Response of microbial processes and fungal community structure to vegetation management in mixedwood forest soils

Abstract

Previous research to determine the impacts of harvesting and site preparation on microbial processes and decomposer fungi in mixedwood forests indicated that effects were minimal. As an extension to this research, the present study was conducted to evaluate if microbial processes and decomposer fungi were sensitive to manual or chemical vegetation management in addition to harvesting and site preparation. The impact of vegetation management on microbial processes and decomposer fungi was examined in organic and mineral soil from harvested sites in northwestern Ontario. Three vegetation management treatments were applied to three clear-cut and prepared sites 2 years prior to the initiation of the study. Four treatments were established within each site: (i) harvested (control), (ii) glyphosate herbicide (Vision®), (iii) triclopyr herbicide (Release®), and (iv) manually operated brushsaws. The objective of the study was to determine the response of basal respiration, microbial biomass C, metabolic quotients (qCO2), microbial carbon : soil organic carbon ratio (Cmic/Corg), nitrogen mineralization, and fungal community structure to vegetation management by chemical and manual means. Relative to the harvested control, vegetation management had no significant impact on fungal community structure as evidenced through rank abundance curves and indices of fungal community richness, diversity, evenness, or dominance. Although the abundances of the majority of fungal species were not impacted by vegetation management, herbicide and brushsaw use decreased the isolation frequencies of Mortierella vinacea (Dixon-Stewart) and Paecilomyces carneus (Duché and Heim) Brown and Smith, respectively. Occurrence of Paecilomyces carneus was significantly greater in the organic soil than in the mineral soil of the harvested control, but this difference was not detectable in the blocks that had undergone vegetation management. Two years after vegetation management was imposed there were no detectable effects on basal respiration, microbial biomass C, qCO2, Cmic/Corg, or nitrogen mineralization in either the organic or mineral soil layers as compared with measurements made in the harvested control plots.Key words: harvesting, herbicide, brushsaw, fungal community, microbial processes.