An artificial tree trunk can be a very simple project using materials from your recycling pile. Decide on what kind of tree you would like to replicate and keep in mind the shape and texture of the tree trunk.
Create a tube out of cardboard using a big, tall piece of cardboard. Take an old, open box and cut along one corner. Spread the sheet of cardboard flat on the floor. Cut long slits into, but not through, the cardboard lengthwise from the top to the bottom of the piece using a box cutter. Start from one edge of the piece and move out every 2 to 5 cm (1 to 2 inches) until the entire piece is covered with slits. This will make the cardboard pliable. Roll the cardboard into a tube shape, overlapping the top in order to create a wider base. Once the shape is complete, tape the tube in place using a strong tape like duct tape.
Use paper mache to cover the cardboard base. Cut 25- to 50-mm (1- to 2-inch) strips of newspaper. Mix one part flour with one part water to create a paste. Dip the strips of newspaper in the paste mixture and begin to cover the cardboard tube. Add one layer of paper mache to the tube, overlapping enough to make sure it has no exposed areas. Once this layer has dried, add a second layer of paper mache. In this layer, crumple the paper strips a bit in order to create a trunk-like texture.
Paint the artificial tree trunk the desired colour once the paper mache is completely dry. Try using a dark base coat and highlighting by applying a lighter colour with a roller. This will emphasise the texture of the trunk and create a more authentic look.
To add branches to the trunk, make multiple tubes of cardboard and tape them together before adding the paper mache. Paper mache drying times vary depending on the climate you are working in. Add salt to the mixture if you live in a humid area.
Make sure the base is wide enough to create a steady tree, or that you secure it to the ground. If the layers of paper mache are too thick or do not dry thoroughly, they can become mouldy.