Seasonal changes in soil temperature and snow-cover under different simulated winter conditions: Comparison with frost hardiness of Scots pine (Pinus sylvestris) roots

Abstract

Seasonal changes in soil temperature and in the frost hardiness of the roots of adult Scots pine (Pinus sylvestris L.) trees were studied between August 1992 and May 1993 in a pine forest growing on dry heathland soil. The study area is located in Finnish Lapland (67°N, 29°E). Air (2 m above ground) and soil (5 cm depth of mineral soil) temperatures were measured continuously every second hour. The frost hardiness of the roots in the soil (down to 10 cm) was measured by means of the electrolyte-leakage method. The air temperature remained consistently below 0°C after the first week of October. The coldest month was February with a daily average temperature of −10.3°C. Snow accumulation started in the first week of October and reached a depth of 129 cm in April. The temperature in the mineral soil varied between +15.4°C and 0.8°C. The frost-hardiness of the pine roots was at its lowest in September (−6°C), and at its highest in December (−21°C). Soil temperature and precipitation as snow in different winter conditions were simulated using the SOIL model. The simulations show that the insulating effect of the snow cover is crucial for the frost survival of Scots pine roots even during a moderate winter.