Chapter I
CONCLUSIONS

On a site with soils that are not highly susceptible to compaction, increased bulk density caused by stump removal does not seem to be a long-term concern. The small increases seen on these sites are not likely to impact tree growth. The recovery seen at Sweethome indicates that surface soils can recover fairly rapidly from increased bulk density that has been caused by the heavy equipment.

The different soil types on these five treatment sites showed similar results in that most soils had a small, non-significant increase in bulk density, and a large decline in mineral soil nitrogen concentration and forest floor depth.

The results presented here show an increasing reduction of nitrogen levels with increasing disturbance. The reduction in nitrogen levels increases from unharvested forest to clear-cut to clear-cut with stump removal.

It seems clear from this study that when deciding whether a site is suitable for stumping treatment, in addition to considering the physical properties of soils and operational procedures that minimize forest floor and mineral soil disturbance (Quesnel and Curran 2000), the productivity of the site, nitrogen pools and nutrient cycling must be considered. A low productivity site may not be suitable or it will need fertilization or organic matter inputs after stumping treatments. The continuing evaluation of growth and foliar data on these sites will give a better idea of long-term effects of N losses on sites with varying N pools. The long recovery time needed to restore soil organic matter and dependence of functioning soil biota and nutrient cycling on soil organic matter must be taken into account in order to determine whether the loss of productivity caused by the additional damage to the organic component of the soil by stump removal for P. weirii control can be offset by the reductions in tree mortality.