Cracks  - There are two basic types of cracks.  Cracks that start from wounds on the inside that work their way to the surface. The other are shallow cracks that start from the outside in.  Cracks form first and then microorganisms follow the cracks.  Cracks that start from the outer bark inward are usually very shallow. 

Picture at left.  Long shallow crack
Image Source - TREES, ASSOCIATES, and SHIGO (2 CD set).

Large internal cracks start from weakened spots such as wounds, branch stubs, dead spots between co-dominant stems or roots, and insect wounds. Cracks will never be understood from the transverse plane only.  Longitudinal radial dissection must be made not only to understand cracks but other internal defects.  Click here for some pictures of cracks.  Trees with extensive hollows are at high risk for fracture during moderate to high winds.  Cracks usually are more prone to fracturing than hollows. (See TREE PITHY POINTS, SHIGO, 1999 pg 113)  Trees play games in the wind.  Sometimes they get rough!

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