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

Deborah S Page-Dumroese,Joanne M Tirocke,Steven T Overby,Matt D Busse,Brian D Gardner

doi:10.4236/ojss.2015.51002

Abstract

Soil quality assessments are essential for determining impacts on belowground microbial community structure and function. We evaluated the suitability of active carbon (C), a rapid field test, 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. Our results indicate 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.

Highlights

Changes in the labile fraction of the soil organic matter pool can provide an indication of both short- and longterm changes in soil quality that are a direct response to land management practices
Active C was less in the managed stand; whereas substrate-induced respiration method (SIR), respiration at day 8, bacteria and hyphal biomass were greater 40 years after management, but not significantly (Table 3)
In our 40-year-old harvested stand, moderate changes in soil bulk density, cation exchange capacity and some PFLA measurements indicate that the soil environment is still exhibiting chemical, biological and physical changes due to harvesting

Summary

Introduction

Changes in the labile fraction of the soil organic matter pool can provide an indication of both short- and longterm changes in soil quality that are a direct response to land management practices. Volcanic materials have undeveloped crystalline structure and weather rapidly in humid environments, producing soils that are characterized by high water holding capacity, cation exchange capacity, and their ability to stabilize organic matter [9] These soil types are widely distributed in northern Idaho and support highly productive forests [10]. Given that a rapid assessment of soil microbial response to land management is needed and that a measure of biological activity should reflect organic matter quality, our objectives were to 1) test the rapid field measure of active C as an indicator of soil biological quality, and 2) determine the long-term impact of forest harvesting on soil microbial and chemical properties

Objectives

Methods

Results

Conclusion