Inonotus obliquus, also known as ”sprängticka” here in Sweden, is an interesting fungus. I’ve only seen it in Sweden and only on Birch (Betula spp.). Recently I’ve been comparing the actual decay caused by the fungus with the readings from my Rinntech Arbotom tomograph.
The fungus decays wood in the area of the sterile ”fruit” body as well as causing a canker at the site of infection, so that new wood and bark cannot form there. The type of decay does not appear to have been studied in detail, but associated fractures are brittle in nature.
There appears to be some debate about the fungus’ pathology. The fungus might enter the tree through a wound and then eat a path towards the tree’s centre, or it may be endemic and develop from the centre out towards a suitable exit point for the fruiting body.
Once established, it certainly appears that the fungus spreads longitudinally with relative ease. The fungus is associated with stem failure at the site of the canker.
Here is a comparison of a tomograph with the severed stem of a mature Betula pendula with Inonotus obliquus:
As you can see, the tomograph illustrates the decay with good accuracy. There is decay in the area where the fruiting body exits the stem (between sensors 4 and 5), as well as in the centre of the tree.
Below is another birch with Inonotus obliquus in the stem, with the resulting tomograph and severed stem:
Again in this example, the tomograph reflects well the decay in the tree’s centre and at the exit point to the stem (the photo of the cross-section doesn’t quite line up with the tomograph). In addition, the tomograph also appears to show dysfunction in the wood between sensors 3 and 4. There was no apparent decay here in the actual wood, but in the lowest photograph staining can be seen in the areas of sensors 3 and 4, which might be the beginning of dysfunction.
This second tree could probably have been retained for a few years – the quantity of load-bearing wood appeared sufficient – however, given its location in pre-school grounds and the resources involved in on-going surveillance, the decision to remove the tree was expedient.
And finally, a photograph and tomograph of a Birch with Inonotus obliquus that we have decided to retain and monitor via tomography over the coming years:
- Progressive Stages of Discoloration and Decay Associated with the Canker-Rot Fungus, Inonotus obliquus, in Birch. Robert A. Blanchette, Assistant professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108; Phytopathology 72:1272-1277. (pdf download available at https://www.apsnet.org/publications/phytopathology/backissues/Documents/1982Abstracts/Phyto72_1272.htm Page accessed 27 march 2017)
Lonsdale, D. (1999). Principles of tree hazard assessment and management. Forestry Commission Research for Amenity Trees No. 7. Norwich, Storbritannien: The Stationery Office.