Recall the surrounded cities from the days of Joshua!
When we are happy on Purim for the miracles we had in the past, and "recall surrounded from the days of Joshua", we remember the great spirit of Joshua and Caleb, who stood in front of all the difficulties and defeated the fortified towns protected by a wall.
Tu B'Shevat signals renewed vitalization in nature. Some Halachic ramifications of the New Year for the trees, the parallel to the spiritual renewal of man on our New Year, and how our daily, monthly and yearly "timetable" is intimately connected with the Land of Israel.
Joseph the righteous has for generations served as a symbol and model for the survival of the Jewish people in foreign lands. Just as Joseph retained his moral distinction despite being cut off from his home, so did Jacob’s children and their progeny.