Current issue: 54(5)
Under compilation: 55(1)
The winter 1986–87 was unusually cold; the snow cover remained thin and consequently the soil froze to a considerable depth. In spite of the severe frost, the lowest temperatures measured at the ground surface was -10.3°C and in the soil at the depth of 10 cm -5.8°C. The temperature sum of the following summer was unusually small and the soil frost melted more slowly than usual. The winter frosts did not have a decisive influence on the survival of planted seedlings.
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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.
The PDF includes a summary in Finnish.
The purpose of this paper was to determine the proportions of nutrients remaining in the forest and removed from the forest as a result of cutting. The Norway spruce (Picea abies (L.) H. Karst.) phytomass remaining after clear cutting was studied in the categories of tree-top waste, branches, twigs, needles and cones. The bole wood, measured in solid cubic metres, was converted to kilogrammes on the basis of relative density determinations, and the amount of stump and root material estimated from the known amount of bole wood and comparable data presented in the literature. The nutrients studied were N (Kjeldahl), P (colour reaction), K, Ca, Mg, Fe and Mn (atomic absorption spectrophotometer). The wood and bark were studied separately. Details of the mineral composition of the bedrock are also presented.
The harvested timber was found to account for 46 % of the total phytomass, or 58 % of the aerial phytomass, while the stump and root material represented one fifth of the total phytomass. The needles and bark contained the highest proportions of nutrients, especially in the case of nitrogen and phosphorus, the needles containing 32 % of total nitrogen and 26 % of total phosphorus. The surface waste wood contained on average more than double the amount of nutrients compared with the harvested bole wood, including more than six times the amount of phosphorus. Approximately one fifth of the nutrient contained in the total phytomass was removed on cutting. The high proportion of basic rocks in the area is suggested as an explanation of the nutrient status at the site, which is in many ways better than that described in the results of other investigations.
The PDF includes a summary in Finnish.