The study of the growth of old-drained spruce forests (drained more than 40 years ago) has shown that already in the first five years after drainage diameter and height increment is 24 fold. As a consequence of diameter and height growth a stock increment is observed. A current mean periodic increment during 50 years after draining spruce forests is quite high and makes up 5.16.3 cubic metres/ha annually.
The efficiency of reclamation is determined by extra stock increment. Comparing the yield of drained and undrained spruce stands has shown that as a result of draining under Karelian conditions a considerable extra increment can be obtained between 1.4 and 4.7 cub.m/ha annually. In connection with a significant growth during the first 20 years a marked decrease in the density of newly formed wood takes place. In plots it decreased by 13.718.9%. The indices of wood density at compression along wood fibres correspondingly reduced by 21.823.3%. Later (in 20 years after drainage) the density somewhat increased, a result of an age factor on the one hand, and a decrease in growth rate, on the other. Because of different values of swelling and drying coefficients on the boundary between the wood formed before and after reclamation, checks may appear at wood kiln drying.
The study of timber defects in drained spruce forests has shown that the number of trees affected by rot reaches 23% of the total number of stems in spruce stands. The harvest of timber in drained spruce stands compared with spruce stands growing on mineral soils is lower by 38%. The research has shown a high efficiency of drainage in spruce forests. A fall in spruce timber quality should be taken into account at general assessment of forest drainage being the most effective means for increasing forest productivity.
Key words: spruce forests, drainage, increment.
Correspondence: Vladimir Ananyev, Forest Research Institute, Karelian Research Centre, 11 Pushkinskaya str., 185610 Petrozavodsk, Russia