Knocked off balance

Locally wide tree rings

These five wide tree rings on one side of the stem indicate a tilted position, having been slightly knocked over because of a landslide or a storm.

A tilted conifer compensates for the weight shift with the formation of compression wood on the underside of the trunk. Compression wood is darker than normal wood because it consists of cells with thickened walls. It also characteristically consists of clearly rounded cells.

Bouncing cellulose fibres

Longitudinal section through compression wood cells. In a compression wood cell, cellulose fibres (microfibrils) build up the cell walls like a spiral. The microfibrils (green arrows) act like bouncing springs. As the cells turn into wood (= lignification), lignin is stored between fibrils. This forces the spirals apart and makes the cells longer. The resulting pressure straightens the tree bit by bit.

The tips of microfibril spirals (green arrows) are visible in this cross-section of compression wood cells.

Vajonte 1963: torn along with the landslide

This disc was taken from a larch that was dragged downhill with the giant Vajont dam landslide (Italy) on October 9, 1963 but continued to grow in the valley with a large tilt.

After the catastrophe, the tree showed very strong growth of compression wood on the underside of the trunk, while the growth on the upper side was dramatically reduced (= eccentric annual rings).

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Knocked off balance