In the UK there was an old tradition of thrashing the trunk with stiff canes/rods to bruise the bark and stimulate sap in the cambion layer to increase nut production. Can only guess damaging the tree like this fooled nature into thinking it was in trouble so produced fruit as a means of survival.
That's super interesting. There's a similar effect with a lot of fruit trees where if you cleanly cut the small branches with shears they will produce more small branches but if you twist them off they produce more fruit. The theory is that the clean shears make the tree think there are browsers so it needs more grow to deal with that.. whereas the twisting/breaking is more like something reaching around for fruit and accidentally breaking branches so more fruit.
The trunk bruising would be similar to a large animal reaching around the tree trying to get into the nuts maybe...
Found an article from
Pacific Rural Press, Volume 33, Number 26, 25 June 1887
"Editors Prkss:—l see a notice from Coloma, in El Dorado county, in your number of May 21st, asking " Why do walnuts drop?" and wishing a remedy for the evil.
I have some thrifty walnut trees at my country seat in Temescal, and they put it in their lofty heads to drop their fruit every year when the size of a marble, as your correspondent says. Then we remembered the method adopted in the European countries of our birth to remedy the evil, applied it, and since then it is a real satisfaction to see the number of walnuts that grow to maturity. The remedy is this: We continually break with the fingers all the young shoots which can be easily reached, and to the balance of the tree or trees we give a good sound thrashing with a long, slender pole. This thrashing is directed against, and has for its objeot to break, all the young shoots of the tree, and thus to compel the vital force to expend itself in forming fruit strong enough to arrive at maturity. A. Van der Naillen. U Post St., S. F."
Which implies that the thrashing is breaking off small shoots similar as above to stimulate fruit (nut) growth.
Walnut trees we had access to (Juglans regia) were usually a biennial cropper but that may have been climate driven in that particular location..
A lot of heavy cropping trees seem to do that. The acorns around here certainly do it naturally, and apricots are notorious for being biennial croppers (although you can "fix" that with them some by thinning fruit aggressively on the heavy years and they'll produce more then next year when they'd normally be off a bit)