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\hypersetup{pdftitle={Effect of \textit{Gmelina Arborea} Plantation Development on Soil Nutrients, Aboveground Biomass and Tree Nutrient Accumulation},pdfauthor={Jonathan C. Onyekwelu},pdfsubject={Tropentag 2016: Abstract},pdfkeywords={Aboveground biomass, Gmelina arborea, plantation development, productivity, soil nutrients, sustainability},pdfpagemode=None,colorlinks=true}
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\parbox[b]{13.4cm}{\centering \large{\textbf{Tropentag, September 18-21, 2016, Vienna, Austria}}\\[1ex] \Large{``Solidarity in a competing world ---\\fair use of resources''\\[2ex]}}
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\Large{\textbf{Effect of \textit{Gmelina Arborea} Plantation Development on Soil Nutrients, Aboveground Biomass and Tree Nutrient Accumulation\footnote{\textbf{Contact Address:} Jonathan C. Onyekwelu, The Federal University of Technology, Dept. of Forestry and Wood Technology, P.M.B. 704, Akure, Nigeria, \mbox{e-mail}: \email{onyekwelujc@yahoo.co.uk}}\\[0.8ex]}}
\normalsize{\textsc{Jonathan C. Onyekwelu}}
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\item[]{\small{\textit{The Federal University of Technology, Dept. of Forestry and Wood Technology, Nigeria}}}
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\index[author]{Onyekwelu, Jonathan C.}
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\textbf{Abstract}
\begin{abstract}
\normalsize{
The fast growth rate and high productivity of tropical forest plantation tree species and their high nutrient demand have raised site sustainability concern. The effects of plantation development on soil nutrients, aboveground biomass and nutrient contents were investigated in 10 to 28 years' \textit{Gmelina arborea} plantations in Oluwa and Omo forest reserves Nigeria. Growth data were obtained from 60 20m\,$\times$\,\mbox{20\,m} temporary sample plots (30 each from Oluwa and Omo). \textit{G.~arborea} biomass equations from Nigeria were used to estimate biomass. Soils samples were collected at 0---15, 15---30, 30---45 and 45---\mbox{60\,cm} depths from 6m\,$\times$\,\mbox{6\,m} sub"=plots within each sample plot. Soil and tree nutrients analyses were undertaken using standard procedures. Soil samples were also collected from adjacent undisturbed natural forests and compared with plantation soil nutrients. Depending on age, above"=ground biomass ranged from 81.5 to 392.1 t ha$^{-1}$. Biomass partitioning was 83.0, 13.5 and \mbox{3.5\,\%} to stem, branches and foliage, respectively. Tree size and age did not significantly affect tree nutrient concentrations. Nitrogen, Ca and Mg contents in tree tissue followed the order: foliage $>$ stem $>$ branches while K and P followed the order: foliage $>$ branches $>$ stem. About \mbox{80\,\%} of each nutrient was stored in stem and \mbox{20\,\%} in branches and foliage. Nutrient accumulation in plant tissues followed the order: Mg$>$N$>$Ca$>$P$>$K$>$Na. The overall effect of Gmelina plantation development on soil nutrients was not significant. Soil nutrients of old"=growth Gmelina plantation and natural forest were comparable. These suggests that Gmelina plantation development did not have adverse effect on soil nutrients. The \mbox{20\,\%} accumulation of aboveground nutrients in branches and foliage implies that there will be additional \mbox{20\,\%} nutrient input into the soil if branches and foliage are left on site after harvest. For long"=term site quality and sustainability of production, successive plantations should be managed on 25 years' rotation, lower rotation will likely lead to site nutrients depletion.}

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\noindent \textbf{Keywords:} Aboveground biomass, \textit{Gmelina arborea}, plantation development, productivity, soil nutrients, sustainability
\index[key]{Aboveground biomass}
\index[key]{Gmelina arborea@\textit{Gmelina arborea}}
\index[key]{Plantation development}
\index[key]{Productivity}
\index[key]{Soil!nutrients}
\index[key]{Sustainability}
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