“Tu Bishvat could easily have faded away after the destruction of the Second Temple in 70 CE, since there was no longer a system of fruit offerings or Temple priests to receive them. However, the kabbalists (mystics) of Tzfat (the city of Safed) in the Land of Israel in the 16th century created a new ritual to celebrate Tu Bishvat called the Feast of Fruits.”
So, technically, the birthday, or new year, which begins in the evening of Sunday, Feb 9, and ends in the nightfall of Monday, Feb 10, is only about fruit trees. But the rabbis have extended it to all trees wherever they may be. Including the big grandfather tree off the porch at the mini-rancho.