Early impacts of forest restoration treatments on the ectomycorrhizal fungal community and fine root biomass in a mixed conifer forest

1. The obligate symbiosis formed between ectomycorrhizal fungi (EMF) and roots of tree species in the Pinaceae influences nutrient uptake and surrounding soil structure. Understanding how EMF respond to prescribed fire and thinning will assist forest managers in selecting fuel-reducing restoration treatments that maintain critical soil processes and site productivity. 2. The response of EMF species richness, live fine root biomass and duff levels to various forms and combinations of thinning and burning was investigated in mixed ponderosa pine and Douglas fir stands in the Blue Mountains of Oregon. The below-ground community composition and structure of EMF at the site was characterized using molecular methods. 3. The EMF community consisted of a large number of infrequently detected species. The distribution of a few abundant species (Cenococcum sp., Piloderma sp., Rhizopogon salebrosus and Wilcoxina rehmii) in a majority of the treatments both before and after treatment application demonstrates that some EMF species survive or rapidly re-establish after disturbance. 4. EMF species richness, live root biomass and duff levels were reduced significantly by prescribed fire treatments compared to the non-burned treatments. 5. Synthesis and applications. These results indicate that prescribed fire results in a short-term reduction in EMF species richness and live root biomass and may influence whether managers can achieve the desired future condition of stands with large-tree retention and low fuel loads. EMF mortality and complete duff reduction after fire have been implicated with poor tree survival and slow stand recovery in forest ecosystems world-wide. The results of this study, along with the recovery potential of a site, and the impending risk of stand-replacing wildfire in stands differing in structure from historic conditions, bear consideration when reintroducing fire.