Mangrove Surface Elevation Loss after Tree fall during Extreme Weather

Abstract

Fringing mangrove forests are likely to experience increasingly severe weather events under climate change, including an increased frequency of tropical storms that may lead to mangrove mortality. Mangrove mortality can result in soil surface elevation loss through the death and compaction of roots, which can in turn alter the hydrology of the ecosystem and reduce its resilience to sea-level rise. In subtropical Queensland, Australia, an extreme weather event in early 2021 resulted in the death and toppling of large Avicennia marina trees on a creek edge in mainland Quandamooka (Moreton Bay). A set of three rod surface elevation tables were located meters away from the uprooted mangroves and were opportunistically measured for twenty months after the tree deaths. Surface elevation in the mangrove forest decreased by 26.3 ± 3.59 mm year− 1 following the severe weather event, when estimated using a traditional annualization approach for surface elevation loss data. Loss estimates using generalised additive models were able to account for non-linear change in surface elevation and were of the same direction as annualised estimates but an order of magnitude lower (-4.82 ± 0.03 mm year− 1). Surface elevation loss was the result of local root compaction, and subsequent recovery of elevation was the result of mangrove forest recovery through neighbouring tree root growth and canopy infilling. This study was the first to follow the change in soil surface elevation after the uprooting of A. marina at a single tree scale, providing insights for mangrove forest resilience under future sea-level rise.