The Effects of in-Bush Chipper Debris on Soil Microclimate Conditions, Leachate Chemistry, and Tree Seedling Survival and Growth.

In-bush chipping is a common practice across northwestern Ontario, which generates considerable roadside waste and has resulted in poor tree seedling regeneration.  Factors that have been suggested for this poor survival include: a physical barrier impeding root development, changes to soil temperature and moisture regimes, and/or toxicity to leachate generated from these waste wood piles.  In this study, both fresh (1-year-old) and old (8-year-old) chipper debris piles were instrumented to monitor soil temperature and moisture, and to collect leachate via no-tension lysimeters.  The piles were also planted with jack pine and white spruce, and assessed after the first two growing seasons (survival, health, growth).  A 16-week greenhouse trial was also conducted to examine the direct effects of watering potted seedlings with leachate versus rain water.  There was a noticeable lag in soil temperature warm up in the spring under the debris piles when compared to soil temperatures in the adjacent cutover, but diurnal fluctuations were considerably less.  Soil moisture content remained higher under the debris piles than the adjacent cutover area throughout the growing season.  Initial seedling survival was high for both ages of debris piles, but a much higher number of seedlings were chlorotic or had browning needles, particularly on the fresh debris piles, suggesting mortality may increase over time.  Watering with leachate had a significant effect on jack pine relative growth rate, but white spruce seedlings were not affected.  Forest management practices that increase debris carry back during logging operations, and double pass site preparation with power trenchers are recommended to reduce the effects of debris piles on soil microclimate conditions, improve drainage, and increase tree seedling regeneration success.