Suo - Mires and peat vol. 47 no. 4 | 1996

The structure of peatland forests were compared between different site quality classes, drainage phases, and different forest ownership groups. The comparisons and statistical tests were made in terms of the number of tree species, range of diameter distribution and the estimated number of tree storeys, separately for spruce- and pine-dominated mires. The statistical tests were performed with multivariate analysis of variance and covariance. Tree storeys were estimated with objective rules from the peaks of continuous diameter distribution smoothed by the non-parametric kernel-estimation. The data used from the 8th National Forest Inventory of Finland. On average the mean values of the chosen stand structure characteristics differed significantly between the site quality classes. The stands had a more diverse structure the more fertile the site was. When examining the differences between the post-drainage succession phases, a decrease of the stand structure diversity was observed in the recently drained peatlands. After this, the mean values of the stand structure characteristics increased and exceeded the values of undrained peatlands at latest in the transformed post-drainage succession stage. Statistically significant differences in the means of stand structure characteristics between the forest ownership groups were not observed. It seems that drainage and possible cleaning cuttings have been made with the same intensity regardless of the particular forest ownership group. It is also possible that drainage causes so drastic change in growing conditions that small differences in the intensity of cleaning cuttings between forest ownership groups are disappeared. The results correspond to the results of previous studies which have examined different stand structure characteristics. The forest on drained peatlands maintains an uneven-sized structure for quite a long period after drainage. In order to preserve habitat diversity this structure of the peatland forests should be maintained in subsequent forest management practices. Key words: drainage, habitat diversity, peatland forest management, structure of forest stand.

• Uuttera, The European Forest Institute, Torikatu 34, FIN-80100 Joensuu, Finland Sähköposti: ei.tietoa@nn.oo
• Maltamo, Sähköposti: ei.tietoa@nn.oo
• Hotanen, Sähköposti: ei.tietoa@nn.oo

Four excavators were studied in site preparation in different excavation difficulty classes (1-3) during the unfrozen period in the central and the northern Ostrobothnia in western Finland. In mounding the mean productivity (per effective hour) of the excavators was 0.17 ha h-1 and in scarification 0.32 ha h-1, respectively. The work quality was acceptable. In mounding and scarification, the mean number of planting positions was about 3600 per hectare. The mean height of the mound was about 28 cm, the mean dimensions of the scarified surface being 330 cm x 75 cm. The operation costs were 268-388 FIM per hour, if the price of the excavator was 400 000-1000 000 FIM. Key words: excavator, mounding, scarification, work studies.

• Lauhanen, The Finnish Forest Research Institute, Kannus Research Station, FIN-69100 Kannus, Finland Sähköposti: ei.tietoa@nn.oo

In north-east Estonia the precipitation of calcium-rich strongly alkaline fly ash from thermal power stations has caused significant changes in the local ombrotrophic mires. Sphagnum mosses disappeared from Niinsaare bog during the 1970s in the period of the highest air pollution. Their disappearance was probably caused mainly by the combination of high pH values and an increased concentration of calcium in the bog water. In Niinsaare bog, the present mean pH value of bog water is 5.3 ± 0.6 and the mean calcium concentration 11.6 ± 1.6 mg l-1, compared with 3.7 ± 0.4 and 1.9 ± 0.2 mg l-1 in the uncontaminated Nigula bog respectively. During the last decade, following the reduction of fly ash emission, the Sphagnum mosses started to reappear in Niinsaare bog. Nine Sphagnum patches dominated mainly by S. angustifolium, S. fallax and S. magellanicum were studied from June 1991 to September 1995. During one year, the distance between the centre and edges of these patches increased on an average by 5.1 ± 2.7 cm and the area by 29 ± 21.5 %. This indicates that the degeneration of Sphagna in NE Estonian bogs is not yet irreversible and, by reducing the air pollution in long term, the restoration of Sphagnum carpet is possible. Key words: atmospheric pollution, degeneration and recurrence of Sphagna, ombrotrophic mire.

• Karofeld, Institute of Ecology, Kevade Str. 2, EE0001 Tallinn, Estonia Sähköposti: ei.tietoa@nn.oo