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Impacts of Forest Harvest on Active Carbon and Microbial Properties of a Volcanic Ash Cap Soil in Northern Idaho

Changes in the labile fraction of the soil organic matter pool can provide an indication of both short- and long-term changes in soil quality that are a direct response to land management practices. Assessments of soil quality often include a measure of soil organic matter, because it is critical for maintaining site productivity.

In forest soils, organic matter content has been linked to soil water availability, nutrient supply, soil aggregation, and disease incidence or prevention and contributes to numerous soil functions. Forest harvest or site preparation activities that remove the surface organic horizons may cause changes in soil organic matter that affect long-term productivity.

In this study, the authors evaluated the suitability of active carbon (C) as an indicator of soil biological quality in five paired forest stands (clear cut harvested 40 years prior and unharvested) growing on volcanic ash-cap soils in northern Idaho. Active C was compared with several traditional measures of soil microbial properties (microbial biomass, respiration, fungal hyphal biomass, bacterial number and biomass and PLFA community structure).

Despite the significant differences in forest vegetation between paired stands, no differences in active C and only a few significant differences in microbial properties were detected. Total bacteria (microscope counts) and PLFA signatures (gram positive bacteria, gram negative bacteria, actinomycetes) were significantly higher in the managed stands. The results indicated that either mineral soil biological properties in managed stands were relatively unaffected at the time of harvest or some biological recovery occurred 40 years later. Additionally, volcanic ash-cap soils in moist ecosystems could be highly resilient to the impacts of harvest operations and therefore few significant biological changes could be detected.

In conclusion, active C can be used to estimate the most readily oxidizable (active) forms of soil C and this measure is related to other microbial measures such as SIR, basal respiration, PFLA fungi and the total C pool. Also, this method determining the labile soil C pool provides a low-cost tool for forest land managers who are interested in determining changes in soil quality from harvest or site preparation practices.

Article by Deborah S. Page-Dumroese, et al, from USA.

Full access: http://t.cn/E4qPYeI
Image by SylvainB_, from Flickr-cc.

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