TEMPERATURE-VARIATIONS IN PLANTING MOUNDS DURING WINTER

Soil temperatures were measured at a depth of 8 cm in top, middle, and bottom positions of 30 cm high mineral and organic mounds and at 8 cm depth in scarified patches during winter and spring 1987-1988 and 198 8-1989. At low air temperature, frozen mounds without snow cover showe d much lower temperatures than snow-covered mounds, the maximum differ ence being 16 degrees C. During the coldest period of the two winters, when minimum air temperature was -26 degrees C, soil temperature in t he top of a snowless mineral mound remained within -16 to -10 degrees C for 3.5 days and -8 to -5 degrees C in a snowless scarified patch. M inimum temperatures were lower, duration of low temperature freezing w as longer, and temperature changes were more rapid in mineral than in organic mounds. Large temperature differences were found between the t op and the bottom of mounds. In dry conditions during early spring, th e upper part of the mineral mound thawed and froze repeatedly with dai ly maximum and minimum temperatures of 5 degrees C and -6 degrees C. S oil temperature patterns during the winter period are discussed in rel ation to root freezing tolerance of conifer seedlings. Mounding as a s carification method should be used with care as winter temperatures ma y injure seedling root systems.