Current issue: 54(2)
The carbon reservoir of ecosystems was estimated based on field measurements for forests and peatlands on an area in Finland covering 263,000 km2 and extending about 900 km across the boreal zone from south to north. More than two thirds of the reservoir was in peat, and less than ten per cent in trees. Forest ecosystems growing on mineral soils covering 144,000 km2 contained 10–11 kg C m-2 on an average, including both vegetation (3.4 kg C m-2) and soil (uppermost 75 cm; 7.2 kg C m-2). Mire ecosystems covering 65,000 km2 contained an average of 72 kg C m-2 as peat. For the landscape consisting of peatlands, closed and open forests, and inland water, excluding arable and built-up land, a reservoir of 24.6 kg C m-2 was observed. This includes the peat, forest soil and tree biomass. This is an underestimate of the true total reservoir, because there are additional unknown reservoirs in deep soil, lake sediments, woody debris, and ground vegetation. Geographic distributions of the reservoirs were described, analysed and discussed. The highest reservoir, 35–40 kg C m-2, was observed in sub-regions in central western and north western Finland. Many estimates given for the boreal carbon reservoirs have been higher than those of ours. Either the Finnish environment contains less carbon per unit area than the rest of the boreal zone, or the global boreal reservoir has earlier been overestimated. In order to reduce uncertainties of the global estimates, statistically representative measurements are needed especially on Russian and Canadian peatlands.
Relationships between bulk density and organic matter (OM) content, textural properties and depth are described for forested mineral soils from Central and Northern Finland. Core samples were taken of 0–5, 30–35 and 60–65 cm layers at 75 plots. Three measures of bulk density were calculated: the bulk density of the < 20 mm fraction (BD20), the bulk density of the < 2 mm fraction (BD2), and laboratory bulk density (BDl). BDl was determined from the mass of a fixed volume of < 2 mm soil taken in the laboratory. All three measures of bulk densities were strongly correlated with organic matter content (r ≥ -0.63). Depth and gravel (2–20 mm) content (in the case of BD2) were also important variables. BDl was sensitive to clay contents > 7% but did significantly improve the prediction of both BD2 and BD20 in coarse soils (clay contents ≤ 7%). Predictive models were derived for coarse soils.
Transects from upland to peatland sites were laid out so as to encounter a wide range of nutritional and hydrological conditions and volumetric soil samples were taken at 20 m intervals. For organic material, in particular peats, the correlation of ignition loss with CEC and total N were clearly higher when the variables were expressed volumetrically. The volumetric expression of variables made comparison of soils with varying organic matter contents possible. In preliminary analyses of the relationships between soil variables and dominant height of the tree stand on mineral soil sites volumetric exchangeable bases, pH and C/N -ratio in the raw humus layer showed a significant correlation.
The PDF includes a summary in Finnish.
The paper deals with the nutrient status of surface peat layer from virgin sedge-pine swamps and its relationship to peatland types. When the nutrients are expressed in mg/100 g peat, only easily extractable Ca and Mg correspond to the productivity status of the peatland type. N, P, and K levels in the herb rich sedge-pine swamp are generally lower than in the small sedge-pine swamps, which are the least productive ones. The differences between the site types in all the five nutrients become much clearer when the results are expressed in kg/ha. P, K, and Ca are significantly different between the site types, and correspond to the productivity of the site type. For N and Mg the same tendency can be seen. The organically bound nutrients N, and to a lesser extent, P appear to comply with the hypothesis of an increase in nutrient availability in Southern Finland.
The PDF includes a summary in Finnish.