Abstract: In this study, effects of altered rotation length, nitrogen deposition and changing climate on harvest removal and carbon sequestration of forest, as well as on economic profitability of forestry, were assessed. This study was based on simulations with a gap-type forest succession model in the conditions that represent Scots pine [Pinus sylvestris] stands in southern Finland. Both warmer climatic conditions and increased nitrogen deposition enhanced forest productivity and timber yield. This also shortened the optimum rotations based on mean annual yield and soil expectation value. The highest carbon stock in forests, i.e. the highest mean annual carbon stock in the forest over a rotation period, was achieved with long rotations and higher nitrogen deposition. However, a warmer climate had an opposite effect on the forest carbon stock, because enhanced decomposition of soil organic matter resulted in a lower carbon stock in the forest soil.
Abstract: xD;The response of understorey vegetation to addition of nitrogen and sulphur was examined in a 60-year-old Norway spruce (Picea abies Karst.) stand in southern Finland. The understorey vegetation was studied on experimental plots receiving nitrogen (25 kg N xD;ha-1) and sulphur (30 kg S ha-1) as ammonium sulphate once a year for 4 years. xD; xD;The dominant moss species on the site were Pleurozium schreberi (Mitt.) and Dicranum polysetum (Sw.). The biomass of the dominant moss species was decreased significantly by sulphur and nitrogen deposition during the study period. Due to the addition of nitrogen and sulphur, the biomass of Pleurozium schreberi was decreased by 60% and the biomass of Dicranum polysetum by 78%. xD; xD;Over a 4-year study period the responses of vascular plants to addition of nitrogen and sulphur were not significant. Forest-floor mosses seemed to be more sensitive to nitrogen and sulphur deposition than vascular plants were. Since bryophytes lack a cuticle and absorb water very rapidly after rain, they are exposed more to the direct effects of acid deposition than other plants are. Thus, mosses may indicate changes in forest vegetation due to acid deposition.
Abstract: Forest ecosystems may accumulate large amounts of nitrogen in the biomass and in the soil organic matter. However, there is increasing concern that deposition of inorganic nitrogen compounds from the atmosphere will lead to nitrogen saturation; excess nitrogen input does not increase production. The aim of this study was to determine the long-term changes caused by nitrogen input on accumulation of nitrogen in forest soils and in ground vegetation.
The fertilization experiments used in this study were established during 1958–1962. They were situated on 36- to 63-year old Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karsten) stands of different levels of fertility. The experiments received nitrogen fertilization 5–7 times over a 30-year period, and the total input of nitrogen was 596–926 kg/ha.
Nitrogen input increased the amount of organic matter in the humus layer and the nitrogen concentration in the organic matter. Furthermore, the total amounts of nutrients (N, P, K, Ca and Mg) bound by the humus layer increased due to the increase in the amount of organic matter. However, nitrogen input decreased the biomass of ground vegetation. The nitrogen concentration of the plant material on the nitrogen-fertilized plots was higher than that on the control plots, but the amount of nutrients bound by ground vegetation decreased owing to the drastic decrease in the biomass of mosses. Ground vegetation does not have the potential to accumulate nitrogen, because vegetation is dominated by slow-growing mosses and dwarf shrubs, which do not benefit from nitrogen input.
