A Closer Look at Fungal Community Changes After Mountain Pine Beetle Outbreaks

Mountain pine beetles have dramatically changed forest landscapes in Western North America by killing-off large areas of trees and changing soil communities. Soil community structure is complex, and tree death can create implications for other organisms. By examining a recent beetle outbreak in lodgepole pine forests of western Canada, the authors look at the effects of tree death on fungal communities in the soil. In particular, the study analyzes two types of fungi, ectomycorrhizal and saprotrophic, to determine the changes in richness and composition of the fungal community during tree mortality.

The mountain pine beetle is native to temperate conifer forests in western North America, but it has expanded into areas east of the Rocky Mountains and as far north as the Boreal Forest. Previous studies have shown a decrease in ectomycorrhizal fungi in beetle outbreak areas. This study builds on the previous research to look closely at the changes in fungi richness and composition after a beetle outbreak. Variations in environmental factors and geographical distance are determined to understand how they influence fungal community richness and composition.

Pec et al. (2017) studied eleven lodgepole pine stands in the Lower Foothills natural subregion southwest of Grande Prairie, Alberta. The area had been experiencing impacts from mountain pine beetles since 2009. The study collected soil samples from eleven plots. It was found that tree death from the mountain pine beetles changed the fungal community richness and composition due to a decline in ectomycorrhizal and saprotrophic fungi populations. Environmental factors, like soil nutrients, and geographical location also influenced the overall fungal community.

Dependent on a host tree for carbon, ectomycorrhizal fungi experience a severe reduction in carbon availability after tree mortality. The fungi are sensitive to soil conditions and as nutrients decreased, so did the population. Saprotrophic fungi populations were less affected by soil nutrient levels. However, their populations were found to be “weakly but significantly correlated with the geographical distance of the plots.”

Tree mortality, soil chemistry, and geographical factors independently changed the composition of the fungal community. Pec et al. (2017) believe large areas of tree mortality from bark beetles may trigger a chain of events that act on the soil conditions and act separately on fungi. Many fungal species are either directly or indirectly dependent on pine trees for resources, and widespread death will have implications for soil communities.

This is an article written by Michelle Murphy. For more information, please access the full document:

Pec, G.J., Karst, J., Taylor, D.L., Cigan, P.W., Erbilgin, N., Cooke, J.E.K., Simard, S.W., Cahill Jr, J.F. (2017). Change in soil fungal community structure driven by a decline in ectomycorrhizal fungi following a mountain pine beetle (Dendroctonus ponderosae) outbreak. New Phytologist.

 

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