Treasure, Theresa T.

Tree harvesting alters nutrient cycling and removes nutrients held in biomass, and as a result nutrient availability may be reduced, particularly in naturally oligotrophic ecosystems. Selection harvesting is a silvicultural technique limited to tolerant hardwood forests where individual or small groups of trees are removed creating a "gap" in the forest canopy. In order for harvesting machinery to gain access to these individual trees, trees are felled to create pathways, known as skid roads. The objective of this study was to characterize differences in soil chemical and physical properties in gaps, skid roads and uncut areas following selection harvesting in central Ontario as well as documenting differences in the understory vegetation community and sugar maple (Acer saccharum) seedlings chemical composition post harvest. First year seedlings were collected for elemental analysis from unharvested areas, canopy gaps, and skid roads in 2014, eight months after harvesting. In 2015, first and second year sugar maple seedlings were collected. Soil bulk density and water infiltration were measured in the three areas of the catchment as well as soil moisture, organic matter content, exchangeable base cations, and net nitrification. Seedlings in the disturbed sites had lower concentrations of Mg, K, P, and N compared with unharvested sites and soil nitrification was significantly lower in the skid roads. Water infiltration rates in the gap and skid roads were slower than the control and concentrations of metals (e.g. Fe, Al, Ca) and litter mass increased in litter bags deployed over 335 days, likely reflecting an increase in soil erosion in the skid roads. Understory vegetation was markedly different amongst sites, particularly the dominance of Carex spp. in the skid roads. The sustainability of industrial logging is dependent on successful tree regeneration, however, increased soil compaction, establishment and growth of grasses and shrubs, as well as low nutrient concentrations in seedlings may ultimately restrict forest succession.

Author Keywords: Canadian Shield, nitrification, selection harvesting, soil compaction, sugar maple seedling, understory vegetation