Inundation and salinity regimes support blue carbon conditions in Australian temperate supratidal forests

In this study we report on new datasets of vegetation structure, carbon
cycling parameters, inundation and salinity patterns across 18 sites
spanning more than 4,000 km of Australia’s temperate coastlines. We report
site-specific ecosystem carbon stocks ranging from 169 to 635 Mg Corg
ha-1, with mean aboveground biomass (134 ± 63 Mg DW ha-1) and belowground
carbon stocks to 1 m soil depth (193 ± 98 Mg Corg ha-1), which are within
the range of national estimates for mangrove and saltmarsh ecosystems.
While there are variations in vegetation structure between sites dominated
by the genera Melaleuca and Casuarina, this does not lead to discernible
differences in above- or belowground carbon stocks. Organic matter
decomposition trends within supratidal forest substrates were similar to
adjacent mangrove and saltmarsh, though there were differences among study
sites and between labile versus recalcitrant tea litters. Soil-atmospheric
flux measurements conducted at one site were also within the range of
adjacent blue carbon ecosystems. We hypothesise that the high degree of
preservation of belowground carbon and low soil-atmosphere flux of
greenhouse gases is driven by a combination of infrequent surface
inundation, high water tables and typically saline groundwater in
supratidal forests, as measured across multiple settings. Supratidal
forests are carbon-rich ecosystems influenced by coastal processes
associated with tidal inundation. While further research is required to
understand the full distribution, carbon cycling and abiotic drivers of
supratidal forests, our findings strongly support their inclusion in blue
carbon and other management initiatives that support the response and
recovery of these endangered ecological communities in a time of change.