© 1968 by Institute of Chartered Foresters
The Utilization of Solar Energy and the Formation of Storeys in Forest Stands
TIS
Lithuanian Scientific Research Institute of Forestry Girionys Kaunas, Lithuanian S.S.R., U.S.S.R. 
The effective utilization of solar energy in multi-storeyed forest stands is an important factor in their productivity. Up to the present, however, forest science has not paid due attention to questions of the light budget and the rational utilization of light by the storeys of stands.
For over 10 years the author has investigated the productivity of trees and the effectiveness with which they utilize solar energy on more than 200 permanent experimental areas of mixed and compound spruce/deciduous stands of the Lithuanian S.S.R., while various tending fellings were made.
As a result, a relationship has been established between the nutritional conditions, the physiological state, and the morphology of trees. On this basis, a classification of trees according to their development in mixed stands has been derived, and the transition of trees from class to class has been established.
Using this classification as a means of selecting trees for cutting, the principle underlying the formation of storeys in mixed stands has been established. According to this principle, the tending fellings should remove from each storey, provided it has a subordinate storey, the trees with a comparatively low index of profitable utilization of solar energy. The removal of these trees, leaving the trees with more efficient foliage, makes it possible to create an upper crown canopy in which the foliage is reduced by 10 to 12 per cent, but which is capable of forming the same quantity of wood at a given intensity of thinning.
The tending of stands in this way allows an increase of 7 to 8 per cent in the illumination of the lower storeys, which, in turn, produces an increase of 10 to 16 per cent in the aggregate current volume increment of timber on the best stems.