Ecology of Hypogeous Fungi Associated with Ponderosa Pine

Seasonal abundance and distribution of hypogeous fungi associated with selected stands of ponderosa pine on the Coconino and Kaibab Plateaus, Arizona, were examined using a new method that reduced the time and area needed to sample nonrandomly dispersed fungal sporocarps. As measured monthly over three years, peak sporocarp production occurred both spring and fall with the greatest species richness and abundance in fall. Production was generally initiated when mean air temperature was greater than 8 C and single precipitation amounts exceeded 1.5 cm. Species richness paralleled sporocarp productivity. Sporocarp biomass production was positively influenced by canopy cover afforded by clusters of intermediate aged pines. Sixteen genera of basidiomycetes comprised 90% or more of the annual sporocarp biomass. Rhizopogon evadens, R. subcaerulescens, Gautieria crispa, Hysterangium coriaceum, and Sclerogaster xerophila accounted for 87% of annual sporocarp productivity and were found in every season. Four genera of ascomycetes and one zygomycete genus accounted for 8% of annual biomass. Geopora cooperi and Tuber levissimum were the most prevalent ascomycetes individually contributing 5% or more to total sporocarp biomass in some years. The geographically separated pine stands on the two plateaus have a similar hypogeous mycota. Lower sporocarp production on the Kaibab Plateau was partly attributed to lower precipitation and a preponderance of older age-class trees in a late successional forest. When compared to Douglas-fir stands, annual sporocarp biomass in ponderosa pine was lower and the dominant fungi were markedly different.