Please note that the conclusion refers to a piece of bark 4.54mm wide and 3.24mm thick (25,4mm = 1 inch).
Several bows were examined and only one possibly had a bark facing.
Sinew coatings, sinew and bark wrappings had several bows
The whole thing can be perceived as an interesting detail but nothing more.
That's what's left. It was clearly stated that the belly strip of tree bark was structural.
"To this we should add that the fruit-tree plate glued to the belly also contributed to the stiffness of the bow. this combination of various flexible and resilient materials in the design of the bow from Vodoslavka kurgan allowed the bow with short shoulders to impart more energy to the arrow than a simple bow construction."
The tree bark was not a mere decoration or water-proofing. It was used as a part of pre-stressing the two layer limbs. A simple experimentation is in order.
Can someone glue a 1" wide, 1/2" thick and 24" long hickory strip to a 1" wide, 1/4" thick, and 24" long cedar strip, pre-stressing them with 2 inch setback/reflex? Then we can compare its strength with a same size, 3/4" thick, hickory stave. It can be heat-bent to the same shape. I am not sure how long it will take for me to get around to do this myself. Thanks.