INTENSIVE HARVESTING IMPACTS ON SOIL TEMPERATURE AND SOLUTION CHEMISTRY IN THE MARITIMES REGION OF CANADA

Starting in 1989, a series of lysimeter studies was initiated to evaluate the potential impacts of different harvesting and site preparation methods on site quality. Experiments were laid out in the field on soil types representative of the land base supporting the growth of all the major commercially important tree species in the Maritimes region. Although different treatments applicable to local situations were implemented on each site, three treatments included on all sites were: control (no harvest), conventional stem harvest (boles only) with slash left on site, and whole-tree harvest (all biomass above the stump removed from the site. On all study sites, soil temperature was monitored hourly (1) immediately below the organic horizons, (2) mid-way between the surface and the bottom of the rooting zone, and (3) below the rooting zone. Hourly mean temperatures in the top (immediately below the organic) horizon clearly exhibited effects of harvesting methods. In the whole-tree harvest plots, during June-August, the hourly mean temperature was 6-8 °C warmer than that in the conventional harvest plots. Also, temperature peaked about 2 h later in the whole-tree harvest plots than in the conventional-harvest plots. Similar trends were consistently recognisable at lower depths as well, indicating that whole-tree harvesting has the potential to enhance weathering in the subsoil. The treatment effects were equally distinguishable in the values for daily mean temperature, except in the early spring and later summer (late August) when the daily mean temperature was higher in the conventional-harvest plots than in the whole-tree harvest areas owing to the insulating effect of slash. The accumulated heat units (cumulative number of hours times the soil temperature above 5°C) were greatest in the whole-tree harvest areas, followed by the conventional-harvest and then the control plots