Take large sheets of plain white paper - not too thick and coloured crayons to your local park/woodlands area.
Place the sheets of paper against the tree trunk and being careful not to rub the crayons against the actual tree, rub them over the paper so that the bark markings show through in stencil fashion.
If you are lucky enough to find some old pieces of bark on the floor - use them in your homes or settings to take additional prints from ~
1. Paint the back and then take a print of the markings by laying a piece of paper over the top and moulding it to the bark - and picking up the paint at the same time .. peel off slowly so that the patterning is fresh and unsmeared.
2. Roll out a large slab of clay or dough - press the bark into the clay so that it makes an impression into it - repeat to build a pattern ~ once dry you can paint the clay or use it to take prints from again !!
Another great use for tree bark is in a soil or sand tray. It can make great 'houses' and living areas for plastic minibeasts
Look at the different types of tree barks that are around... can you identify the name of the tree?