The extent of severely burned landscapes are increasing in the Western US due to climate change and altered forest states. Directly after a wildfire, managers implement techniques to stabilize soils or harvest merchantable timber. Collaborating with land managers from the Colville National Forest in Northeastern Washington we built upon a postfire erosion study they had begun. On the 2015 Stickpin Fire, we examined the effects of no treatment, straw mulching, wood shred mulching, and postfire logging on fire moss cover. Fire mosses are non-vascular bryophytes that can rapidly stabilize soils after wildfires. We also examined the cascading effects of moss colonization on postfire nitrogen availability using plant root simulator probes during a winter, October through April, and a spring, April through June, sampling phase.

Consistent with our hypothesis, wood shred mulch, straw mulch, and litter cover inhibited moss cover (F=13.8, p=0.001) across all treatments by reducing the amount of bare soil cover that moss could colonize. Moss colonization was lowest under the straw mulching treatment, but this was likely linked to the fact that straw mulching occurred on a more south facing hillslope that received more direct sunlight. Additionally, we hypothesized that postfire logging would disturb soils reducing moss cover there. We found that moss cover was reduced on some logging skid trails but increased on others when compared to undisturbed hillslopes(t=-1.58, p=0.14).This unexpected result points to the potential for mosses to be used in restoration of skid trails after postfire logging as they often have high erosion rates.

Finally, we explored the impacts of moss colonization on nitrogen availability in the soil surface. Moss cover did not affect ammonia (NH4+) availability (F=0.14, p=0.71) but was negatively related to nitrate (NO3-) availability (F=14.3, p<0.001), especially during the winter vascular plant dormancy phase vs the spring active phase (F=32.7, p<0.001). We believe this due to uptake of NO3-by mosses throughout the winter. Moss uptake of NO3-could reduce vascular plant growth in the short term if nitrogen is limiting, but over a longer term it could also reduce nitrogen loss via leaching and runoff to surface water during spring snowmelt. This research provides a series of results that point to valuable next steps in fire moss research.