Topography alters stand structure, carbon stocks and understorey species composition of Cedrela odorata plantation, in a semi-deciduous forest zone, Ghana

Abstract

Pure plantations established across different topographic positions may respond differently and exhibit varied stand characteristics. However, there is limited information on variability of pure plantation stand attributes along topographic gradients, particularly in West Africa. This study examined the stand structure, carbon stocks and understorey woody species composition of relatively older Cedrela plantations on three topographic positions within the deciduous forest zone of Ghana. About 15, 40 × 40 m plots were surveyed in 23-year-old Cedrela odorata plantations located on hill top, flat terrain and valley bottoms in the Tinte Bepo Forest Reserve, Ghana. Data were analysed using ANCOVA, Bayesian modelling of diameter distribution and correspondence analysis.Diameter at breast height (DBH; p<0.0001), total height (p<0.025), and stem density (p<0.001) were significantly different among the three topographic areas. Trees on the valley bottom had the highest DBH, total height, and biomass carbon while the highest stem density and basal area occurred on the flat terrain. Slope explained 63% of the total variability in the stem density of the C. odorata stand. Bayesian modelling of diameter distribution revealed that the 3-parameter Weibull function better fitted the diameter distribution of the trees on the hill top while the Johnson SB was more appropriate at the flat terrain and the valley bottom. Understorey woody species composition was significantly different among geomorphic positions. Differences in aboveground biomass carbon stocks among topographic positions were not significant.The local topography therefore severely alters plantation stand structure, leading to different distribution models being adopted at different topographic positions. Furthermore, cedrela plantations facilitate climate mitigation, species recruitment and functional/trait diversity differences along topographic gradients. This has implications for large scale plantation development especially on heterogeneous terrains.