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Productivity of the assimilating apparatus is commonly defined as an increment in volume, most typically of the stem or trunk, per unit of crown size. In this paper the productivity of the assimilating organ (CPtwn1) is calculated as a quotient of the average annual increment in stem volume from a 5−year period (i v1) and the volume of twigs with needles (twnv), determined by xylometry methods (fluid displacement method). The experimental material comprised measure− ments taken on 200 Scots pines (Pinus sylvestris L.) in 8 pure pine stands growing in western Poland (tab. 1). Using the calculated sizes of assimilating apparatus, their arithmetic means and coefficients of variation were calculated for each stand (tab. 2, 3). Additionally, mean crown productivity within each Kraft's class comprising the dominant trees (classes 1, 2 and 3) as well as in the dominated trees (classes 4 and 5) were determined. The strength of the relationship between CPtwn1 and diameter at breast height (d1.3), height (h) and volume of leaved twigs (twnv) was calculated (tab. 4). Moreover, a two−way analysis of variance was conducted to assess the statistical significance of the effect of age of the stand and biosocial class of tree position in the stand (within the dominant trees and the dominated trees) on productivity of the assimilating apparatus. Mean productivity of analysed Scots pine crowns takes the highest values in the youngest stand (0.60 m3), while the lowest – in the oldest stand (0.34 m3). In the youngest, 25−year old pine stand, mean productivity of the assimilating apparatus in trees forming the dominated trees is by 124% greater than that of trees forming the dominant trees. An opposite situation is found in the oldest, 93−year−old stand, where mean productivity of the dominant trees is over 1.5 greater than that recorded in the dominated trees. Statistically significant effect of the stand age on productivity of the assimilating apparatus was observed (tab. 5). However, affiliation of a tree to the dominant or dominated trees does not result in such an effect. On the other hand, there is an interaction between age of the stand and its affiliation to the Kraft's classes. This means that the affiliation of trees to the dominant trees or the dominated trees and its effect on mean productivity of the assimilating apparatus depend on the age of stand.
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