Above-ground woody biomass structure and productivity in a Zambezian woodland

Abstract

A survey of standing woody (leaf and wood) biomass was made in a Zambezian Brachystegia/Julbernardia (miombo) woodland in the Copperbelt area of Zambia during 1988. Woody biomass data obtained from destructive stem samples from Central and Copperbelt areas of Zambia were used to develop regression models for estimating dry weights of woody biomass components from stem-diameter data. These models were then applied to stem census data collected during 1982–1988 from 45 coppiced and old-growth plots to determine the structure of woody biomass in miombo woodland in the Copperbelt area. Mean wood biomass of 234.7 t ha −1 ( sd = 35.9 ) on small (0.02 ha) sample plots was significantly higher than that of 89.2 t ha −1 ( sd = 13.6 ) on large (> 0.10 ha) sample plots ( t = 7.68, P < 0.001) in old-growth woodland. The overall mean woody biomass of 92.5 t ha −1 ( sd = 14.1 ) on large old-growth woodland plots was made up of 3.6% leaf and 96.4% wood. Mean annual increment ( mai) in wood biomass in coppiced plots aged 3–29 years was estimated at 1.97 t ha −1 ( sd = 1.68 ), but this ranged from 0.41 t ha −1 ( sd = 0.34 ) on plots aged 3–6 years to 2.91 t ha −1 ( sd = 1.41 ) on plots aged 7–29 years. The mai in experimental plots aged 48–49 years was 1.68 t ha −1 ( sd = 0.39 ). Among coppiced plots aged 3–6 years the mai of 0.60 t ha −1 ( sd = 0.35 ) on early-burnt plots as 2.7 times that of 0.22 t ha −1 on the late-burnt plots. Leaf biomass was not significantly different between coppiced plots aged 7–29 years and old-growth miombo woodland plots. The overall mean leaf biomass was 3.62 t ha −1 ( sd = 1.90 ). Mean leaf biomass as a percentage of mai in wood biomass represented 128% in coppiced plots aged 7–29 years and 177% in experimental plots aged 48–49 years. However, in coppiced plots aged 3–6 years there was no significant difference between mai and leaf biomass.