Decomposition of dead organic matter is essential for ecosystem functioning and nutrient cycling, but carrion, leaf litter, and deadwood vary in their physicochemical characteristics, associated decomposer communities, and consequently in the rates at which they are decomposed. Despite being well studied separately, how carrion, leaf litter, and deadwood decompose under similar conditions is less well known. We conducted an experiment to quantify the effects of arthropods, canopy openness, and forest-management intensity (ForMI) on decomposition rates of carrion, leaf litter, and deadwood in temperate forests. We found that carrion decomposition was up to 90 times faster than decomposition rates of leaf litter and deadwood, which decomposed at similar rates. The presence of arthropods accelerated the decomposition of carrion by 2.8 times relative to when they were absent, highlighting how arthropods are an important driver of carrion decomposition. Canopy openness increased leaf litter decomposition when arthropods were present, and it mediated effects of arthropods: For leaf litter, arthropods accelerated decomposition in gaps but had a marginally decelerating effect in closed forest. For deadwood in canopy gaps, arthropods marginally decelerated decomposition. ForMI had no effects on any decomposition. Our findings demonstrate that arthropods and canopy openness interactively shape decomposition processes, but their relative effects differ between carrion, leaf litter, and deadwood. This highlights that patterns of decomposition rates in response to environmental drivers cannot be generalized across different types of dead organic matter. Increasing natural disturbances and harvesting leading to increased canopy openness will most likely affect the decomposition processes of leaf litter positively and deadwood negatively.