BIOMASS AND PRODUCTIVITY OF AN AGE SERIES OF THREE COTTONWOOD CLONES (<em>POPULUS</em> <em>DELTOIDES</em>) IN CENTRAL HIMALAYAN TARAI REGION, INDIA

Abstract

This paper deals with estimates of biomass and net primary productivity of three clones of Populus deltoides, namely, IC, D-121 and G-3. Each of the three clones had one young (four years old), one middle age (six years old) and one mature (eight to 10 years) stand. All stands had similar stocking (667 trees ha^-1) at the time of plantation, but mature stands developed into stands with the lowest stocking (400—505 trees ha^-1) due to stem mortality with progressing stand age. Highest basal area (22.8—24.1 m²ha^-1) was attained by mature stands. Parabolic volume did not vary markedly from that of wood volume for young and middle age stands but showed wide variation in mature stands. Total tree biomass in investigated clones increased from young (32—42 t ha^-1) to mature stands (120—170 t ha^-1), the lowest and highest biomass being in IC and G-3 clones respectively. Net primary productivity also revealed similar pattern. At maturity, net productivity was in the order: D-121 (23 t ha-1 year^-1) > G-3 (21 t ha^-1 year^-1) > IC (14 t ha^-1 year^-1). The ratio of stem to leaf production generally decreased with age from around 2.0 in young stands (D-121 and G-3 clones) to less than 1.0 in mature stands. The relationship between biomass and net primary production was very weak. However, if biomass estimates for IC clone were excluded, a significant positive correlation (r = 0.956, p < 0.01) was achieved. Weighted mean height and aboveground net production were also significantly related (r = 0.973, p < 0.01).