Regular readers will be familiar with the idea that a tree stump can be used as a compass.
In trees exposed to plenty of sun, the heart is more commonly found on the south side. If there are strong prevailing winds, there is also a trend for it to appear on the side those winds come from, the southwest side in the UK and NW Europe.
But there is an aspect to this that I have been trying to refine for a few months.
Sadly, thousands of ash trees are being felled because of ash dieback (Hymenoscyphus fraxineus).
On a cheerier note, there are now so many freshly sawn tree stumps on the hills near me that it offered a golden opportunity.
I decided to focus on one trend that I had spotted from time to time, but never really nailed down. In truth, it’s something I’ve been meaning to investigate for years.
I looked at lots of examples of tree stumps on a hill that rose up to the south. This allowed me to answer a simple question:
Hill gradient influences the shape of tree’s guy roots, but does this change the shape of the trunk enough to influence the position of the heart of the tree?
After studying many of these stumps, the answer is clear: yes.
There are slightly different patterns for conifers, but here I’ll focus on deciduous trees.
A hill gradient leads to a much more substantial guy root on the downhill side of the tree. This changes the shape of the trunk and the position of the heart.
On any steep hill, the heart of the tree is more likely to appear on the downhill side of the trunk, regardless of aspect.
In the picture at the top, we would expect the heart to be nearer the top edge if this tree was on flat ground, as that is the southern edge. But it’s on a steep slope and this dominates.
It follows that we need to care using tree stumps as a compass whenever there is a gradient.
Incidentally, where I did find evidence of ash dieback in the trunks, it was almost always as a V shape on the southern / uphill side.
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