From Pathfinder Treasure Vault (Remastered), which isn't enabled.

Sapling Shield (Major)

ITEM 15

MAGICAL

Price 5860 gp

Bulk 2

AC Bonus +1

Hardness 13

HP 104

BT 52

This surprisingly weighty, though well-balanced, wooden buckler (Hardness 13, HP 104, and BT 52) is emblazoned with the image of a sapling. The sapling withers as the shield takes damage.

Activate (concentrate)

Effect The buckler expands, with the sapling image growing into a mighty oak tree. The buckler becomes a tower shield, gaining the corresponding AC bonus, Speed penalty, and ability to Take Cover. It keeps the same Hit Points and Broken Threshold, but its Hardness and Bulk increase by 2 in this form. The shield remains in this form until you Activate it again to revert it to a buckler.

Pathfinder Treasure Vault (Remastered)ORC