## 3 Results
### Historical Scenario: Biomass Production over the Entire Nkayi District  
The overall Nkayi district average trends in biomass production over the baseline (historical) period of 30 years (1980 to 2010) in relation to rainfall totals are presented in Figure 7.  
\begin{table}
\begin{tabular}{l c c c} \hline \hline \multirow{2}{*}{**Core Questions**} & \multicolumn{3}{c}{**GCM Scenarios**} \\ \cline{2-4}  & \multicolumn{3}{c}{**Historic Scenario (1980–2010)**} \\ \hline  & 1. & No change in historical rainfall and temperature & 2. & With/without increased carbon dioxide (400 ppm to 650 ppm) \\ \cline{2-4}
1. What are the temporal and spatial dynamics of biomass production from the three layers? (tree, shrub, herbaceous) 2. How do the livestock populations respond to changes in the vegetation? & \multicolumn{3}{c}{Hot and wet scenario} \\ \cline{2-4}
5. & 7\% increase in rainfall and 4 & 4. & With/without increased carbon dioxide (400 ppm to 650 ppm) \\ \cline{2-4}
5. & 7\% decrease in rainfall and 4 & 6. & With/without increased carbon dioxide (400 ppm to 650 ppm) \\ \cline{2-4}
5. & 7\% decrease in rainfall and 4 & 6. & With/without increased carbon dioxide (400 ppm to 650 ppm) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Core questions that guide SAVANNA simulations with historic and GCM Scenarios.  
Figure 7: Trends in peak biomass production (g/m\({}^{2}\)) over a period of 30 years (Historic scenario without climate change effects).  
In these baseline simulations, the shrub layer increased significantly over 30 years from about 300 g/m\({}^{2}\) in the early 1980s to over 1200 g/m\({}^{2}\) in the year 2010. A three-fold increase was realized in the woody plant layer (shrubs and trees) where biomass increased from 1980 production levels of approximately 30 g/m\({}^{2}\) to being almost steady around approximately 100 g/m\({}^{2}\) by 2010. The herbaceous layer does not increase over the historical period with biomass fluctuates between 200 and 400 g/m\({}^{2}\) over the years, primarily in response to rainfall amounts. Rainfall levels of less than 600 mm/year have the largest negative effect on herbaceous biomass production. Specific drought years such as 1992 and 2002 have production levels close to 120 g/m\({}^{2}\). Conversely, rainfall totals over 1000 mm/year positively influenced biomass production levels to over 300 g/m\({}^{2}\). Both the shrub and woody layers have less direct connection to seasonal rainfall totals. A study carried out by [43] on modeling the semi-arid grazing systems showed a pattern similar to the findings of this study on the trends of biomass production. Using the average rainfall and the monthly averages of the biomass yields for the 30-year period a general pattern of the relationship between the rainfall and the biomass was established. The grass layer fluctuates around fluctuating rainfall while the tree and shrub layers are less sensitive to variations. The amount of biomass from the woody layer does not change much during the year. The herbaceous and the shrub layer follow the same pattern, but the shrubs are much higher than the herbaceous layer. The herbaceous layer peaks around February and March and is at its lowest during the August to October period. (Figure 8).