Frog coin tree, Pressmennan Wood, East Lothian

We're a superstitious lot, but I don't know when the practice of hammering coins into trees, such as this carved tree stump began? Does anyone have any ideas? This example and many others can be seen in Pressmennan Wood, East Lothian, Scotland. More details here: https://www.woodlandtrust.org.uk/visiting-woods/wood/?woodId=4908&woodName=pressmennan-wood Model produced from 93 images taken on a Samsung S8. Source: Objaverse 1.0 / Sketchfab