Mycorrhization of Ponderosa Pine in a Second-growth Sierra Nevada Forest

—Ectomycorrhizal colonization and rooting characteristics were quantified in a mature ponderosa pine (Pinus ponderosa Dougl. ex Laws.) stand in the western Sierra Nevada. Root length totaled 3835.9 m ⋅ m–2 of forest floor surface area, with 96% consisting of the fine-root fraction. Total root dry weight and volume were 2230.4 g ⋅ m–2 and 5807.4 cm3 ⋅ m–2 of forest floor area, respectively, with 69% of the former and 75% of the latter accounted for by the coarse fraction. Fine roots were most prevalent in the upper 15 cm of the mineral soil profile, and their abundance declined with increasing depth. Coarse roots were most abundant at a depth of 15–30 cm. Ectomycorrhizal counts totaled 26,814 ⋅ m–2 of forest floor area, and an overwhelming preponderance was associated with the fine-root fraction. More than three-quarters of mychorrhizae resided in the upper 15 cm of mineral soil, with an overall trend of declining numbers with increasing depth. Roots and mycorrhizae were exceedingly scarce at a depth of 45–60 cm, and neither was found in the organic soil layer above the mineral profile. A necessary step in understanding the ecophysiological role of mycorrhizae in mature forests is to quantify their abundance in such settings, and the results of this study contribute such information for ponderosa pine.