## 4 Discussion  
The very high spatial resolution map of the aboveground carbon content in saltmarsh derived from the airborne ArborCam image provided important insights into the fine-scale spatial distribution of aboveground carbon. The aboveground carbon content was found to be higher at the boundaries between saltmarsh and _Casaurina_ forest and between saltmarsh and mangroves. The importance of these saltmarsh boundaries has been highlighted in previous research into the impacts of climate on blue carbon ecosystems, with a particular focus on the changing boundaries between saltmarsh and the surrounding mangroves [10; 11; 50; 51]. Saltmarsh boundaries remain a key consideration in monitoring and predicting the potential impacts of climate change on blue carbon ecosystems, and our results support the importance of saltmarsh boundaries as particularly crucial areas of relatively high aboveground carbon storage. Species-specific relationships were found between the ArborCam NDVI and the aboveground carbon content of saltmarsh vegetation, with much stronger correlations when quadrats were partitioned into two species groups (herbs, grasses, and sedges; and rushes). This partitioning corresponds with the species groups adopted in other saltmarsh studies conducted in south-east Australia [24; 35]. Quadrats with the dominant rush species,  
Figure 9: (a) Local monthly rainfall from January 2020 to March 2021 and mean monthly rainfall from all available years (Bureau of Meteorology, 2021) overlaid with mean PlanetScope NDVI for all saltmarsh quadrats (\(n\) = 47). (b) Relationships between monthly rainfall (all months, and high rainfall outliers in July and August excluded) and PlanetScope NDVI for all saltmarsh quadrats (\(n\) = 47) from April 2020 to March 2021. J. kraussii, had far greater aboveground carbon content than the other species with similar NDVI values. This may be due to its greater height, yellow/brown coloration, or higher proportion of non-photosynthetic components. _J. kraussii_ has been identified by other saltmarsh studies as a dominant saltmarsh species with a high carbon content [35; 50; 52]. The estimated mean aboveground carbon content of the study area (1.32 Mg C ha\({}^{-1}\)) was derived using the model based on the ArborCam NDVI extracted for the herbs, grasses, and sedges quadrats only, and it is therefore likely to have been underestimated by excluding the _J. kraussii_ quadrats with a higher aboveground carbon content. More accurately estimating the aboveground carbon content contributed by _J. kraussii_ is important, and the presence of species-specific relationships between NDVI and aboveground carbon content indicates that one model cannot be generalized across all saltmarsh species. A species distribution map is therefore a prerequisite for more accurate maps of the spatial distribution of the aboveground carbon content in saltmarsh vegetation and for estimating the total aboveground carbon content across a saltmarsh ecosystem using the optical remote sensing techniques employed here. Possible areas of tidal inundation of saltmarsh vegetation could also have resulted in an underestimate of the spatial distribution and mean aboveground carbon content. Tidal inundation can significantly impact the reflectance of saltmarsh vegetation, resulting in a decrease in the NDVI [37]; however, the ArborCam image was captured at low tide to reduce the potential confounding effects of tidal inundation on our results. The relationships between aboveground carbon and all the potential normalized difference band combinations derived from the ArborCam image highlighted potential species- and wavelength-dependent improvements for estimating aboveground carbon. For herbs, grasses, and sedges, a combination of red or red-edge, and red-edge or NIR produced the strongest correlation, while for _J. kraussii_ it was the combination of green or red and red-edge or NIR.