SILVICULTURAL TREATMENTS, MICROCLIMATIC CONDITIONS AND SEEDLING RESPONSE IN SOUTHERN INTERIOR CLEARCUTS

Post-harvest levels of soil disturbance and vegetation regrowth strong ly influence microclimate conditions, and this has important implicati ons for seedling establishment. We examined the effects of blading (sc alping), soil loosening (ripping) and vegetation control (herbicide), as well as no soil disturbance, on growing season microclimates and 3- yr seedling response on two grass-dominated clearcuts at different ele vations in the Southern Interior of British Columbia. Warmer soil temp eratures were obtained by removing surface organic horizons. Ripping p roduced somewhat higher soil temperatures than scalping at the drier, lower-elevation site, but slightly reduced soil temperatures at the we tter, higher-elevation site. Near-surface air temperatures were more e xtreme (higher daily maximums and lower daily minimums) over the contr ol than over exposed mineral soil. Root zone soil moisture deficits la rgely reflected transpiration by competing vegetation; vegetation remo val was effective in improving soil moisture availability at the lower elevation site, but unnecessary from this perspective at the higher e levation site. The exposed mineral surfaces self-mulched and conserved soil moisture after an initial period of high evaporation. Ripping an d scalping resulted in somewhat lower near-surface available soil wate r storage capacities. Seedling establishment on both clearcuts was bet ter following treatments which removed vegetation and surface organic horizons and thus enhanced microclimatic conditions, despite reducing nutrient supply. Such treatments may, however, compromise subsequent s tand development through negative impacts on site nutrition. Temporal changes in the relative importance of different physical (microclimate ) and chemical (soil nutrition) properties to soil processes and plant growth need to be considered when evaluating site productivity.