Except for Beech and Sassafras, I have successful plantings of these trees as a backup food source for goats but they can supply human food though mostly in the spring.
Northern Trees with Edible Leaves
Beech- young leaves have a flavor somewhere between lemon and sorrel and are a tasty salad green.
Basswood (Linden)- The leaves of linden are a delicious when salad green when eaten young with the crunch that iceberg lettuce and more nutrition. The leaves can also dry and grind them into a powder for addition to soups.
Birch- Birch leaves offer a hint of bitterness that in small amounts, mixed with other greens in salads similar to radicchio. The dried leaves can be used for herbal tea combined with mint.
Hawthorn- Before the flowers or berries appear, the leaves are at their best, with a rich, nutty flavor. You can eat them in a salad or chop them and sprinkle over dishes as a parsley substitute.
Mulberry- When young, the unrolled leaves are also edible as is, however, the older leaves have a bit of toxicity that can cause a stomachache and need to be boiled before eaten or dried, add to salads or stuffed as if a grape leaf.
Sassafras- The green buds and young leaves are delicious in salads. The dried leaves, veins removed, are used to thickened and flavored soups and stews.
Sugar Maple- Young maple leaves are also edible in into a salad or boil with other spring greens in pottage but bitter as they mature.