PHYTOMASSES AND PRIMARY PRODUCTIVITIES OF DIFFERENT AGED POPLAR (POPULUS CV ROBUSTA) PLANTATIONS (HAINAUT, BELGIUM)

Phytomasses and primary productivities of different aged poplar (Popul us cv. robusta) plantations (Hainaut, Belgium). - In this paper are pr esented the living vegetal biomasses (phytomasses) and primary product ivities of different aged (31,24 and 8 years) poplar's plantations in the limoneous countryside of Hainaut (central Belgium). The mean heigh ts of the plantations are respectively 28, 25 and 8.5 m. Shrubs and he rbaceous layers are quite nitrophilous. The 31 years old poplar's plan tation has a total phytomass (dry mass) of 177 t/ha (159 t aboveground and 18 t below ground) and a primary productivity of 30.5 t/ha/year ( 28 t and 2.5 t); the 24 years old plantation has respectively 76.5 t/h a (68.5 t and 8 t) and 18 t/ha/year (16.5 t and 1.5 t); and that of 8 years, 11 t/ha (9 t and 2 t and 8 t/ha/year (7.5 t and 0.5 t). Phytoma sses and primary productivities for the poplar alone are respectively about 96% and 86% of the total in the plantation of 31 years old, 86% and 66% in that of 24 years; and only 31% and 22% in that of 8 years. True increment reaches 24 t/ha/year for the 31 years old plantation, 1 3 t/ha/year for the 24 years and 2 t/ha/year for the 8 years. Photosyn thetic efficacity of the oldest plantation (31 years) is 1.8%.