## 3 Results and Discussion
### Declining Syndromes in Ageing Plantations  
We monitored the health conditions of each _A. confusa_ tree within the four sites between August 2018 and October 2020 for 12 times to see the changes within two years. The total number of _A. confusa_ trees in the four slopes was originally at 262 to later 172, due to the phased selective removal of _Acacia_ trees and tree collapse under typhoons. At the end of the survey, 35.29% of existing _A. confusa_ were higher than 10 m, 30.59% were larger than 300 mm DBH, 30% were of 50% or more branch dieback, 60% were of poor health, and 88.24% possessed dead branches (Tables 4 and 5). The conditions of existing _A. confusa_ trees in these slopes were found to be very poor, with widespread symptoms and defects such as sparse foliage, dieback, trunk crack, poor tree form, and heavy leaning, etc. In addition, fungal infection by _Ganoderma tropicum_, _Pyrhardema adamantinum_, and _Amaurodema rugosum_ were observed on few trees with serious symptoms. The signs and symptoms indicated that most of the trees are declining and manifesting stress response. The health conditions were apparently deteriorating over the two years, which diminish the trees' ability to respond to structural issues. Ageing plantations of this kind, due to the high proximity to people and properties, should be properly maintained and managed. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**21 August 2018**} & \multicolumn{4}{c}{**23 October 2020**} \\ \hline \multirow{3}{*}{**Site**} & \multirow{3}{*}{**Slope No.**} & **No. of** & **Mean** & **Mean** & **Mean** & **No. of** & **Mean** & **Mean** \\  & & _Acacia_ & **Height** & **DBH** & **Dieback** & _Acacia_ & **Height** & **DBH** & **Dieback** \\  & & _confusa_ & **(m)** & **(mm)** & **(\%)** & _confusa_ & **(m)** & **(mm)** & **(\%)** \\ \hline \multirow{3}{*}{1} & 6 NW- & \multirow{3}{*}{63} & 9.32 & 290.2 & 23.12 & \multirow{3}{*}{37} & 9.76 & 331.86 & 29.59 \\  & D/C161 & & (0.25) & (10.89) & (2.23) & & (0.33) & (16.13) & (3.03) \\ \hline \multirow{3}{*}{2} & 6 NW- & \multirow{3}{*}{33} & 10.94 & 260.34 & 26.09 & \multirow{3}{*}{15} & 10.6 & 248.67 & 38.53 \\  & D/C158 & & (0.25) & (20.49) & (2.61) & & (0.46) & (23.62) & (7.28) \\ \hline \multirow{3}{*}{3} & 6 NW- & \multirow{3}{*}{99} & 8.43 & 227.01 & 40.73 & \multirow{3}{*}{57} & 8.69 & 227.89 & 43.33 \\  & D/C74 & & (0.19) & (9.71) & (2.21) & & (0.2) & (11.24) & (2.47) \\ \hline \multirow{3}{*}{4} & 6 NW- & \multirow{3}{*}{67} & 7.99 & 251.96 & 25.67 & \multirow{3}{*}{61} & 8.03 & 258.56 & 31.8 \\  & D/C78 & & (0.22) & (11.86) & (2.39) & & (0.23) & (12.63) & (2.67) \\ \hline \multirow{3}{*}{**Total**} & \multirow{3}{*}{**262**} & **8.83** & **252.17** & **30.82** & \multirow{3}{*}{**170**} & **8.86** & **263.36** & **35.78** \\  & & **(0.13)** & **(6.18)** & **(1.3)** & & **(0.15)** & **(7.69)** & **(1.61)** \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Mean height, DBH, and dieback percentage of _A. confusa_ in the study sites in Aug 2018 and Oct 2020. Values in parenthesis represent standard error of mean. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Species**} & \multirow{2}{*}{**Setups**} & **Annual GPP** & **Annual \(F_{\text{O3}}\)** & **Mean \(v_{d}\)** \\  & & **(g C m\({}^{-2}\))** & **(g O\({}_{3}\) m\({}^{-2}\))** & **(10\({}^{-3}\) m s\({}^{-1}\))** \\ \hline \multirow{3}{*}{_Acacia confusa_} & Measurement & 1595 & 3.125 & 3.52 \\  & ConV\({}_{\text{cmax\_MeaLAI}}\) & 1555 & 3.130 & 3.35 \\  & ConV\({}_{\text{cmax\_ConLAI}}\) & 2108 & 4.417 & 4.98 \\ \hline \multirow{3}{*}{_Liquidambar_} & Measurement & 2316 & 2.507 & 2.79 \\  & ConV\({}_{\text{cmax\_MeaLAI}}\) & 1531 & 2.201 & 2.47 \\  & ConV\({}_{\text{cmax\_ConLAI}}\) & 1554 & 2.225 & 2.50 \\ \hline \multirow{3}{*}{_Trema orientalis_} & Measurement & 2129 & 3.516 & 3.95 \\  & ConV\({}_{\text{cmax\_MeaLAI}}\) & 2216 & 3.637 & 4.08 \\ \cline{1-1}  & ConV\({}_{\text{cmax\_ConLAI}}\) & 2949 & 4.139 & 4.62 \\ \hline \hline \end{tabular}
\end{table}