Thetford silver birch provenance trial (Part 1)

For my Honours dissertation, I am assessing variation within and between two silver birch provenance trials; one in Thetford, Nofolk, England, and the other at Drummond Hill near Loch Tay, Scotland. For an excellent explanation of what these trials are all about, see this page by BIHIP (British and Irish Hardwoods Improvement Programme), the people who set up the trials. Provenance is essentially the area of seed origin, so for example birches of provenance 'Eastern Moors, Sheffield' are from seed collected from Eastern Moors, Sheffield. Different provenances vary in attributes such as growth rate. Essentially, the provenance trials aim to determine which provenances are most suitable for timber production.

For my dissertation I am collecting data on 32 different silver birch provenances from England, Scotland, Wales, Denmark and Norway (plus 8 from France) at two trials, Thetford 312 and Drummond 34. I will then assess variation between provenances within each trial and within each provenance between the two trials. Each trial contains three 'blocks', and each block contains square plots of 25 trees for every provenance; thus each provenance is represented by 75 trees at each trial. This replication helps ensure a fair trial. My data collection involves assessing the following attributes: height; girth at breast height; number of main stems; and number of bends in main stems. I am sampling the middle 9 trees of each plot of the 32 provenances I am interested in, which means I will be sampling a total of (9 x 3 x 32) 864 trees (plus some French ones that I am doing separate because they were planted later).

Trees best suited for timber production will be fast growing (tall and large girthed) with a single straight stem. You can't get a good, long piece of wood out of a tree that is bending all over the place!

Anyway, I have now collected all the data I need from the Thetford trial, with my father acting as my assistant. It took us three and a half days, starting on Wednesday the 27th of Feburary and finishing on Saturday the 1st of March. Now I just need to get up to the Highlands and do it all again at Drummond Hill!

thetford silver birch provenance trial

A typical view of Thetford 312 silver birch provenance trial. Look how neat and perfect it all is! I did some smaller scale data collection at the Scottish Kintyre 20 silver birch provenance trial in September 2007 and it was an overgrown pain in the ass, the complete opposite of the Thetford trial.

estimating height with a measuring stick

My paternal assistant with our homemade, 5.6 metre long measuring stick. Each coloured band is 20 centimetres. He would stand with the stick next to the sample tree, and I would stand back to make a good estimate of height to the nearest 10 centimetres. The sample tree in this photo is the champion for height - just over 8 metres tall I believe.

a fighter jet over the trial

The trial is very close to Feltwell Royal Air Force Base so we got fighter jets roaring through the sky all day. At five o'clock they would play music though loudspeakers and on Wednesday it was Reveille.

identification tag

Wooden poles with an identification tag are found at one corner of each plot. Not sure what 'EDC 19' means. I believe 'B 101' is a typo - it should read 'BI 01' which stands for birch, seed collected in 2001. In 'RPN 404', the RP stands for 'region of provenance' and the N probably stands for 'native seed-zone'. This awesome map on the BIHIP site shows regions of provenance and native seed-zones. The tag in my photo is for provenance 'Rushmore Estate, Tollard Royal', just in case you were wondering!

measuring girth

Girth at breast height (about 1.6 metres) was measured to the nearest 5 millimetres with a tape measure. This data will be converted into diameter at breast height (DBH). The tree in this photo doesn't really have a girth in the 40s - the tape measure was cut to begin at 30 centimetres because the first day of intense girth-measuring had worn all the lower numbers off!

the edge of the trial

The edge of the trial. The trial was surrounded on all sides by Scots pine plantations of various age. In this photo one such plantation is on the far left, then moving right there is a forest road, a fence to keep out grazers (which had failed to keep out rabbits), young Scots pine invaders from seed blown in, and furthest right a buffer strip two silver birches wide before the actual trial trees begin.

Now read Thetford silver birch provenance trial (Part 2) !


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