In the Czech Republic, there are results of national forest inventories available from the years 1950, 1960, 1970, 1980, and 1990. Since 1979 the national inventory has been done annually. For the whole period, this time series indicates the rise in the average volume (in m3 ha1), the most rapid increase being at the 70th and 80th. The increase is affected by increasing average rotation period at the same time what results in harvest lower than the total increment. So the first 5 ten-year age stages have been of sub-normal area and the stand age structure has been shifting toward the overmaturity over 110 years. This also is a reason for the increase in the ratio of calamities in the total harvest. Although certain areas show the decrease in increment caused by immissions (more than 40 000 ha of dead forests were cut), this has not outweighed the general positive trends in the increment changes.
The author has elaborated the theoretical basis for modelling and designing scenarios of changes in forests development under the influence of calamities, and immissions, and increment changes based on the theory of random processes and namely he presented both the increment changes and increment as a function of a forest age and a calendar year; all based on the national inventories.
Other Czech authors have mentioned the positive changes in the increment stemming from thousands of repeated measurements of permanent sampling plots and have constructed original yield tables based on the increment scenario as a function of a stand age and a calendar year this year.
In Poland, attention has been focused on the decrease in the increment in the forests located in industrial regions and special occasional inventories aimed at damaged forests were done, too. The national inventories in Poland also show a gradual increase in average volume (m3 ha1).
These results are basically comparable with the results from the Czech forests and correspond with the geographical locations of both the countries.
Key words: growth trends, stochastic processes, increment as a function of ages and a calendar year, forest scenarios, yield tables.
Correspondence: Jan Kouba, Czech University of Agriculture in Prague, Faculty of Forestry, Kamycká ul., 165 21 Praha 6, Czech Republic
Fax: +42-2-325863