Current issue: 53(2)
Under compilation: 53(3)
Hybrid aspen (Populus tremula L. × P. tremuloides Michx.) is a deciduous tree species suitable for producing large amounts of renewable biomass during short rotations. Its potential under North European conditions could be largely extended if not only agricultural land but also forest land was used for cultivation. Unfortunately, the knowledge of appropriate forest site conditions and effects of site preparation methods on hybrid aspen establishment is limited. In this paper, two studies that explore these questions are presented. In the first study, the sensitivity to acid soils was tested under greenhouse conditions in two type of soils: a) peat soil limed to certain pH levels (3.4–5.7) and b) collected forest soils where pH varied from 3.9 to 5.3. The lowest pH level resulted in reduced growth, elsewhere no significant differences were found. The second study was applied in the field and investigated the effect of four site preparation methods on survival and growth. The methods were: 1) control with no site preparation, 2) patch scarification, 3) mounding and 4) soil inversion. While no differences were found for survival, mounding was generally the method with the highest growth and patch scarification was least successful. The result was probably an effect of good soil aeration and less competition from vegetation after mounding. The field study also revealed clonal differences in growth performance, which stresses the importance of clone selection prior to planting. The results of these studies indicate that hybrid aspen is less sensitive to variation in pH and site preparation methods compared with other poplar species, as have been found in similar studies.
To promote the growth and survival of regenerated forests, site preparation prior to tree planting on clearcuts is necessary. This is often performed with scarifiers, either through trenching or mounding. Mounding is generally considered better in a plant survival perspective but is inefficient on obstacle-rich clearcuts. By utilising machine vision through e.g. remote sensing methods, new strategies can enable efficient mound positioning. In this paper, three realistic strategies utilizing ideal clearcut object identification through machine vision have been developed that can be used for more efficient mounding. The results show that mounding efficiency can be significantly improved with a new mound positioning strategy that employs ideal object identification, especially on obstacle-rich clearcuts.
Five ploughed research areas from Finnish Norther Karelia were selected for comparison studies of plough ridges and untouched soil. Measurements were made at a depth of 10 cm in sample plots on both mineral and paludified mineral soil and peatland parts of these areas. In summer 1987 daily soil water matric potential was measured using tensiometers, and volumetric soil moisture content and density were determined from soil samples at two dates during the summer. Water characteristics of the core samples were also determined. On paludified mineral and peat soils the water table depth from the soil surface was measured.
The results indicated that in plough ridges matric potential was lowest. Plough ridges were also seen to dry and wet faster and to a greater degree than untouched soils. In untouched soils, soil water relations and aeration were not affected by the distance to the furrow. The effect of the plough ridge was smallest on peatland, where there was a good capillary connection from plough ridge to the ground water, if the ditches were not very effective. The soil in the ridges did not dry too much to restrict seedling growth. The untouched surface soil in poorly drained peat and paludified minear soil was, at least in a rainy growing season, often and also for long times so wet that 10% minimum air space required for good seedling root growth was not available.
The PDF includes an abstract in English.
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.
The PDF includes an abstract in English.