Macro-scale stresses on bark cause patterning

Many types of stresses occur on bark due to development and growth. These lead to the patterns you see on the bark of tree trunks. 

Micro-scale (meristematic) processes lead to macro-scale bark patterns

These meristematic growth patterns are hypothesized to result in the macro-scale bark patterns we observe in trees. 

Historical repeat photography can be used to test bark patterning hypotheses

Here two photographs taken at 79 year interval were used to show how bark patterns changed over time. 

Note the Eastman image is from:

Eastman, Jervie Henry. 1941. “Butte Lake.” Eastman’s Originals Collection. University of California, Davis. General Library. Dept. of Special Collections. 1941. https://digital.ucdavis.edu/collection/eastman/D-051/T-1/T-1350.