Local species communities result from assembly processes that can be conceptually envisaged as environmental filters, biotic filters and stochastic processes. While a large body of ecological literature has reported the importance of environmental filtering in structuring different kinds of communities, there is very limited direct empirical evidence on the relative roles of biotic filtering and stochastic processes in determining community assembly. In this research proposal, I aim to fill this knowledge gap using wood-inhabiting fungi as case study. My study design, which is based on inoculating fungal strains to both naturally fallen and artificially felled logs, provides an exceptional opportunity for assessing the effects of biotic interactions (in particular priority effects) and stochasticity under natural conditions. The study design will enable evaluating how the colonization success of the inoculated species depends on the resident community, and conversely how the colonization success of the inoculated species influences the future development of the resident community. My proposal builds on the distinct advantage of fungi, namely the possibility of manipulating in the field their species-rich metacommunity systems, and replicating the experiment over hundreds of local communities. The results from this study have a high potential to provide ground-breaking impacts on the ongoing development of predictive and conceptual frameworks of community ecology. At the same time, this study has the potential of developing fungal inoculations as a pragmatic conservation tool, which combined with more conventional conservation methods will reply to the urgent need of counteracting the ongoing biodiversity crisis.