Changes of the norway spruce strictly protected forests in the Wigry National Park
The synthetic assessment of changes that happened in the Norway spruce mixed stands in the Wigry National Park (northeast Poland) in the years 1980–1999 was presented in the paper. The special attention was given to compare stands periodically or permanently excluded from any tending operations (strictly protected). The change of stand structure and intensity of tree dieback were assessed through the analysis of management plans from 1980 and 1996 and by the field inventory.
During 3-year period (1992–1995) 3% decrease of growing stock volume was recorded in the old spruce-pine forest in the Monkinie strict reserve. However that decrease was smaller than current annual volume growth of the stand. No significant differences were also found between annual volume of cuttings performed in the forests formerly (till 1995) excluded from tending activities (Monkinie, Studziany Las and Sarnetki reserves) and in forests managed on the regular way (2,8 and 2,9 m3/ha/year respectively). In the period 1980–1999 the growing volume of spruce in the analyzed stands (500 ha in total) decreased of about 35 m3/ha out of which 34 m3/ha during the last spruce bark beetle gradation. The highest decrease (about 200 m3/ha) were recorded in the Walik and Jezioro Długie reserves, with 60% spruce share reaching in stand of volume before the outbreak. Stands with 30–40% of spruce share were quite stable during the gradation.
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