll be a bit longer before charcoal returns to Queen’s Wood.

I will be there for the Family Fun Day on Saturday with the retort on display, but no charring action this time.

Iain Loasby



National Coppice Federation

2013-04-30 07:34

This last weekend I took a trip to Malvern in Worcestershire for the inaugural AGM of the fledgling National Coppice Federation.

There were guest speakers, demonstrations of crafts and useful ideas, some nice visits to other peoples’ woods to see how they work, and, of course, some cider and some venison sausages sat around a fire pit. The main business of the occasion was to agree the articles and elect the directors of NCFed.

This is not the first attempt to form a national body to represent coppice workers, with previous efforts in the 90s appearing to peter out for one reason or another, though a number of regional groups emerged to fill some of the needs.

It seems as though there could be some major benefits to having a national association, not least a single entity to represent coppice workers generally – who spoke for coppice on the Independent Panel on Forestry

There are, however, some obstacles to overcome.

“Coppicing” as a term covers a pretty broad range of operations: from near-industrial chestnut coppice making paling by the mile; individual craftsmen; firewood production; charcoal production; old boys who’ve been at it all their lives working the same woods their parents did before them; “upstarts” (like myself) trying to return the remnants of their local coppice to a viable productive state; “conservation coppice” trying to maintain the legacy of wildlife benefits that millennia of coppicing has left us and pretty much every shade of variation in-between. Bringing all this together into a coherent organisation seems like a pretty major challenge in itself.

Then there are the coppice workers themselves and the scars and the baggage and the politics that remain from previous attempts. There seems to be a widespread perception that a national association will be just a talking shop run by paper pushers with little practical use for “the doers” out there working in the woods. If those “doers” don’t make an effort to get involved and influence the way the organisation progresses then that will be a self-fulfilling prophecy.

I’ve had the pleasure of meeting several of the people who now form the “directors” of the National Coppice Federation and I’ll trust them to make a decent fist of pulling something useful together.

I don’t think coppice workers – of whatever variety – should leave them to do it on their own.

Iain Loasby




Why do trees die?

2013-02-17 23:20

Not because of coppicing, that’s for sure (not native broadleaved trees with proper consideration to their needs, anyway – there’s always a qualifier where trees are concerned; always an exception)! Coppicing can actually extend a trees natural lifespan almost indefinitely.

There are many external factors that can speed or bring about the end of a tree’s life: competition for resources, pests and diseases, pollution, root damage and mechanical injury to name just a few. Yet, even without these outside influences, trees have a natural limit to their lifespan and will eventually grow old and die.

In order to grow quickly the Silver Birch (Betula pendula) makes much less of an investment in strength and longevity than the slower growing Oaks (Quercus spp.). A birch tree could never reach the same ultimate size as an oak tree as it simply would not be able to hold up the weight of it’s own branches.

The ability to support branches – and, thus, it’s food producing leaves – is a major factor in a tree’s longevity.

Trees (woody perennials) grow by adding a complete new sheath of wood around themselves each year. As the tree grows ever larger, so does the surface area which it needs to cover with new wood and, eventually, the cost of producing this new layer begins to outweigh the amount of food produced by the leaves the tree can hold up.

As the cost of producing a new covering of wood increases, a tree will tend to produce thinner and thinner layers of new wood. Because it is this new wood which transports water around the tree this results in a shortage of water in the upper branches which then begin to die off. This process produces the common sight of “stag-headed” oaks (other species of tree take this approach, but the strength and durability of oak means that even the dead branches may persist for decades or more making them much more obvious).

In an oak this period of retrenchment may last 100s of years but, with less and less ability to produce food and more and more surface area to cover, a downward spiral has begun. Even with the best of conditions there comes a point where there is no more net gain to be had from giving up food production to limit the amount new wood needed and the tree will have finally reached the end of its life.

By coppicing a tree this process is effectively reset – again and again! Tree roots grow in the same way as the branches, so there is a theoretical limit, but coppicing can allow trees which might normally live for hundreds of years to reach thousands of years of age.

If you want to find out more about the fascinating ways trees live (and die) I can recommend no book more than Trees: Their Natural History by Peter Thomas.

Iain Loasby




Why does Chestnut spit?

2012-09-29 19:17

Unsurprisingly, we have a wood burning stove. As the evenings have grown a little cool and damp, we’ve had it on a bit this week. Even without the stove, I’ve certainly sat round enough camp fires to know that certain woods spit more than others.

There’s plenty of lore and wisdom on the internet about firewood: “This wood’s good; that wood’s bad; this wood spits more than that wood”, but none of them tell me why Sweet Chustnut (Castanea sativa) spits so much.

Oak shingles on a roof

I’ve thought it might be to do with the structure of the wood. Some hardwoods contain tyloses and softwoods have a mechanism for damming up their tracheids to block the water-carrying xylem cells when wood is damaged, perhaps creating an enclosed space that will burst open when heated, but these features are common to many woods.

If it was to do with the ease of splitting the wood, allowing the forces to burst the log apart more easily, it might explain why small offcuts from Oak shingles spit so much more than a solid log, but not why Ash spits any less than Chestnut.

I’ve read that wood spits because it’s too green, but also that “Plane” "burns pleasantly, but is apt to throw sparks if very dry"
and it’s pretty plain that seasoned chestnut spits more than many unseasoned woods.

Burning green wood (yes, even Ash) is bad because it contains more water, so the heat from the fire goes to driving off the moisture before the wood can burn; the wood burns less efficiently, produces more smoke and provides less heat for your house. But why doesn’t water burn? Turns out water is "already ash", the result of hydrogen combusting. News to me!

I’ve found a page that says
there might be the occasional spit or spark due to small insects under the bark, which is an entertaining idea (perhaps not for the insect), but then also says that softwood spits and hardwood doesn’t and that Hazel is a softwood, so I don’t think we’ll put too much stock in that!

Burning jet of gas inside an Exeter Retort

David Blake suggests that softwoods spit because of the resins they contain. This is a pretty compelling argument as resin is composed of volatile hydrocarbons and can burn quite spectacularly, but I wouldn’t have thought of Chestnut as particularly resinous.

Like all wood, Chestnut does contain hydrocarbons. It is the volatile hydrocarbons, converted to gas, that give the dancing flame above a fire. These volatile compounds are driven off when making charcoal (which is why charcoal burns without a flame) and, when using a retort, you can see spikes in temperature as different gases come “on stream” at different times.

So there’s a few clues, but I’m not really any closer to a definitive answer. Perhaps the answer lies in a combination of them all. Whatever the answer, it’s keeping my toes warm!

Iain Loasby




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