Kayla Scheffler's Honours Thesis Abstract

Intensive forest management practices may differ from natural fire disturbances in its effects on soil properties, such as carbon (C) and nitrogen (N) storage, that may cause long-term changes in stand productivity.  This study compared soil properties of three black spruce (Picea mariana) stands in Northwestern Ontario, which included two disturbed stands and one recently undisturbed control stand.  Both disturbed stands are regenerating areas that had experienced disturbance 20 years prior to sampling; one represents conditions from a natural burn and the other represents conditions of a whole-tree havesting (WTH) with blading treatment.  Soil samples were collected in three established plots within each stand.  The organic layer of the forest floor and the mineral soil (0 - 50 cm) were sampled at three locations in each plot and bulk density samples in the mineral soil were determined.  Both the organic material and mineral soil were air analysed for organic C and N content.  The mineral soil was also analysed for its pH.  Significant differences were observed between the disturbed sties and the control site in these study areas, with disturbance effects being most significant within the WTH with blading treatment.  The burn site had forest floors with thicker organic layers, higher organic carbon masses, lower pH, higher concentrations of total C and N in the mineral soil, and higher C and N storage in the mineral soil compared to the WTH with blading site.  Although significant losses in total N stores within the burn site were observed, C stores did not appear to be affected by the burn.  This may be due, however, to the nature of the wildfire which was described as being a relatively low intensity burn with only a moderate depth of burn into the humus layer.  The WTH with blading site, as mentioned was the most significantly affected by disturbance and the forest floor at this site had significantly lower masses of organic material and significant losses of both C and N stores, with concentrations measuring approximately 45% and 60% less, respectively, than those of the control site.  The decreased organic material and subsequent diminished C content is a direct result of the great quantities of forest volumes taken away during harvesting activities and indicates that this type of harvesting is not a sustainable practice.  Also, this study suggested that WTH with blading can result in significant negative impacts to C  and N stores that are different from those produced by a naturally occurring wildfire.  A final notable finding of this study was that both C and N storage was significantly greater in the organic layer than the mineral soil for all treatments (by approximately 70%), indicating that a larger portion of the C and N content resides in the unprotected labile portion of the system which makes forest floors naturally vulnerable to disturance.  Further study is necessary to determine the stabilization mechanisms of the soil organic matter (SOM) to systematically characterize the physical protection mechanisms of the soil environment.