1.Trees are valuable to mankind for a number of reasons. 2.Many trees are major sources of food, primarily as fruits and nuts ; also, sugar is derived from the sap of some trees. 3. Wood is a major source of fuel for heating and cooking, particularly in developing counties. 4.Construction materials from wood include lumber, plywood, and particle board. 5.Wood is the major source of fiber for the production of pulp and paper. 6.Trees are a primary or secondary source for many chemical products. 7.Some fibers, such as rayan, are produced from wood pulp. 8.The bark of some tree species is the major source of tannins. 9.Other chemicals are harvested directly from living trees such rubber and various reins, which are then refined to products as turpentine.