Example of a decomposer and explain what would happen if decomposers were absent from a forest ecosystem

If the a decomposer were absent from the forest, everything would just pile up onto one another and never be returned to the Earth. 

An example of a decomposer would be a worm. And if there was no decomposers in a forest ecosystem or any where .The simple answer would be : there would be a bunch of dead animal bodies everywhere and then the world would be covered in dead bodies. Plain and simple!