Trees can be divided into two groups: deciduous trees, which lose all their leaves in autumn and evergreens, which keep leaves on their branches throughout the year.
Evergreens, such as holly, usually have leaves which are covered in a thick layer of wax to stop them losing too much water. Conifers, such as pine trees, are evergreens which have long narrow leaves. This shape of leaf also helps to reduce water loss.
The sap of trees which live close to the Arctic is also special. In winter their sap becomes rich in sugars which stops the sap from freezing, in other words, it acts as an antifreeze. In the sugar maple the sap is particularly rich in sugar. In North America the sap of the sugar maple is collected for food.
