Sub-boreal Forest ecosystems

The Boreal and Sub-Boreal Forest ecosystems represent the forests of cold and temperate climate. These ecosystems occupy an extended zone in the northern part of the Northern Hemisphere. The total area is 16.8 x 106 km2, or 11.2% from the whole World s territory. 

The plant species biomass of Boreal and Sub-Boreal Forest ecosystems accumulates a significant part of living matter of the whole planet. This value is about 700 x 106 tons of dry weight. The biomass per unit area of different Forest ecosystems varies from 100 to 300 ton/ha and even 400 ton/ha in the Eastern European Oak Forest ecosystems. The annual net primary productivity, NPP, varies from 4.5 to 9.0 ton/ha (Table 1). 

Since nitrogen is a nutrient, which limits the productivity of almost all Boreal and Sub-Boreal Forest ecosystems, its biogeochemical cycling is relatively well understood at present. The major N transformations and fluxes are shown in Figure 3. 

Denitrification, a dissimilatory pathway of nitrate reduction (see Section 3.3 also) into nitrogen oxides, N2O, and dinitrogen, N2, is performed by a wide variety of microorganisms in the forest ecosystems. Measurable rates of N20 production have been observed in many forest soils. The values from 2.1 to 4.0 kg/ha/yr are typical for forest soils in various places of Boreal and Sub-Boreal Forest ecosystems. All in situ studies (field monitoring) of denitrification in forest soils have shown large spatial and temporal variability in response to varying soils characteristics such as acidity, temperature, moisture, oxygen, ambient nitrate and available carbon. 

However, the microbial activity is depressed during long and severe wintertime, and this leads to an accumulation of semi-mineralizable plant residues on the soil surface. With the increasing duration of cold season from south to north, the mass of these half-destroyed remains enlarges from 15 ton/ha of dry organic matter in Broad-Leaved Sub-Boreal Forest ecosystems to 80-85 ton/ha in Northern Taiga Forest ecosystems. 

The data of Table 3 provide a general characteristic of trace element fluxes in Boreal and Sub-Boreal Forest ecosystems. 

The Broad-Leaved Forest ecosystems are widespread in regions of Sub-Boreal climate zone with a well balanced precipitationrevapotranspiration ratio. The southern periphery of the vast belt of Eurasian boreal and Sub-Boreal Forest ecosystems is represented by Oak Forest ecosystems. These ecosystems exhibit both the largest biomass and annual NPP rates in comparison with other forest ecosystems of this zone. However, the dead mass surface organic matter is 2-3 time less than that of coniferous forests. 

Biogeochemical processes in the soil-water system of Boreal and sub-Boreal Forest ecosystems... 

These ecosystems fall entirely within the continent. It is a crescent opening to the south, with the northern fringe at 50-58° N the southern tip of the long western arm of the crescent is at 38° N. The other boundary of the Forest-Meadow Steppe ecosystems coincides with the boundaries of the Boreal Taiga and Sub-Boreal Forest ecosystems. The inner edge of the crescent borders the closed Steppe ecosystems of the continent. 

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