Eero Pelkonen

Valunnan säännöstelyn tarpeellisuudesta metsäojitusalueella

Pelkonen E. Valunnan säännöstelyn tarpeellisuudesta metsäojitusalueella.

English title: The need for runoff regulation on peatlands drained for forestry

Tiivistelmä

According to results presented previously by the author (Pelkonen 1975), a high water table during the late summer and fall has a harmful effect on tree growth on peatlands drained for forestry purposes. No harmful effect seemed to be involved, when the water table was maintained close to the soil surface in spring and early summer. In this paper, more data is presented on the influence on tree growth of a high water table in spring and early summer. In addition, some points concerning practical runoff regulation are discussed. In two stands the water table was artificially maintained close to the soil surface for varying periods in the course of four summers (1972— 1975). In the pine stand, an increase in circumference growth was recorded irrespective of treatment duration (Fig. 4). However, the increase was the greater, the longer the treatment duration. In 1975, the difference between treatments of different duration became apparent during a prolonged dry period (Fig. 6). In the spruce stand, a significant decrease in growth was recorded in 1973 (Fig. 5). This was obviously due to abundant cone production in the stand during that particular year (c.f. Simpanen 1972). In the case of Norway spruce, circumference growth was not as clearly influenced by treatment duration as was Scots pine. However, even in this case the increase in circumference growth appears to be greatest on the plot with the longest treatment duration. Precipitation, depth of the water table, and cumulative circumference growth in 1975 are presented in Figure 7. It appears that no clear differences have developed between treatments of different duration in the course of the dry spell in July—August. The different response of Scots pine and Norway spruce might be due to site differences. On the basis of this experimental data, it seems probable that tree growth could be stimulated by maintaining the water table close to the soil surface in spring and early summer. In practice, the regulation of runoff from drained areas can easily be carried out by constructing peat dams in the ditches with plastic discharge tubes.

Vastaanotettu 31.10.2017 Julkaistu 1.1.1976

Katselukerrat 410

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