Fire down below

Fire is a major driver of forest dynamics and helps determine the structure and composition of continental forests of pine and spruce.  Evidence that natural fires were an important factor in the history of the Scottish native pinewoods is more limited: in our Atlantic climate, the chances of lightning setting off a fire without it then being dampened down by rain are more remote.  However controlled burns have often been suggested as a way of reducing the ground vegetation and dense litter layer, to allow more opportunities for pine regeneration.

NH4689 15_8 Amat pinewood closed grown tree.JPGNO4693 86_6 Glen Tanar pine seedling in burnt area.jpg

Further south Oliver Rackham noted that British broadleaved woods burn like wet asbestos, and hence the idea that our ancestors used fire extensively to clear the wildwood should be treated with caution. However, fires can spread through broadleaved woodland, where the canopy is relatively open with much dry grass or bracken. So, there used to be occasion reports in the West Essex Gazette of fires in Epping Forest. Similarly, a number of the veteran trees on Ashsted Common were killed by a fire there.

fire area with hulks 5.JPG

 At Sheephouse Wood I once came across a little line of smouldering leaves. The main burning of lop and top had been put out, but sparks had got into a rut in the ride where the litter had accumulated and the fire was slowly working its way along it.  A few years earlier part of a newly planted area which had become dominated by tall tufted hair-grass and wood small-reed burnt, probably from a similar cause, plastic spiral guards and Tuley tubes adding to damage to the young trees. SP7023 91_8 fire area 84fell b

Part of Wytham Woods also burnt, not once, but twice, in both cases spreading up the slope from the field below where someone had been careless with their matches, pipe ash etc. Both times were late spring when tall dry grass and bracken are particular flammable.  Fire scars are still visible on the up-slope side of some of the oaks (even though the fire was burning up the hill) because as Oliver pointed out when he visited, that is where the most leaf litter is.the young trees.

Extract from Charles Elton’s diaries for Wytham Woods.

 9/4/56  In the early afternoon Soper, of the University’s Experimental Farm, accidentally dropped a lighted match on the towpath just by Clap Gate in Wytham Mead, inside the rough patch left as a “reserve”. The fire caught the grass, which in the south of England is as dry as tinder this spring, and got into the Wood before he could stop it. A strong west wind drove it into Hither Clay Hill, all except the outer fringe of which was burned to the ground (though the scattered trees, mainly oaks, which caught fire, may have been only partially hurt) – much thick scrub and the bracken areas. It was fought by the Fire Brigade and the foresters etc., and Soper for some hours, and just checked along the line of Lower Ride. Southern and Lowe have made a detailed map of the burn. The trap grid has some 10 acres burned off, and the Reserve as a whole has had some 20-30 acres go. The total area is about 30 acres. It did not reach Varley’s oak acre. The eventual effect may however be partially beneficial, as the area has become over-solid with thorn scrub and bracken.

Fire in plantations was a major problem for the Forestry Commission in its early years, particularly in some of its forests in the south Wales coalfields. More recently (2011) there was a major fire in Swinley Forest near Windsor. This was particularly bad because at times it got into the canopy, dead lower branches in young stands can provide a fire ladder. The areas worst affected have been cleared and restocked and the eventual outcome may be that the structure of the forest becomes more varied. Some areas around mire pools have been left unplanted to add to the open space.  Blackening on lower trunks of some of the trees left is an indication of how extensive the fire and its effects were, but also an indication of the robustness of some trees in the face of this disturbance.

17_4 SU8564 Crowthorne area blackened base 5 17_4 SU8564 Crowthorne area blackened bases and regen 3

What was also very impressive was the extent of pine and also birch regeneration that was taking place. The main ground flora species – bracken, bilberry, heather, with purple moor-grass in the wetter areas – had also come back well.

One of the possible consequences of climate change, particularly in south-east England is that risk of forest fires increases, not necessarily because natural fires start more often – humans are likely to remain the main cause of ignition – but because the vegetation is dryer and more vulnerable.  Experiences from Swinley and the other sites may help us to cope with these changes.

 

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