%0 Articles
%T Restoration of degraded dry semideciduous forest ecosystems in Ghana: Effects of African mahogany species on soil chemistry, tree diversity and the application of leaf morphometrics for provisional seed zonation
%A Danquah, Jones Abrefa
%D 2012
%J Dissertationes Forestales
%V 2012
%N 148
%R doi:10.14214/df.148
%U http://dissertationesforestales.fi/article/1931
%X The dry semideciduous forest zone is one of the most fragile and highly threatened ecosystems in Ghana. Recurrent bushfires and other anthropogenic disturbances have degraded this forest zone and converted a large proportion to savannah woodland. Moreover, the invasion of weeds following disturbances has impeded natural regeneration. Hence, the likely solution to this problem is restoration through the use of native forest tree species to catalyse natural regeneration. The use of African mahogany species in this regard has been emphasised. This study aims to (i) investigate the levels of phenotypic plasticity and ecogeographic and morphometric variation as well as similarity among populations of Khaya anthotheca and Khaya ivorensis with respect to leaf morphology as a basis for developing a preliminary framework for seed zonation for restoration; (ii) determine the effects of stand structure and native tree density on the recruitment of mahogany species in line-enrichment planting; and (iii) assess the effects of mahogany species on resident or native tree species diversity and soil chemical properties in restorations of degraded semi-deciduous forest ecosystems in Ghana.

The results of the study indicated a highly significant phenotypically plastic response of leaf morphology to precipitation, temperature, altitude and latitude in Khaya ivorensis populations. In addition, it was established that leaf size in Khaya ivorensis and K. anthotheca varies inversely with latitude, annual potential evapotranspiration and aridity index. However, leaf traits vary directly with a precipitation gradient among the respective species. The results suggested a south-north clinal relationship to leaf traits, with the southern populations of the two Khaya species having larger leaf sizes than the northern populations. Thus, seeds collected from higher latitudes could be planted in the same zone or moved to lower latitude with high amounts of rainfall. However, the results from Poisson regression modelling indicated that stand basal area, growing space and crown diameter were positively associated with recruitment. However, stand dominant height was negatively associated with recruitment. The results indicated that mixed mahogany species foster the recolonisation of a diversity of native tree species and accelerate the regeneration rate in the restoration of fire-degraded dry semi-deciduous forest ecosystems compared to natural regeneration. Moreover, relatively higher amounts of Ca, Mg, base saturation, CEC, organic C and organic matter and low amounts of Al were recorded in the soils beneath mixed mahogany plantation sites compared to natural regeneration sites.