The mishnah in Masechet Rosh Hashana 2a tells us that Tu Beshvat is the Rosh Hashana for the trees. There are those that extrapolate from our Rosh Hashana, which is a time of judgment for us, that Tu Beshvat is a time of judgment for the trees. Meaning, that the year's produce from trees being plentiful or scarce is fated on Tu Beshvat. However, this assertion is contrary to the Gemara in Rosh Hashanah 16a, which claims that there are four specific times in the year when judgment takes place: Tishre is the time of judgment for mankind, Pesah is the time for the wheat, Sukot the time when the yearly rainfall is determined, and on Shabouot the supply perot or fruit is determined. Therefore, Tu Beshvat is not the time when this occurs. We may then ask, what function does Tu Beshvat serve? In hilchot Orlah, which stipulate how one may not enjoy the fruit of a tree that was planted within the first three years, Tu Beshvat is used to accurately calculate the age of a tree.