Changes in the biomass and productivity of woodlands in the Sengwa wildlife research area, Zimbabwe.
Changes in biomass and annual production measured from 1972 to 1976 in four woodlands, the miombo, the Sengwa/Lutope riverine, the Manyoni riverine and the mopane woodland, are described. The greatest changes in biomass were recorded in the miombo woodland where it is estimated that the biomass decreased by 45%. The biomass of the Sengwa/Lutope riverine, a woodland with three strata, increased by 14%, whilst that of the Manyoni riverine changed little. The biomass of the mopane woodland decreased by over 6%. The annual production of the miombo, the Manyoni riverine and the mopane woodlands decreased between 1972 and 1976, whereas that of the Sengwa/Lutope riverine woodland increased. The change in the biomass of the miombo woodland was primarily a result of the removal by elephant of large trees which were not replaced due to the effects of elephant and fire. The increase in biomass of the Sengwa/Lutope riverine woodland was a result of recruitment to both the tree and shrub layers. The tree biomass increased by 394%, and the shrub biomass by 207% but the biomass of the upper canopy trees decreased by 10%. The decrease in biomass of the mopane woodland, which is seldom affected by fierce fires, was almost certainly due to the effects of elephant. Due to the opening up of the canopy and the coppicing of damaged trees, more browse is now in reach of the smaller browsing animals in all woodlands except the Manyoni riverine. Elephant appear to have been responsible for the decreases in biomass but fire has also contributed.