Any explanations why a tree would split like this?

[Arctostaphylos uva-ursi]

Janey,

This type of splitting (shear cracks) of a trunk not only can originate from twisting (torsion forces) of a tree "under full sails" or foliage by (rain and) storm winds alone, but sometimes can be predetermined and caused by the mycelium of Ganoderma australe decomposing the central core of the heart wood of oaks (see photo).

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Hmn. Not sure what you mean by predetermined here? Is it not exacerbated by rather than predetermined? Please expand.

[Arctostaphylos uva-ursi]

I assume you mean that the fungus assists in delamination by the breakdown of lignin and the already weakened tissue is then pulled appart by forces acting on the crown? So its a case of fungal action first followed by mechanical/abiotic action rather than the other way round?

Edited June 27, 2011 by Arctostaphylos uva-ursi

[Fungus]

I assume you mean that the fungus assists in delamination by the breakdown of lignin and the already weakened tissue is then pulled appart by forces acting on the crown? So its a case of fungal action first followed by mechanical/abiotic action rather than the other way round?

 

Correct : Ganoderma species are white rotters with selective delignification changing the cellulose/lignin dependend flexibility/stiffness ratio of the heart wood of the tree, which makes the trunk vulnerable for splitting or delamination if it is twisted (torsion forces) "under full sails" (foliage) during a storm.

[Tony Croft aka hamadryad]

not just torsion, shear too.

[Fungus]

not just torsion, shear too.

 

Of course .

[Arctostaphylos uva-ursi]

Ok. Thanks for confirming.