Why Does a Grape Cane Shred Its Bark

When we are walking in the vineyard, my husband and I often come across vines that are sloughing off their outer bark in shreds. We wondered if this was good or bad. I thought it was okay because somewhere I read that the sloughing off of the outer bark is a sign of older wood. I did some online research and came across the answer and followed it into the rabbit hole as I searched for more information.
While reading the online literature on the periderm, I came across words such as phellogen, phellem and phelloderm and things became a bit confusing. I understand best when I can see a diagram so I searched the Internet and the offerings were few until I came across Theoretical Aspects of Vascular Anatomy with all the illustrations that I could possibly wish for! Take a look at this beautiful illustration of the cross section of a grape shoot:¹

The vascular cambium, also simply called cambium is where all the action takes place. The cambium consists of a single layer of cells which produces xylem cells to the inside and phloem cells to the outside. Every year, the cambium produces new phloem and xylem and adds to the girth the grape cane.
Once a year, some cells in the outer layer of the phloem becomes meristematic and regains the ability to produce new cells and growth. This meristematic growth produces the cork cambium which in turn produces a layer of new cork cells that becomes impregnated with a waxy substance cutting off the water supply to the cork cells and older phloem.

Cork cells die after they reach full size and then they become impervious to water. When fully formed, the periderm or what we know as the bark seals off the inner dehydrating cells from the once green outer cortex, which then dies and turns brown.
This periderm is made up of the:

• Cork cambium/(phellogen)
• Cork/phellem is produced towards the outside
• "Cork-skin"/phelloderm is produced on the inside

Each year, new meristematic growth that produces the cork cambium (phellogen) adds to the accumulated periderm of previous years and this accumulation is what causes the bark to slough off!
References:
1. Theoretical Aspects of Vascular Anatomy
2. Tim Martinson, Assessing Winter Cold Injury of Grape Canes and Trunks, Cornell University, 2011.
3. Edward W. Hellman, Grapevine Structure and Function.
4. Michael G. Mullins, ‎Alain Bouquet, ‎Larry E. Williams, Biology of the Grapevine, pg. 53.