How can I help a person in reviving his trees

Gift cards are a reward for assisting other farmers. When you visit another farm and fill a crate on a boat or revive a tree/bush, the item will be left with your icon. The farmer can then tap on it which sends you a thank you letter. Some of the letters will contain gift cards. You can get a maximum of 5 gift cards per day no matter how many thank you letters you receive. Likewise, if someone helps you, you can tap on their icon to send them a thank you note. You have to tap twice for the Trees and Bushes. The thank you letters are delivered daily to the blue mailbox at the front of your farm. You do not have to be connected to facebook to earn gift cards.