Walnut trees grow like weeds here; they are well-adapted to our local conditions. The soil is a stony clay about 2 feet thick, over well-drained calciferous rock, the summers can be long, hot and dry, all of which can make life difficult for small trees.
The first thing a walnut seedling (nutling?) does is send down a deep tap root to chase the water up from deep in the ground. Self-seeded walnuts seem to survive the hottest summers, but transplanting them, which cuts the tap root, never works.
The walnut nutling will have a single vertical branch that shoots up quite quickly. However, this represents a tasty morsel for deer, boar and hares that eat the shoot or gnaw the bark off the stem. But if the upper part of the tree is killed, the root just sends up several more branches to replace it. These tend to shield each other so the tree has a chance of finding a leader shoot that remains uneaten, until it hardens.
Apparently, it's not good to put walnut shreddings onto compost heaps as they prevent the decay, so they have some kind of bug protection too.
And they make walnuts. Excellent.