Pelletized inoculation of fire mosses in severely burned conifer forests overcomes initial barriers to Bryum argenteum establishment but does not increase cover

As wildfires increase in extent and severity, we need new tools to rehabilitate burned landscapes. We tested the effectiveness of adding fire moss tissue, produced in the greenhouse, as a bio-inoculant to severely burned soils in dry mixed conifer forests. We conducted three sequential experiments using knowledge gained from previous experiments to fine-tune fire moss delivery methods. The first two experiments began in July 2017, less than ten days after a wildfire in Arizona, United States. First, we added disaggregated (passed through a 2 mm sieve) cultivated moss tissue to burned soil surfaces, which was immediately collected by ants. In a second experiment, we added two preparations designed to reduce ant collection: moss rolled into pellets using diatomaceous earth and moss ground to a powder. Pelletization increased Bryum argenteum cover (F_[3,55] = 12.32, p < 0.001) and the number of distinct moss colonies (F_[3,55] = 11.87, p < 0.001) when compared to untreated control plots, although cover remained low (1%). A third experiment took place four months postfire in New Mexico. Sieved moss, pelletized moss, and pelletized moss at a high (5×) application rate were added to a burned forest. The high-rate pelletized treatment increased B. argenteum colony count by 140% compared to controls (F_[3,44] = 2.37, p = 0.084), but did not increase cover (F_[3,44] = 1.19, p = 0.325). At both sites, an extreme drought (Palmer Drought Severity Index < −4) during the winter of 2017–18 likely reduced success. We recommend further refinement and testing of pelletization in non-drought conditions.