Summary

primary production and nitrogen uptake (Huhta et al., 1998). In the areas where lime
has been applied, nitrogen mineralization happens even 50 times faster than in the
areas where lime has not been applied. These processes are more active after
introduction of the earthworm species Aporrectodea caliginosa (Robinson et al.,
1992b). Earthworms have positive impact on microorganisms of the forest soils.
They favor mycorriza formation and facilitate plant growth (Haimi, Einbork, 1992).
By increase of earthworm density and introduction of new species due to lime
application, increases also earthworm impact on the soil processes. Earthworms are
an essential factor in humus formation processes. Consequently changes the podsol,
and mull humus begins to form (Lee, 1985; Deleporte, Tillier, 1999). Dendrobaena
octaedra brakes down borders between the organic layers of the soil, mixing the
upper horizons of organic matter. Aporrectodea sp., Lumbricus rubellus, L.terrestris
intensively mixes the upper ground cover layers with mineral layers in depth of 25 to
30 cm, what to a certain extent may be compared to a tillage. In the boreal forest
areas of the USA, introducing in the forest soils different earthworm species at the
same time, in the organic horizon of the soil was observed soil raw humus (mor)
transformation into a mull structure with a well formed Ah horizon rich in organic
matter (Frelich et al., 2006).
3.3. Latvia’s boreal pine forest eutrophication and transformation
During the last decades intensive changes have been observed in Latvia’s pine
forest vegetation due to atmospheric deposition, climate changes, and land utilization
changes. Pine forest plant societies become less stable, numerous uncharacteristic
foreign species aggressively spread among them. Due to intensive spread of
gramineae species in the forests, enhances formation of sod. Organic matters
agglomerate in the upper layer of the soil, thus obstructing regeneration of conifer
trees (Laiviņš, Laiviņa, 1991; Laiviņš, 1998). Great impact is also of transboundary
transfer of the pollution (including nitrogene compounds) and emission from the
local pollution sources. Intensive use of dolomite and limestone in construction and
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