Thinnings in forest management

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ANNUAL REPORT 2005

Core Values, Vision,     
Mission   
Strategic objectives   
Metla   
Reviews   
Forest-based      
entrepreneurship and      
forest environment      
models and databanks   
Forest ecosystems and     
social significance     
of forests   
Doctoral theses   
Events and seminars   
New projects   
Publications   
Resources   
New appointments   
Organization   

Photo: Erkki Oksanen

The results from thinning experiments initiated at Metla since the 1960s were compiled in a recently completed research project Thinnings in forest management.

The best time to do precommercial thinning is rather late, when the stand height is 5-8 metres. In fertile stands of Scots pine, where differences in stem quality are apparent, the first commercial thinning can be done earlier than normal. The purpose of this “quality thinning” is also to remove the most dominating trees with thick branches.

It is particularly important for Scots pine that a sufficient number of trees is growing in the stand, because pine is more sensitive to increment loss through thinnings than other tree species. Since spruce reacts quickly to thinnings and has better tolerance for high stand density than other tree species, rather wide limits can be set for spruce stands especially on fertile soil, both regarding the intensity and timing of the thinning. For silver birch the first commercial thinning must be done sufficiently early, because its crown length tends to shrink. However, silver birch is quick to increase its growth after thinning, so even the first commercial thinning can be intensive. Thinnings for downy birch should be made later and less intensively than for silver birch.

The profitability of the later commercial thinnings can be increased by removing larger log-sized trees and by leaving somewhat smaller, healthy and vital trees that will have time to reach the more valuable log-size later. This procedure, called "thinning from above", is suitable for Scots pine and Norway spruce but in birch stands it leads to increment losses.

The most important results of the studies are included in Tuottava metsänkasvatus (Profitable silviculture, in Finnish only) published by Metla and Metsäkustannus Ltd. The book comprises the final report of an extensive research programme Alternatives of silvicultural practices of forest management and their effects on forest production.

Additional information: www.metla.fi/hanke/3280/index-en.htm and www.metla.fi/ohjelma/mot/index-en.htm

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