One of the fun parts of being a person is that you get to celebrate your birthday—the particular day you came into the world. This is not true for trees. Trees have a generic “birthday”—Tu Bishvat. A sapling becomes a year old at its first Tu Bishvat, two years old the following Tu Bishvat, etc. Why does it even matter how old a tree is? As R. Aviva Richman explains, in the Torah, it matters a lot.