Reef, R. and Gordon, C., 0000. Allometric equations for aboveground biomass estimation of temperate mangroves using uncrewed aerial vehicles.
Temperate mangrove ecosystems face different stresses compared with their tropical counterparts, resulting in reduced extent, biodiversity, and productivity. Temperate mangroves represent less than 2% of global mangrove cover and are thus less studied, but where they occur, they provide distinct ecosystem services and are expanding. Avicennia marina subsp. australasica is the sole mangrove species found in Victoria, Australia, where mangroves reach their highest latitudinal limit globally. Estimating aboveground biomass (AGB) in temperate mangroves poses challenges because of their morphological differences from tropical forests. This study used uncrewed aerial vehicle (UAV)–derived measurements and ground inventory data to develop allometric equations for A. marina at its latitudinal limit. A hybrid allometric equation, incorporating both field- and UAV-derived metrics, provided the most accurate prediction of AGB (coefficient of determination [R2] = 0.93). An allometric equation using solely UAV-derived inputs (canopy area and canopy height) had high-fidelity prediction capacity (R2 = 0.85), although it overestimated AGB by 11%. A significant finding was the simplification of scaling from individual tree AGB to landscape-scale AGB by eliminating the need to segment individual tree canopies. Landscape-scale AGB estimates showed a stable underestimation of approximately 30%, which could be improved by segmenting the area into zones of similar height. AGB of mangroves in Western Port was estimated at 48 t ha−1, which is within the range measured for temperate mangroves around the world. The biomass density in this temperate region is significantly lower (40%) than the continental average.