Plantations of pinus and eucalyptus replacing degraded mountain miombo woodlands in Mozambique significantly increase carbon sequestration

Abstract

Total ecosystem carbon (C) stocks in tree biomass (aboveground and belowground), litter layer and soil (0–50 cm depth) were quantified in mountain miombo woodland and in 34-year-old first-rotation plantations of Pinus taeda and Eucalyptus grandis. The study was performed at three sites (Penhalonga, Rotanda and Inhamacari) in the western highlands of Manica province in Mozambique, bordering Zimbabwe. One 30 m × 30 m sampling plot was established for each forest type per site. Pre-tested allometric equations were used to determine total C stocks within aboveground tree biomass of each forest type and data from the literature on the relationship between aboveground and belowground biomass were used to estimate C stocks in belowground woody biomass (i.e. coarse roots). Measured soil and litter layer C data were taken from a previous study. Carbon stocks in mountain miombo woodland were used as a baseline to estimate C sequestration at the ecosystem scale, i.e. net ecosystem production (NEP) in the plantations, considering 34 years as stand age of the planted forests. Total ecosystem C stocks in miombo woodlands (∼116 Mg ha−1) were significantly lower than in stands of P. taeda (363 Mg ha−1) and E. grandis (∼407 Mg ha−1). Carbon sequestration rate at ecosystem scale (NEP) was 7.24 Mg ha−1 yr−1 in P. taeda stands and 8.54 Mg ha−1 yr−1 in E. grandis stands. NEP was dominated by the increment in biomass (∼80%). This was also reflected in higher ratio between biomass C and soil organic C stocks in the plantations compared with miombo forest. The plantation species showed similar performance with respect to total C stocks and NEP. It was concluded that plantations of P. taeda or E. grandis have significant potential to increase C stocks and C sequestration rate in both soil and tree biomass on replacing degraded mountain miombo woodlands in the western highlands of Manica province.