In boreal forests, different types of fungi compete with each other to break down dead plant material. This study found that the fungi living in partnership with tree roots actually slow down the decomposition of fresh pine needles, especially after droughts. However, in older, partially decomposed soil material, the fungi associated with tree roots actually speed up decomposition, while fungi associated with shrubs slow it down. These findings suggest that how quickly different types of fungi decompose forest material depends on what type of dead material they are breaking down.