to 2016. Renovation works were carried out on the area corresponding to 0.58% of the total forest area (from 0.32% in the Małopolskie voivodship to 0.91% in the Opolskie Voivodeship). According to GUS data, the area of forests in Poland from 1990 to 2017 increased by 548,000 ha. Increasing the area of forests occurs as a result of afforestation of non-forest land used for agriculture or for wasteland. The increase in forest area is also related to the reclassification of other lands covered with forest vegetation - since 2001, the area of afforestation resulting from natural succession has been shown in public statistics.
Figure 42. Forest renewals in 2017 by voivodships146
In Poland, currently about 1.5 million solid cubic metres of logs for energy (620,000 m³ coniferous wood and 818,000 m³ of deciduous wood) and 1.0 million cubic metres of small-size wood are obtained, i.e. together 2.5 million cubic metres147. According to estimates of the State Forests, the possibility of obtaining timber amounts to 2 Mm3 per year, and from 2020 it will be possible to obtain 4 million cubic metres. It is assumed that 1 solid cubic metre of wood is about 243 liters of heating oil and 1 kg of dry wood corresponds to the energy of 4.4 kWh. The wood consists of: cellulose, hemicellulose and lignin. Cellulose (C6H10O5) is the basic component of the plant substance and is about 40-60% in wood. In deciduous wood, cellulose is less than coniferous, namely: 43-47% leafy, 53-54% coniferous. Hemicellulose occurs in wood in an amount of about 15-20%, and the amount of lignin (C10H18O9) is 18-30%. Calorific values of individual components are indicative: hemicellulose 16.2 MJ / kg, lignin - 28.8 MJ / kg, cellulose - 17.3 MJ / kg and resins - 36 MJ / kg. The basic elements that are part of the wood are; coal (49.5%), oxygen (43.8%), hydrogen (6.0%), nitrogen (0.2%). The differences in the composition between different tree species are insignificant.
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Bureau for Forest Management and Geodesy, Central Statistical Office, state on 1 January 2017 Waldau A.J., Monforti-Ferrario F., Banja M., Arantegui R. L., Renewable Energy Snapshots 2013, Report EUR 26006 EN, EU 2013
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