Forest Co-op ES 11 & 12 Shallow Soils Monitoring Project - Phase 2
The practice of full-tree logging on shallow soils (less than 20cm) in Northwestern Ontario is currently a ‘not recommended’ (NR) practice in Ontario’s silviculture guides. If undertaken during forest management, it must be accompanied by exceptions monitoring. To fulfill this requirement, the Shallow Soils Monitoring Project was established in 2001. Financial support was provided through an OMNR-forest industry partnership administered by the Forest Co-op.
This project was established to evaluate the sensitivity of shallow soiled sites to nutrient loss by comparing operational tree-length (TL) and full-tree (FT) logging treatments. In total there were 472 (227 FT and 245 TL) plots established on 7 case study sites across the region. Each case study site treatment area was approximately 10 hectares. An additional 99 FT plots (Level 2) were established with a less intensive protocol and on very shallow site conditions. These plots were intended to provide an estimate of the regional-level variability of responses to full-tree logging on these deemed sensitive sites.
In 2008, the project team assessed the 7 case study sites and 90 of the level 2 plots. On the case study sites, these fifth year post-harvest assessments consisted of collecting data to determine levels of available soil nitrogen (index of soil quality), regeneration status (stocking, density, species composition), and crop-tree performance (growth and foliar nutrition). The level 2 plots were assessed for regeneration density, species composition and relative clumpiness of the regeneration.
The stocking of trees on the case study sites ranged from 27 percent to 86 percent for full-tree logged and 35 to 75 percent for tree length-logged treatments. Overall there was no difference in stocking due to logging treatment with a mean of 71 percent and 74 percent for full-tree and tree-length logging treatments respectively. Likewise for stem density, there was no significant difference over all case study sites in the number of stems per hectare with values of 6500 stems/ha for full-tree logged and 5430 stems/ha for tree-length logged sites. The average mineralizable nitrogen in the soil layers for both treatments was 28 kg/ha with no significant harvest treatment effect.
Overall there were no trends in the fifth year assessment data from the case study sites that would lead one to speculate that one logging treatment performs better than the other. The nature of these rugged sites and undulating topography likely have a greater influence on the variability found in the data than the treatment at this point in time. These sites are still in the recruitment phase of stand development, therefore, it is likely that the nutrient demand of the relatively small seedlings is less than the site-level supply. These preliminary data, however, do provide base-line levels that will be combined with the results from the 10th year assessment to evaluate the change in available soil nitrogen, regeneration and crop tree performance over time. It is the comparison of these rates of change that could indicate whether nutrients may be limiting on a specific site and treatment combination.