Tariff Table volume measurement of trees
Images are courtesy of Colin Lawson son of Wilfred Lawson, a forester who trained at Benmore Forester Training School and was posted to South Strome Forest from 1951.
Part of a form which records the numbers and measurements of trees which have been marked for felling in Ardnarff Section of South Strome Forest. Commonly called a Tariff Sheet or Form it is here annotated as Form S11and very similar to the Tariff Sheets used currently. The purpose of the form was to arrive at a total volume estimate for all the trees marked for felling in a defined area or compartment. This was easier said than done and involved following very closely a set of measuring rules as written out in a Forest Mensuration Handbook (Forestry Commission Booklet No 39) – in Procedure No 8.
A simple example is a stand of trees of one species, one age, fairly even sized in which a standard marking will been done for thinning and the expected total number marked for felling is around 2100 trees.
A booker will accompany two or even three markers as they cruise through the stand selecting and marking the trees with paint or axe which are to come out. Each time the axe or paint hits a tree the marker shouts ‘mark’ and the booker has to enter this via the gate method (four vertical strokes and one diagonal stroke over the four) into the boxed off page of the tariff sheet. At every tenth tree called, the booker calls ‘measure’ and the marker stops and measures the tree by placing a girthing tape around the circumference at a height of 1.3 meters above ground level known as breast height. This tape converts the circumference into a diameter reading (diameter breast height - dbh) and this figure is shouted back to the booker who records it against the appropriate diameter on the Trees Girthed page in the gate method again. The Trees Girthed page had a list of all the diameter classes from 7cm through to 40 cm and higher if required with rows against each for recording the gate marks.
This process carries on as described until a marker shouts ‘mark’ which happens to be a girthing measure tree but also the 10th such tree (or the 100th marked in total) at which the booker calls ‘sample tree’. The girth is entered into the girthing table and also into the Sample Tree page against the next number in sequence (1 if it is the first sample tree -2 if it is the second etc). This number is called back to the marker who paints it on the tree and marks the point at which the dbh was taken. Before the advent of spray paint the numbers and dbh point were gouged into the bark of the tree with a special tool called a timber scribe which had a gouge hooked blade for the purpose. Marking and booking commenced as above until the whole stand was marked.
At some point the sample trees were felled and their length and diameters at the midpoint measured, all of which was entered against the appropriate tree number in the Sample Tree page. Leaving this job to the end often entailed quite a search to find the sample tree locations again and this is where the spray paint helped greatly. Very often a section was marked and then the team retraced their steps carrying saws, pulling winches and long tapes while locations were fresh in the memory.
Once all measurement details were complete, the form was taken to the forest office and the calculations worked out from various tables. The aim was arrive at an average Tariff Number for the stand (the taller the tree for a given diameter at breast height the higher the tariff number) and use this average number to calculate all the volumes for the total numbers of trees marked in each diameter breast height class.
After all this work the estimated volume figure, if the procedure was adhered to precisely, was said to be within 10% of the actual outturn volume once all the felling was done. The PDF shows a worked example from Booklet No 39.
Perhaps someone will come up with stories of ‘shortcuts’ and replacing ‘lost’ sample volume trees which happened all too easily in thick unbrashed Sitka spruce.
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Groups: Forestry Areas, Forestry Records, Booklets and Reports