Facilitation is a potentially useful tool in restoration efforts. We investigated the causes of facilitation in planted Picea mariana seedlings in an unvegetated mine tailings dump. Clusters of plants doubled the survival rate in the first growing season compared to single plants. In the first year mycorrhizal inoculation had no effect on survival, but by the second growing season only mycorrhizal inoculated plants survived, most of these being in plant clusters. This suggests that facilitation in this environment is partly the result of interactions with mycorrhizae.