# Evaluating Litter Yield and Decomposition for Re-Vegetated Mangroves in a Subtropical Mudflat
## 4 Discussion  
The field monitoring results suggest that the litter yield was subject to seasonal control (Figure 2). Autumn was the major period of litterfall following the strong growth period starting from late spring. Due to the low temperatures in winter, biomass production was low, leading to the low recorded litter yield. The litter yield increased after spring arrived as a result of enhanced biomass production for _Heritiera littoralis_ and _Kandelia obovata_. The lack of other litterfall peaks for _Thepesia populnea_ indicated that this species had a longer leaf life span, as compared to the other species. It has been established that different plants have different leaf senescence and fall dynamics [26; 27]. Amongst the three investigated mangrove species, the annual litter yield was in the following decreasing order: _Heritiera littoralis_\(>\)_Thepesia populnea_\(>\)_Kandelia obovata_ (Figure 3). Mangrove litter yield is directly related to geographical environment, species, and tree maturity [28]. The _Heritiera littoralis_ had a larger average diameter at breast height (DBH), average tree height, and tree canopy cover, as compared to the other two species. This might be partly responsible for its highest annual litter yield. The highest annual litter yield (745 g m\({}^{-2}\)) of the _Heritiera littoralis_ is comparable to the annual litter yield for the same species at other locations along the South China coast (Table 4). It is interesting to note that the investigated _Heritiera littoralis_ was much younger than that at the Jiulong Estuary and in Shenzhen. This suggests that tree age may play a weak role in affecting the litter yield when the mangrove tree reaches an age of nearly 10 years old. Figure 3: A comparison of litter yield among the three mangrove species. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Time (d)** & _Kandelia obovata_ & _Heritiera littoralis_ & _Thepesia populnea_ \\ \hline Original & 11.65 \(\pm\) 2.42a & 12.52 \(\pm\) 4.1a & 11.34 \(\pm\) 1.43b \\
90 & 11.32 \(\pm\) 2.13a & 11.34 \(\pm\) 0.31a & 10.39 \(\pm\) 1.42b \\
180 & 13.99 \(\pm\) 1.21b & 13.40 \(\pm\) 2.18 ab & 13.42 \(\pm\) 0.51a \\
270 & 13.82 \(\pm\) 3.01b & 12.28 \(\pm\) 1.34 ab & 11.56 \(\pm\) 0.52b \\
360 & 16.29 \(\pm\) 0.29b & 14.89 \(\pm\) 1.68b & 14.56 \(\pm\) 0.7a \\ \hline \hline \end{tabular} Different letters in the same column indicate a significant difference at \(p\)\(<\) 0.05.  
\end{table} 
Table 3: Organic carbon concentration (g/kg) in the surface soil layer (0–5 cm) underneath the added litter for the three selected mangrove plant species. The marked weight loss of the added mangrove litter within the initial 30 days was likely to be the result of rapid decomposition of the easily degradable component of the litter materials. The observed phenomenon of a higher WLR for shorter periods of incubation, relative to that for longer periods of incubation for some occasions, suggests that the environmental conditions for the 12 spots where the mangrove litter was placed on the soil for observing the effects of time on the litter decomposition were not consistent. This makes it inappropriate to use the data to illustrate the progressive decomposition of the mangrove litter during the monitoring period. However, as shown in Figure 4, there was a good linear relationship between the length of field incubation time and the litter decomposition rate for both the branch and the leaf portion of the three investigated mangrove species. Overall, approximately 50% or more of the added mangrove litter could be decomposed within one year for either the branch portion or the leaf portion of the three investigated mangrove species. This transforms to a litter decomposition rate of over 0.013 g per day. The decomposed litter could be incorporated into the underlying soils and consequently affect the soil carbon dynamics. It is interesting to note that within the initial 30 days of the field incubation experiment, the soil carbon