These notes were made quite recently by a doctor from The University of Aberdeen and Simon Lenihan, of Celtic Horse Logging.The doctor has long been concerned about the effects of machine logging in Scotland and it's impact on The Forests, Rivers, and Loch's. After seeing Simon's team at work in Scotland, they made a sample study of a nearby plantation block. The logging team would consist of 3 men, two horses, whilst the machine team would probably be along the lines of a small thinning harvester, forwarder 3-4 tonne capacity.
Comparison of mechanised logging with horse logging
Example a 100-acre Scots pine plantation, 45 years old and unthinned, average tree size = 0.25 cubic metres, stocking density 800 trees/acre, so 200 cubic metres/acre, and value of one acre is £6,000.This is based on 1 cubic metre with a roadside value of £30 felled and extracted to roadside ready for collection.
A useful method to find the average size of trees in a plot is as follows. The size in cubic metres per tree and the use of such timber are
0.1 deadwood, chipwood and fencing material
0.2 chipwood and fencing material
0.3 chipwood and small saw logs (final crop)
0.4 chipwood and large saw logs (final crop)
The average tree in this case is 0.25, equivalent to 4 trees per cubic metre and 200 tonnes per acre at a stocking density of 800 trees/acre.
Now imagine that you cut all of the 800 trees. You then allocate them to the specifications required by sawmills. All twisted and dead trees go for chipwood and amount to 33%, all small straight timber is used for fencing material and amounting to 33%, and all saw logs amount to 33%. Note that when you remove 25% of all the small-diameter trees, you do not remove all the crooked ones, because some trees have the bottom section of the tree straight though the tops are twisted. Using the above three categories at 33% each, the poorest 33% of the standing timber has a value of £20/cubic metre at the roadside ready for collection. The middle 33% of the standing timber has a value of £30/cubic metre at the roadside, and the top 33% of the standing timber a value of £40/cubic metre at the roadside.
Thinning by motor manual felling and horse extraction, on a sample plot of one acre, would involve a complete selection thinning, removing the poorest trees. These would be all trees of 0.1 cubic metre, resulting in a volume to be thinned of 25% or 200 trees. A 25% thinning that removed all trees of 0.1 cubic metres each would produce chipwood and fencing material at about 50:50 each. For 10 cubic metres of chipwood the timber sale yields £200 and for 10 cubic metres of fencing material the sale is £300, so the total income from timber sales on one acre is £500.
The value of the timber stand on one acre prior to thinning is £6,000. Thinning removes 200 trees at 0.1, which increases the average dbh (diameter at breast height) from 0.25 of a cubic metre to 0.30. Because the value per cubic metre is now £35, the value of this one-acre stand has risen to £6,300. The cost of harvesting 200 trees at 0.1 or 20 cubic metres, using horses, involves two days' work at £500/day, totalling £1,000. The income to the landowner from timber sales is £500, so the short-term loss to the owner is £500, but the stand has increased in value by £300.
Also, with a growth rate of 10 cm dbh over 5 years, this would increase the average tree size by 0.2, bringing it up to 0.5 cubic metres. Moreover, the value of the one-acre stand has now risen to £9,000. This is an increase of £3,000/acre, and in a 100-acre stand the corresponding increase would be £300,000. This would be the final thin, and would leave a valuable crop that has been selectively thinned and that will be more likely to withstand the elements. Horse extraction causes no damage to soils, watercourses and the remaining standing trees. It is the only sustainable method of tree harvesting, and this sustainable method is powered mainly by hay and grain produced by our solar system.
Mechanised logging takes 25% of the timber in the first “thinning”, which in fact is not thinning but clear-felling along a double linear row. The machine will have to take a double row for access into the above example of a very densely planted wood (this would not apply on a less densely planted wood). Whether the machine takes a single or double row, it will end up taking the average tree of 0.25 cubic metres throughout the stand Over two days the machine removes 200 trees at 0.25, which equates to 50 cubic metres at £30/cubic metre. The income to the contractor is £1,000, and to the owner £500. The value of the one-acre stand prior to machine thinning is £6,000, the value afterwards being £4,500. This equates to a gross loss to the owner of £1,500, and a net loss of £1,000 if one allows for the income of £500.
For the sake of argument, let us assume that the machine causes no damage to ground and to the remaining standing trees (an assumption clearly at variance with the facts, as anyone can see on the ground), and hence that there are no side-effect costs. Given a tree growth rate of 10 cm dbh over 5 years as above, this would bring the timber stand up to 0.45 cubic metre/tree. It would take over 30 months of growth for the sample one-acre plot to be worth £6,000 again.
If the machine takes out 4 racks, this would equate to almost 25%. That would leave many of the smaller-diameter trees remaining, when in sound traditional silviculture they ought to be removed so as to aid better growth from the finer specimen Scots pines that are left uncut.
