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Ectomycorrhizal communities of Douglas-fir and paper birch along a gradient of stand age following clearcutting and wildfire in the Interior Cedar-Hemlock zone, southern British Columbia Twieg, Brendan David


Ectomycorrhizal (ECM) communities of Douglas-fir and paper birch were characterized in 5-, 26-, 65, and 100-year-old stands using ECM root tip morphology and ITS region DNA sequences. Stands disturbed by wildfire (all age classes) and clearcutting (two youngest age classes) were studied (4 replicates per stand type) in the Interior Cedar-Hemlock forests of southern British Columbia. ECM community species richness on Douglas-fir differed with stand age, being three times higher in 65- and 100-yr-old stands than 5-yr-old stands; 26-yr-old stands were intermediate. In the 5-yr-old stands, the ECM community of paper birch had ~70% higher species richness than Douglas-fir. Roots of sprouting paper birch stumps may support mycorrhizae or inocula that persist through disturbance. Overall ECM diversity increased substantially from 5- to 26-yr-old stands, but changed little with further stand age increase. ECM community composition and structure shifted from 5- to 26-yr-old stands and continued to change from 26- to 65-yr-old stands, including increases in Russula and Piloderma relative abundances. Similar ECM communities occurred on 65- and 100-yr-old stands. Cortinurius and Hebeloma were nearly absent in 5-yr-old stands and peaked in relative abundance in 26-yr-old stands. Generally, patterns in relative abundance of fungal taxa with stand age paralleled those in frequency. Host-specific ECM fungi were most dominant in the youngest stands, particularly Rhizopogon vinicolor-type on Douglas-fir and Lacturius pubescens on paper birch. Host-generalists were more abundant on paper birch than Douglas-fir at younger ages, suggesting that paper birch may be important in the establishment of these fungi on Douglas-fir. Paper birch also had an important positive influence on ECM fungal diversity in 5-yr-old stands, which should be considered in forest management. There was no difference in ECM diversity between clearcut and wildfire origin sites, although community structure differed slightly between these disturbances in 5-yr-old stands. Within the range of ages studied, it appears that the ECM fungal community changed little after 65 years following disturbance. Available P was correlated with abundance of two dominant taxa, but available N and P, mineralizable N, and organic P were not related to ECM diversity or community structure.

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