Suo - Mires and peat vol. 27 no. 1 | 1976

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.

• Pelkonen, Sähköposti: ei.tietoa@nn.oo

The material used in this study consists of two peat profiles taken from the raised bog at Ylimysneva, Parkano, in south-western Finland (Fig. 1). The correlation between the results obtained from various methods of determining the degree of humification was calculated. The methods used included the humification scale according to von Post (1922), the colon-metric method of Kaila (1956), the bulk density measurements (Päivänen 1969) and the fiber content estimation of Sneddon, et. al. (1971). The negative correlation found between the humification scale according to von Post and the fiber content proved to be statistically highly significant (Fig. 2 and 3). There was a highly significant negative correlation between the fiber content and the bulk density in the case of profile II (Fig. 5) and significant negative correlation with respect to profile I (Fig. 4). The results showed that the fiber content seems to be well suited for measuring the degree of humification. The correlations found between the colorimetric method of Kaila and the other methods were relatively weak (Table 1). This is partly due to the fact that the method is not suitable for use with all the different types of peat. The correlations which were found between the humification degree according to von Post and figures for the bulk density were lower than those reported in the literature. This is very likely caused by layers of charcoal and alluvial material in the peat.

• Raitio, Sähköposti: ei.tietoa@nn.oo
• Huttunen, Sähköposti: ei.tietoa@nn.oo

In the paper, a preliminary model of the structure and function of a boreal mire ecosystem is presented. In addition, a research plan leading to the model is described. In the exploitation and management of natural resources, information about the ecosystem as a functional unit is needed, if ecological principles are to be applied. In Finland, mires (peatland ecosystems) have been subject to exceptionally severe exploitation since forest drainage and fertilization effectively started in the 1960's, However, mires represent one of the least known ecosystems. The mire ecosystem has been defined according to Ellenberg's (1973) criteria as follows. A mire is an ecosystem maintained by cool and humid local climatic conditions and a high water table, which results in deficient decomposer activity and accumulation of organic matter (peat-forming process). The most striking features in the energetics of the system are a relatively ineffective input of energy and an even more ineffective use of it. This is indicated in the metabolism of the system by an excess production of oxygen and, in addition, by losses in the carbon, mineral, and nitrogen cycles. A general model of the mire ecosystem is presented in Figure 1, which simultaneously serves as a framework for the study. The individual parts of the project are planned to be as follows: (1) environmental factors, (2) plant community and primary production, (3) secondary production, in which (3a) energy flows through herbivores, and (3b) energy flows through decomposers, (4) nutrient cycle, (5) the accumulation of peat, and (6) succession in the mire ecosystem. In (1), special attention has been paid to factors characteristic of mires, especially the factors connected with the water table. As the aim of the study is to obtain a dynamic model of a biotic phenomenon, emphasis has been put on the continuous observation of environmental factors. In (2), a graphic model (Fig. 3) has been chosen as the primary goal. Graphic models of a few peatland site types based on preliminary studies already exist. When constructing dynamic ecosystem models, the growth rhythm of the plant communities is the most important study object. Some advances in the methodological development of measuring the growth of mire plants have been achieved. For instance, the problems involved in measuring the height growth of Sphagnum mosses in field conditions have partly been solved. An application of the IRGA-technique to studying the organic matter production of the Sphagnum — dwarf shrub community is ready for use in field conditions, but the methods for combining direct measurement data with IRGA results are still inadequate. The main task in (3) is characterized by Figure 2, i.e. energy flow and material should be divided into biotic components. By using population studies, decomposition tests, and experimental respiration techniques, a more detailed quantitative model of these pathways can be constructed. Preliminary results for total decomposer activity and the role of soil animals in detritus energy flow have already been revealed. Branches (4) and (5) are very closely connected with each other and with (3b). A detailed study into the different terms which make up the accumulation equations as a function of the environmental factors has been proposed. In (6), the suitability of the mire ecosystem as a study object of stability and succession problems has been emphasized. The successio-nal stage of the ecosystem is very strongly affected by forest improvement measures. For this reason, the study of the regulation mechanisms of mire communities is important in Finland, where about 4.5 mill. ha. out of a total of 10 mill. ha. have been drained and partly fertilized so far for forestry purposes. Finally, the future of the planned research project The structure and function of mire ecosystems and the effects of forest improvement on them is discussed. The working group consisting of biologists from the Finnish Forest Research Institute (Department of Peatland Forestry) and from a number of departments at Helsinki University (Botany, Zoology, Microbiology) is waiting for the research plan, now connected with the MAB-program of Finland, to be financed. The preliminary studies are continuing on a small scale.

• Reinikainen, Sähköposti: ei.tietoa@nn.oo

The insect fauna of Finnish peatlands is considered from the ecological point of view. The article is based on the literature published in Finland and on the author's own observations on the lepidopterous fauna of peatlands. Insects play an important role in peatland ecosystems. Several families of Diptera, e.g. Culicidae, Chironomidae, Tipulidae and Tabanidae make large contributions to the total biomasses. Dipterous insects constitute the chief food source of many waders, passerines and other birds. It is suggested that peatlands would be devoid of birds if there were no insects. The characteristic microclimate of peatlands is supposed to produce a complex of ecological factors which often determines the habitat selection and geographical range of different species. In pine bogs the temperature variations are very great as a result of the weak thermal conductivity of the Sphagnum moss layer. The most extensive temperature variations occur in relatively dry pine bogs (a "continental" climate) and the least variations in fens containing large volumes of water (a "maritime"" climate). Moisture and acidity (pH) of the moss layer are other ecological factors considered. The lepidopterous fauna is richest on pine bogs. A list is given of the most typical butterfly and moth species found on peatlands and an attempt has been made to assign the species to different peatland types, r = on pine bogs, n = on open bogs, l = on fens, k = on spruce swamps, + = on other biotopes, too, N = mostly or exclusively in Northern Finland and S = only in Southern Finland. It is stressed that the draining of peatlands has a very serious effect on the insect fauna owing to their high sensitivity to change in the microclimatic conditions. "

• Mikkola, Sähköposti: ei.tietoa@nn.oo