Interactions among Prescribed Fire, Soil Attributes, and Mycorrhizal Community Structure at Crater Lake National Park, Oregon, USA

Abstract

We identified relationships between prescribed burn treatments and selected soil and fuel attributes on mycorrhizal fungus fruiting patterns in an old-growth ponderosa pine (Pinus ponderosa) and white fir (Abies concolor) stand in Crater Lake National Park, Oregon, USA. Three prescribed burn treatments (early spring, late spring, and fall burns) plus non-burned controls were applied to 24 ∼3 ha units in 2002. We sampled mycorrhizal fungus sporocarp production in the spring and fall in the ensuing three years, and collected data on surface fuels, soil C and N concentrations, δ13C and δ15N signatures, pH, and mineral soil bulk density. A gradient of C:N ratios and other soil attributes across the study area facilitated separation of the effect of fire from the effects of soil attributes on fungal fruiting patterns. Distinct guilds of fungal indicator species were identified, correlating more closely with soil C:N ratios than prescribed burn treatments. Although other habitat attributes (such as fuel levels) were correlated with C:N ratios, the C:N ratios were the most consistent predictor of fungal fruiting patterns. The fall burn treatment did reduce soil C:N ratios, and most of the fall burned units produced the fungal indicator species associated with lower C:N ratios, but the same fungal indicator species also fruited in the non-burned control units with lower C:N ratios. The spring burn treatments did not differ significantly from non-burned controls in fungal fruiting patterns or C:N ratios. Fall burn treatment units produced significantly fewer fungal species and collections than spring burn units, but did not differ significantly in fungal diversity and abundance from non-burned controls.