Suo - Mires and peat vol. 27 no. 4-5 | 1976

The results of plant coverage analyses carried out in summer 1976 on a peatland drained in 1950 are presented in this article. The results from earlier analyses (1950, -52, -54, -59, -63 and -70) have earlier been published (Mannerkoski 1970). The tree stand characteristics measured in 1961, -66 and -73 are also presented (Table 1). The results for the plant coverage analyses (Table 2, Fig. 2 and 3) have been obtained from five plant coverage sample plots. The tree stand consists mainly of Scots pine and has grown well. The mean stand increment during the period 1966—73 was 5.8 (A26) and 4.0 (A28) m3/ha/yr calculated as the difference between the volumes with bark. There was a lot of Norway spruce and birch seedlings growing in the stand but only few pine seedlings were found (Fig. 1). The most important changes which had taken place in the coverage of different plant species since 1970 were as follows: Dicranum had increased and Sphagnum recurvum had decreased on plots 1—3, Sphagnum robustum had increased on plots 3 and 4 and Vaccinium oxycoccos had decreased on all the plots. Aulacomnium palustre, Eriophorum vaginatum and Carex canescens had completely died out. It can be clearly seen from figures 2 and 3 that the increase in Vaccinium vitisidaea has stabilised and that Polytrichum commune is still present in large numbers. It appears that the changes in the coverage of different plant species are dependant on the effect of shading and competition by the tree stand. Only those species with the greatest moisture requirements have disappeared within the first few years after draining as a result of drying out of the surface peat (cf. Mannerkoski 1970).

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

This paper presents the results of heavy metal (trace element) analyses of plant samples collected from three undrained ombrotrophic bogs in southern Finland (60—61°N, Fig. 1). The species studied included three mosses — Sphagnum fuscum, S. balticum, S. majus — and four lichens — Cladonia stellaris (= C. alpestris), C. arbuscula, C. rangiferina, Hypogymnia (= Parmelia) physodes. Also the needles of stunted bog pines Pinus silvestris) were collected and separated according to age (current vs. 1—2-year-old needles). Collective samples (5—10 replicates) consisting only of the living top part were taken (lichens 4—5 cm, hollow mosses 3—6 cm, hummock mosses 2 cm). The samples were dry-ashed at + 500° C, then dissolved with cone, hydrochloric acid, diluted with distilled water and analysed for metals with Varian Techtron AA-1200 atomic absorption spectrophotometer at Botany Dept., University of Helsinki. Duplicate samples were also digested directly with HNO3 and HCl for control. The results of the former method are presented in Figs. 2—4 on oven-dry ( + 70°C) weight basis. Among bryophytes, the contents of Pb, Zn and Mn were in all cases highest in hummock species Sphagnum fuscum and lowest in the wet-hollow species S. majus. Among lichen species, the concentrations of lead and zinc decrease in the order: Hypogymnia physodes (epiphyte) > Cladonia rangiferina > C. stellaris, C. arbuscula. In Pinus the needles from the current year contain less metals than the needles from previous years. A comparison of different plant groups depends upon the element analysed (see Figs. 2—4). Mn content is highest in pine needles followed by Sphagnum fuscum and lowest in lichens and hollow mosses. Zn content is greatest in the epiphytic lichen Hypogymnia followed by pine needles, then by bog mosses and reindeer lichens. As opposed to zinc, the content of lead is lowest in pine needles which fact suggests a low absorption capacity of atmospheric heavy metals by pine needles. On the other hand, zinc and manganese seem to be actively translocated by pine. Consequently, needle analysis does not appear to be an appropriate method for monitoring the deposition of heavy metals. Both lichens and mosses (with the exception of hollow species), however, seem to be efficient accumulators of zinc and lead at least. If the annual primary production of mosses can be determined, it becomes possible also to estimate the deposition rate per surface area of some heavy metals.

• Pakarinen, Sähköposti: ei.tietoa@nn.oo
• Mäkinen, Sähköposti: ei.tietoa@nn.oo