decomposer decomposes :) so it breaks down the organic matter into simpler compounds. it's very important process because complex compounds that build living organisms are not absorbable for other organisms, thus chemical cycling wouldn't be possible and the whole ecosystem would shut down. dead plants and animals would be everywhere and new organisms couldn't be born/grown. mold breaks down dead organic matter like dead trees. as the result simple compounds come into existence and can be assimilated by plants
