Current issue: 57(1)
Under compilation: 57(2)
The effect of scarification, ploughing and cross-directional ploughing on temperature conditions in the soil and adjacent air layer have been studied during 11 growth periods by using an unprepared clear-cut area as a control site. The development of seedling stand was followed to determine its shading effect on the soil surface.
Soil preparation decreased the daily temperature amplitude of the air at the height of 10 cm. The maximum temperatures on sunny days were lower in the tilts of the ploughed and in the humps of the cross-directional ploughed sites compared with the unprepared area. Correspondingly, the night temperatures were higher and so the soil preparation reduced the risk of night frost. In the soil at the depth of 5 cm, soil preparation increased daytime temperatures and reduced night temperatures compared with unprepared area. The maximum increase in monthly mean temperatures was almost 5°C, and the daily variation in the surface parts of the tilts and humps increased so that excessively high temperatures for the optimal growth of the root systems were measured from time to time. The temperature also rose at the depths of 50 and 100 cm.
Soil preparation also increased the cumulative temperature sum. The highest sums accumulated during the summer months were recorded at the depth of 5 cm in the humps of cross-directional ploughed area (1,127 dd.) and in the tilts of the ploughed area (1,106 dd.), while the corresponding figure in the unprepared soil was 718 dd. At the height of 10 cm the highest temperature sum was 1,020 dd. in the hump, and 925 dd. in the unprepared area.
The incidence of high temperature amplitudes and frequency of high temperatures at the depth of 5 cm decreased most rapidly in the humps of cross-sectional ploughed area and the ploughing tilts towards the end of the study period. The decrease was attributed principally to the compressing of tilts, the ground vegetation succession and the growth of seedlings. The difference between the prepared and unprepared area did not diminish. The increase in temperature due to soil preparation, thus, lasted at least over 10 years.
The present paper deals with the effects of clearcutting on soil and air temperature and the development of temperature conditions during the 12 growing seasons following clearcutting of a Norway spruce (Picea abies (L.) H. Karst.) stand on a Vaccinium-Myrtillus forest type in Kainuu, northeast Finland. The uncut control site had a growing stock of 140 m3/ha. The temperature measurements were carried out by means of thermographs, Grant measuring devices and minimum and maximum glass thermometers.
Clearcutting had no significant influence on temperatures measures at 2 m above the ground in a meteorological screen and no changes occurred in them during the period studied, while on the ground level and in the adjacent layer of air the daily maxima increased and the daily minima decreased as compared with uncut forest. The greatest difference was over 10°C between the maximum temperatures at 10 cm and almost 8°C between the minimum temperatures. Night frosts were considerably more common at 10 cm above the ground in the clearcut area than in uncut forests.
Temperature differences were smaller in the soil than close to ground level. Day temperatures were 2–3°C higher in the clearcut area than in uncut forests, and differences between night temperatures at this depth were even smaller. Correspondingly, temperatures were 3–5°C higher at depths of 50 cm and 100 cm in the clearcut area during the whole measuring period. The differences between the temperatures in the clearcut area and uncut forests did not diminish to any significant extent during the 12 years despite the stocking of the former area with seedlings.
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