Clear‐cutting on wetlands of the St. Lawrence lowlands raised the water table levels on seven of the eight studied sites encompassing five forest types and four soil subgroups. Water table levels dropped 3 cm after clear‐cutting on the eighth site, which was the wettest site with precut water levels within the top 10 cm. This was explained by evaporation from exposed water surfaces. The magnitude of the water table rises increased with the depth of the precut water table. The seasonal mean and maximum rise were respectively 20 and 52 cm on a poorly drained mineral soil which had the lowest precut water table levels. The smallest rises, with means around 7 cm, were associated with high precut water table on bogs and on fens. The watering up was not reduced on fens where a lateral flow occurs. This study indicated that transition sites between the bogs or fens and the uplands were most susceptible to hydrologic changes after clear‐cutting. Watering up was caused by reduced evapotranspiration, of which the major component was interception. The rise of the water table observed in the clear‐cut and the bordering forest indicates that clear‐cutting in narrow strips is not an effective solution to avoid water table rise. Silvicultural treatments to maintain interception and transpiration by leaving logging debris, small trees, and preestablished regeneration would be more effective.

The growing demand for renewable, carbon-neutral materials and energy is leading to intensified forest land-use. The long-term ecological challenges associated with maintaining soil fertility in managed forests are not yet known, in part due to the complexity of soil microbial communities and the heterogeneity of forest soils. This study determined the long-term effects of timber harvesting, accompanied by varied organic matter (OM) removal, on bacterial and fungal soil populations in 11- to 17-year-old reforested coniferous plantations at 18 sites across North America. Analysis of highly replicated 16 S rRNA gene and ITS region pyrotag libraries and shotgun metagenomes demonstrated consistent changes in microbial communities in harvested plots that included the expansion of desiccation- and heat-tolerant organisms and decline in diversity of ectomycorrhizal fungi. However, the majority of taxa, including the most abundant and cosmopolitan groups, were unaffected by harvesting. Shifts in microbial populations that corresponded to increased temperature and soil dryness were moderated by OM retention, which also selected for sub-populations of fungal decomposers. Biogeographical differences in the distribution of taxa as well as local edaphic and environmental conditions produced substantial variation in the effects of harvesting. This extensive molecular-based investigation of forest soil advances our understanding of forest disturbance and lays the foundation for monitoring long-term impacts of timber harvesting.

Reductions in soil porosity through compaction and losses in nutrients through site organic matter removal are considered potentially detrimental effects of forest operations to site productivity. Defining sustainable forest practices is complicated, however, by the possible contrasting responses of commercial tree species to these disturbances. We compared the productivity and foliar nitrogen (N) nutrition of lodgepole pine (Pinus contorta Dougl. ex Loud.) and hybrid white spruce (Picea glauca × engelmannii [Moench] Voss) at Year 12 across organic matter removal and soil compaction treatments in the subboreal forests of central British Columbia. Nitrogen availability peaked in the years following tree harvest, and by Year 12 in situ rates of net N mineralization were uniformly low across treatments. Low rates of N supply were partially offset by intermediate disturbances (forest floor removal alone or compaction through forest floors), which increased N uptake and height growth for hybrid white spruce. Lodgepole pine, in contrast, had near adequate foliar N concentrations and higher tree productivity across the complete gradient of soil disturbances. Some advantage in N nutrition for lodgepole pine might be provided by ectomycorrhiza through host‐specific Suillus species. Fruiting bodies of Suillus species had, on average, 40% higher N concentrations than other common ectomycorrhiza (ECM) fungi found across the plots. The large and often contrasting differences in growth and N nutrition between lodgepole pine and hybrid white spruce demonstrate the possible challenges in defining universal criteria for detrimental soil disturbance.

Roadside processing of wood biomass leaves chip piles of varying size depending upon whether they were created for temporary storage, spillage, or equipment maintenance. Wood chips left in these piles can generate leachate that contaminates streams when processing sites are connected to waterways. Leachate toxicity and chemistry were assessed for pure aspen (Populus tremuloides Michx.), lodgepole pine (Pinus contorta Dougl.), hybrid white spruce (Picea engelmanniiˆglauca Parry), and black spruce (Picea mariana (Mill.) Britton) as well as from two wood chipping sites using mixes of lodgepole pine and hybrid or black spruce. Leachate was generated using rainfall simulation, a static 28-day laboratory assay, and a field-based exposure. Leachate generated by these exposures was analyzed for organic matter content, phenols, ammonia, pH, and toxicity. Findings indicate that all wood chip types produced a toxic leachate despite differences in their chemistry. The consistent toxicity response highlights the need for runoff management that will disconnect processing sites from aquatic environments.

The mountain pine beetle epidemic is changing British Columbia forests and watersheds at the landscape scale. Watersheds with dead-pine-leading stands in the Vanderhoof Forest District of central British Columbia are reported to have wet soils due to raised water tables. They report a conversion of summer logging ground (dry firm soil) to winter logging ground (wetter less firm soil), upon which forestry equipment operation is difficult or impossible before freeze-up. This paper outlines a project that explores this serious operational issue through the perspective of the hydrologic water balance. It aims to determine the spatial extent of wet ground areas and to provide operational guidance through the development of a model that can predict where wet ground may occur at the stand and watershed level. The watershed-level prediction described here will be based on risk indicators developed from available geographic information system data and aerial photographs, as well as local knowledge. Predictions will be qualified through field verification studies at representative stands within ranked watersheds. Preliminary results are presented.