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Effects of silvicultural practices on ectomycorrhizal fungal communities

We have taken part in a number of interdisciplinary studies that examined how ECM fungal communities in regenerating stands are influenced by silvicultural practices. We use detailed morphological examination, supported by molecular analysis to distinguish mycorrhizas formed by different fungi.

Distance from intact forest

In the subalpine forests of the Engelmann Spruce - Subalpine Fir biogeoclimatic zone of British Columbia, the number of mycorrhizal morphotypes decrease dramatically by 18 months after winter logging (Hagerman et al. 1999a). When young non-mycorrhizal spruce seedlings were used as bait, mycorrhizal colonization and the diversity of morphotypes was 50 % higher in the periphery of clearcuts (2-3 m from the forest edge) than it was at 16 m or greater from the forest edge (Hagerman et al. 1999b). Except at the periphery, colonization and ECM fungal diversity were not different between seedlings planted in the clearcut and in the forest. Interestingly, when commercially produced spruce seedlings were planted on mounds at the same site, no difference in colonization or morphotype diversity were apparent with increasing distance from the forest edge (Jones et al. 2002a). These studies were part of the Sicamous Creek Silviculture Systems Trial established by the BC Ministry of Forests, Kamloops Region. Much of it comprised the M.Sc. thesis of Shannon Hagerman.  We found a similar pattern, although less distinct in the Interior Cedar Hemlock zone in central BC (Durall et al. 1999).

Sicamous Treatments

Unresolved questions

  • Why does the ectomycorrhizal fungal community change following clearcutting? Is this due to changes in inoculum type and amount or to changes in the biological and physical environment? Are the fungi in clearcuts better adapted to these conditions than 'forest fungi'?
  • Which are the most important sources of inoculum in clearcuts?
  • How long does it take for the dominant ECM fungi in regenerating stands to be the same as those found in forests?
  • Do nursery fungi inhibit colonization by indigenous fungi to the extent where we should be discouraged, rather than encouraging, colonization in nurseries?

Clearcut size

Both at Sicamous Creek and at Date Creek, a silviculture systems trial in the Interior Cedar Hemlock Zone in northern British Columbia, distance from the forest was more important than clearcut size in determining the composition of the belowground ECM fungal community. There was a distinct threshold size, however, for impacts on the diversity and productivity of above ground sporocarps of ectomycorrhizal fungi (Durall et al. 1999). Furthermore, we found that truffle production was eliminated by clearcutting and had not returned five years later (Durall, unpublished).

Unresolved questions

  • How long does it take for above ground and below ground production of ECM fungi to return to pre-harvest levels? 
  • What are the most important factors influencing sporocarp production?

Methods of controlling competition from herbaceous plants

On a dry slope in the Interior Douglas-fir zone, competition from grasses had prevented establishment of lodgepole pine. An experiment was established to test the effectiveness of mechanical (spot screefing) vs. chemical (glyphosate) control of competition. At the end of the second growing season, ectomycorrhizal diversity was reduced on plants in the mechanical treatment compared to those in the chemical treatment (Jones et al. 1996; Simard et al., submitted). This effect was rather small and transient; one year later it had disappeared.

Planting mixtures of tree species

In 1991, Suzanne Simard of the BC Ministry of Forests, Kamloops Region (now Forest Sciences, University of British Columbia Vancouver) established a relative addition study comprising paper birch growing in different proportions and densities with Douglas-fir, western larch, and western redcedar. We examined the ectomycorrhizal morphotypes on root systems of birch and Douglas-fir at the end of one to three growing seasons. The evenness (but not richness or diversity) of morphotypes was somewhat higher (P = 0.08) on Douglas-fir planted with birch than on Douglas-fir grown in single-species plots (Jones et al. 1997). This treatment effect was no longer detectable after 7 growing seasons (Jones, unpublished). Ninety % of the ectomycorrhizal root tips of birch were colonized by fungi also associated with Douglas-fir. Fifty-six % of the ectomycorrhizal root tips of Douglas-fir were colonized by fungi also associated with birch.

Unresolved questions

  • Are birch and Douglas-fir colonized by the same fungal individual? If so, what is the significance of this? Can one intact mycelium connect root systems of the two species?

This question is being addressed by Kevin Beiler in M.Sc. thesis.

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Last reviewed shim4/8/2015 12:30:41 PM