Tapio Lindholm , Harri Vasander

Männyn kasvu ja uudistuminen luonnontilaisella ja ojitetulla sekä lannoitetulla keidasrämeellä

Lindholm T., Vasander H. Männyn kasvu ja uudistuminen luonnontilaisella ja ojitetulla sekä lannoitetulla keidasrämeellä.

Tiivistelmä

The effect of draining and fertilization on the radial and height growth of Scots pine has been studied on an ombrotrophic bog Laaviosuo in the vicinity of Lammi Biological Station. The study site represents a southern Finnish raised bog with Calluna vulgaris — Empetrum nigrum — Sphagnum fuscum -hummocks and Eriophorum vagi-natum — Sphagnum angustifolium or Sphagnum majus — S. balticum -hollows. Total thickness of the peat layer is 5—7 m with a 2—3 m of Sphagnum peat on the surface. Part of the bog (6 ha) was drained in 1966 and fertilized in 1970 (N as urea 100 kg/ha plus PK fertilizer 400 kg/ha). This study is part of a project concerning the comparative analysis of virgin and forest-improved mire ecosystems (Ruuhijärvi et al. 1979). Height growth of pines during 15 last years was measured with the accuracy of 1 cm from 37 trees in the virgin site, 23 trees in the site with only drainage and 27 trees in the drained and fertilized site during the autumns 1978 and 1979. In addition seven trees from a virgin dwarf shrub pine bog near the marginal slope of Laaviosuo were measured for comparison in the autumn 1978. Radial growth was measured in 1979 from 17, 10, 10 and 7 trees, respectively, with the accuracy of 0.01 mm. All the measured trees were selected randomly. At the same time we counted all the trees and seedlings from a sample area both in the virgin and fertilized sites. In the virgin bog the size of the sample area was 1.92 ha and in the fertilized area 1.60 ha for trees and 0.88 ha for seedlings. Height of all seedlings was measured with the accuracy of 10 cm and breast height diameter (d1.3) of trees with the accuracy of 1 cm. Growth of trees in the virgin bog site was very low: height growth about 3 cm and radial growth: 0.2 mm annually (Fig. 1, 2). In dwarf shrub pine bog the corresponding values were about 9 cm and 0.6 mm. Mere draining had very little effect (about 1 cm) on the height growth (Fig. 1.). Radial growth increased more clearly (Fig. 2). However, the figures exaggerate the situation because the trees have been measured very near the ditches (about 1—8 m). Trees which have grown at a distance of less than about 3 m from the ditches have incresed their radial growth, but others growing further away have not. This increases the variation as seen in Fig. 2. In practise, if this kind of ombrotrophic bog is drained fertilization with all macro-nutrient (N, P, K) is needed. Effect of fertilization is very similar on radial and height growth with the difference that height growth always reacts one year later (Fig. 1, 2). Maximum growth (about 35 cm and 3.2 mm) was reached in 1973 and 1974, respectively, after which the growth decreased almost as quickly as it had increased. In ombrotrophic sites the effect of fertilization is known to last less than ten years (Huikari & Paavilainen 1972 and Ipatiev & Paavilainen 1975). Only refertilization could possibly secure the continuing of tree growth. Fertilizing has changed also the size-classes of trees and seedlings (Fig. 5,6). Number of trees has increased from 470 per ha in the virgin area to 1390 per ha in the drained and fertilized area. The tree volume increment has been six-fold (from 1.3 to 8 m3/ha). Number of pine seedlings increased from 7100 per ha to 15300 per ha. There were also 2060 birch seedlings per ha in the fertilized area. Especially hollows have become stocked with seedlings. All these seedlings must compete with dense shrub layer for the nutrients but its effect on the mortality of seedlings can not yet be known. Mere draining seemed to have no effect on the population structure of seedlings. The present volume of the pine stand in the fertilized area, 8 m3/ha on average, is of the same magnitude as Heikurainens (1971) average values for virgin cottongrass pine bogs. However, drainage of cotton-grass pine bogs and Sphagnum fuscum pine bogs with so scarce pine stands seems to be economically questionable (Heikurainen 1973). Thus according to our results, even after the drainage and NPK fertilization the tree stand of this site type is still so low that the drainage and fertilization of such ombrotrophic pine bogs is probably unprofitable.

Vastaanotettu 31.10.2017 Julkaistu 1.1.1979

Katselukerrat 1442

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