Suo - Mires and peat 56 (2005)

In this study the vegetation composition of a drained mire that was partly forested and partly kept treeless was compared. The study site was a low sedge fen near the town Oulu in west central Finland. Drainage was carried out in the 1930s. A power transmission line was drawn through the fen in 1956. The area under the line was kept treeless through repeated cleanings. In summer 2004 the vegetation was inventoried on a study area half of which was on the treeless and half on the forested part. The forested and treeless parts were similar with respect to mire site type, depth of peat layer and efficiency of drainage. Therefore the effect of the tree stand on the vegetation on the forested part was obvious. The secondary succession of the vegetation had been significantly slower on the treeless part. Practically no forest moss species, but also fewer Sphagnum moss species were found on the treeless part. On the other hand, a number of sedge-like plants were found only there. With regard to species number and coverage, the largest group was dwarf shrubs, especially on the forested part.

• Silfverberg, Metsäntutkimuslaitos, Vantaan toimintayksikkö (Finnish Forest Research Institute, P.O. Box 18) PL 18, FIN- 01301 Vantaa, Finland Sähköposti: ei.tietoa@nn.oo
• Seväkivi, Sähköposti: ei.tietoa@nn.oo

Understanding the taphonomy of tephra (volcanic ash) is crucial to the use of tephrochronology in peatlands. This study uses field experiments on a Scottish peatland to investigate the post-depositional movement of tephra in peat. Experiments were designed to investigate the temporal change in tephra profiles over a 24-month study period, the horizontal distribution of tephra and the microscopic distribution of tephra particles within the peat. Tephra concentration profiles show that the majority of tephra shards are retained within the top cm of peat with small numbers penetrating to a maximum of 6 cm depth. This distribution would be reduced as the peat is compressed with subsequent accumulation. Examination of thin sections from the plots indicates that tephra movement may be dependent on the microscopic structure of the peat, especially porosity. These results provide general support to the use of tephrochronology although further work will be required, particularly in other peat types and environments.

• Payne, Department of Geography, Queen May, University of London, Mile End Road, London E1 4NS United Kingdom Sähköposti: ei.tietoa@nn.oo
• Kilfeather, Sähköposti: ei.tietoa@nn.oo
• van, Sähköposti: ei.tietoa@nn.oo
• Blackford, Sähköposti: ei.tietoa@nn.oo

Phosphorus and potassium deficiencies are common in Scots pine stands growing on drained peatlands. In this study, the foliar nutrient concentrations and stand growth were monitored after the application of phosphorus and potassium fertilisers of different solubility in four experiments on thick-peated drained peatlands in northern central Finland. The studied stands involved three fertilisation treatments: (i) unfertilised control, (ii) rock phosphate and potassium chloride, and (iii) apatite and biotite. The growth of stands was monitored 20–25 years after the fertilisation. Needles were sampled four times: 4–9, 11–14, 16–19 and 21–24 years after the fertilisation. According to foliar analyses, the trees on the control plots suffered from severe phosphorus and potassium deficiencies. Rock phosphate and apatite fertilisation increased the foliar phosphorus concentrations above the deficiency limit, and the effect was still noticeable 21–24 years after the application. Both potassium sources, that is, the slowly soluble biotite and the water-soluble potassium chloride increased the foliar potassium concentration to an adequate level. Potassium chloride increased the concentrations faster and stronger than biotite during the first years (4–9) after the applications. The situation was reversed when 11–14 years or more had passed from the fertilisation: the biotite fertilised stands had higher potassium concentrations. The fertilisation treatments decreased the foliar nitrogen, zinc, manganese, copper and boron concentrations. The fertiliser applications increased the stand volume growth considerably. Raw phosphate and potassium chloride increased the volume growth significantly already during the first five-year period. The effect of the apatite and biotite treatment was weaker during the first 10 years, but became stronger with time. During the period 19–24 years after the fertilisation, the stand growth on the biotite plots was equal to that of the plots fertilised with potassium chloride. However, during the whole study period the differences between the treatments remained insignificant. The results showed that slowly soluble apatite and biotite are suitable sources of phosphorus and potassium for pines on drained peatlands. However, to avoid boron deficiency, also boron should be added simultaneously.

• Moilanen, Finnish Forest Research Institute, Muhos Research Station, Kirkkosaarentie 7, FIN-91500 Muhos, Finland Sähköposti: ei.tietoa@nn.oo
• Pietiläinen, Sähköposti: ei.tietoa@nn.oo
• Issakainen, Sähköposti: ei.tietoa@nn.oo

The effects of potassium (K) fertilisation on the nutrient status and growth of Scots pine (Pinus sylvestris L.) stands on drained peatlands were studied on three field experiments in northern central Finland. The Scots pine stands were at a sapling or pole stage with a dominant height of 3–8 m when the experiments were set up. The stands differed from each other in their nutritional status, for example, the foliar K concentration varied considerably between the experiments. The experiments were fertilised with potassium chloride, rock phosphate (P 42kg ha-1) and urea (N 46kg ha-1) between 1979 and 1980. The potassium doses in terms of elemental K, were 50, 100, 200 and 400kg ha-1. The foliar samples were taken three times during the study period: 7–9 years, 14–15 years and 19–20 years after fertilisation. The stand measurements were done 19–22 years after the fertilisation. The rate and magnitude of stand response due to fertilisation depended essentially on the nutritional status of the trees. The strongest effect of PK-fertilisation was obtained on a nitrogen-rich peatland, where the stands suffered from severe phosphorus and potassium deficiencies (foliar P concentration < 1.2 mg g-1, K concentration < 3.5 mg g-1). During the study period, the annual stand volume growth on fertilised plots ranged from 3.9 to 5.4 m3 ha-1 a-1, and that of the unfertilised plots was 0.78 m3 ha-1 a-1. In other sites, where the lack of phosphorus and potassium was not so drastic, nor did the trees suffer from shortage of nitrogen, the effect of PK-treatment on tree growth was weak or almost non-existent. The foliar K concentrations rose with the amount of potassium chloride applied. The fertilisation effect of the dose of 100kg K ha-1 lasted 15–20 years, after which the foliar K concentration dropped close to the deficiency limit. The effect of the larger doses (200–400kg K ha-1) on the needle K concentration was more pronounced and still visible at the end of the study period. However, the stand growth responses gained with larger potassium applications were not essentially greater than those with the 100 kg ha-1 dose.

• Pietiläinen, Finnish Forest Research Institute, Muhos Research Station, Kirkkosaarentie 7, FIN-91500 Muhos, Finland Sähköposti: ei.tietoa@nn.oo
• Moilanen, Sähköposti: ei.tietoa@nn.oo
• Vesala, Sähköposti: ei.tietoa@nn.oo

Water table measurements were obtained in a treed fen that was drained in 1987 and harvested for timber in 1997. The water table level was quantified at five different distances from the ditch for three ditch spacing. Water table levels were compared between pre-drainage, post-drainage and post-removal of the canopy. The phenomenon of watering-up after clear-cutting did not occur where a drawdown of at least 10 cm was caused by the drainage. This lowering was observed across the 20 m ditch spacing and within the first 6 m from the ditch, in the 40 and the 60 m spacing. The water table fluctuations were also reduced after harvesting.

• Jutras, Forest Biology Research Centre, Université Laval, Sainte-Foy, QC G1K7P4 Canada Sähköposti: ei.tietoa@nn.oo
• Plamondon, Sähköposti: ei.tietoa@nn.oo

The study deals with the dimensions and condition of ditches five and ten years after ditch network maintenance in southwest Finland. The deterioration of ditches was very fast, averaging 20 cm five years and 30 cm ten years after ditch network maintenance. The shallowing of the ditches depended on the type of soil at the bottom of the ditch. There are several factors related to the deterioration of ditch condition, including: falling stones and erosion just after digging, moose paths, growth of vegetation in ditches and litterfall, clogging of culverts and shallow main ditches and unevenness of ditch bottom. The growth of vegetation in ditch bottoms is rapid and vigorous. Vegetation cover in the ditch bottoms averaged 68% five years and 100% ten years after ditch network maintenance. Our results indicate that about 25% of the ditches in southwest Finland should be cleaned again during the rotation period. We recommend the drainage ditches be re-dug to 0.9–1.1 m depth and that the main ditches be dug 20–30 cm deeper. In this way it should be possible to reduce the number of ditch maintenance operations needed at a site.

• Silver, Lounais-Suomen metsäkeskus (Lounais-Suomi Forestry Centre) Kuralankatu 2 FIN-20540 Turku, Finland Sähköposti: ei.tietoa@nn.oo
• Joensuu, Sähköposti: ei.tietoa@nn.oo

In Finland, the whole peat layer of a peat production area is used due to the value of the basal peat as energy peat. In this situation the properties of the mineral subsoil below the peat layer are significant when choosing the form of after-use. The geochemical provinces are based on the chemical features of the fine material in till, related to differences found in the bedrock, defined by Geological Survey of Finland. The study of peat production areas (1998-1999, covering 9800 ha) shows that the characteristics of the provinces affects the subsoil sediments. In Lake Ladoga–Bothnian Bay zone subsoils were rich in sulphur and iron. The amount of water soluble sulphur was 3-6 times higher than that in the Granitoid area of Central Finland and the Archaean gneiss areas (calculated as mg kg-1). Below the highest shoreline of the ancient Litorina Sea the average content of the water soluble sulphur in subsoil sediments was ca. seven fold compared to the content found above the highest shoreline, (calculated as mg kg-1). There was also a difference in soil acidity between these areas. Nutrient content varied between sediments, which have the same fine material percentage. In the Lake Ladoga–Bothnian Bay geological zone and in the zones of Svecocarelian schists and gneisses, natural nutrient levels are high when compared to the Granitoid areas.

• Picken, Kekkilä Oyj, P.O. Box 67, 04300 Tuusula, Finland Sähköposti: ei.tietoa@nn.oo

Peat hydraulic conductivity (K), specific yield (S), degree of humification and shear strength were measured at two wetland treatment systems constructed on natural peatlands receiving different wastewater quality and loading in Northern Finland. Peat K was measured with a falling head piezometer test in situ and by taking soil cores in horizontal and vertical directions using Eijkelkamp cylinders. Peat S was obtained from pF-curves and drainage tests. The K in situ was 5.2x10-7 - 2.9x10-3m s-1, the horizontal K was 6.1x10-6 - 3.8x10-2 m s-1 and the vertical K was 4.2x10-6 - 2.6x10-2m s-1. The highest K value was usually found in the vertical direction. The estimated acrotelm layer with high K reached 40 - 60 cm at Kompsasuo wetland and 10 - 60cm at Ruka wetland. There was an agreement between different measurement methods for S when pF values corresponding to relevant negative pressure were used. S varied from 0.023 to 0.23. After several years of wastewater loading, the peat hydraulic conductivity was still sufficient to maintain wastewater flow in the top 50 cm of the peatland.

• Ronkanen, Sähköposti: ei.tietoa@nn.oo
• Kløve, Sähköposti: ei.tietoa@nn.oo

The present paper introduces and describes a poorly known wetland type – aro wetland – in well permeable mineral soil substratum in Northern Ostrobothnia and Kainuu (between 64° – 66° N lat.). Field observations (linked with the interpretation of aerial photographs) were made in 32 localities, whose conservation status is presented. We define boreal aro wetlands ecologically as a seasonal wetland type of their own which occur on well-drained mineral soil, which are mainly characterised by treeless, mire expanse fen vegetation and in which the peat accumulation is (almost) totally hampered by the vigorous decomposition of the organic matter resulting from an extremely unstable water regime (flood and seasonal drought) and small plant production. Aro wetlands in the western part of the study area occur on sandy substratum (the largest in parts of mire complexes split by ancient raised beach ridges), whereas in the eastern part the aro wetlands known so far are small pond-like depressions in till substratum. Carex lasiocarpa (mostly) dominates the vegetation on sandy substratum. Juncus filiformis and Carex nigra are typical, and Rhynchospora fusca and Molinia caerulea a bit rarer. Sphagnum cover is usually minimal. Considering aro wetlands an extreme case of suo (mire) makes the stability of water regime (stable – unstable) a direction of variation in the traditional Finnish mire site type system, which is based on several ecological gradients.

• Laitinen, University of Oulu, Department of Biology, Botany, P.O.Box 3000, FI-90014, Finland Sähköposti: ei.tietoa@nn.oo
• Rehell, Sähköposti: ei.tietoa@nn.oo
• Huttunen, Sähköposti: ei.tietoa@nn.oo
• Eurola, Sähköposti: ei.tietoa@nn.oo