Unlocking the potential of pioneer species Ecophysiological insights for mangrove restoration success in Mozambique

Increasingly vulnerable to climate change impacts, Mozambique has witnessed a surge in mangrove rehabilitation projects focused on protecting coastal areas. However, these initiatives predominantly prioritize climax species, overlooking pioneer species with rapid colonization abilities and high resilience to climate change. This study aims to address this disparity by providing information on the ecophysiology of pioneer species and their adaptability to high environmental constraints. To achieve this, we compared the habitats and productivity indicators of climax species (Rhizophora mucronata, Ceriops tagal, Bruguiera gymnorrhiza) with two pioneer species: Avicennia marina and Lumnitzera racemosa. A. marina thrives at both extremities of the intertidal gradient, while L. racemosa grows exclusively at the highest elevation in Saco Bay. In contrast to climax species, A. marina and L. racemosa form extensive stands landward in hypersaline habitats (up to 82 ‰) and poorly irrigated substrates with low organic matter (OM) content. We recorded water content values as low as 5% (27 ± 7% for climax-species stands), and bulk density ranging from 1.35 to 1.52 g cm-3. Pioneer species exhibited mean (± SD) stomatal conductance values (27 ± 16 mmol m² s-1) twice as low as climax species, enabling them to reduce leaf transpiration landward while adapting to waterlogged conditions seaward, especially for A. marina. Although lower stomatal conductance constrains photosynthesis and growth, pioneer species form stands of lower stature and biomass (8.51 to 26 Mg ha-1) compared to climax-species stands (83.74 to 250 Mg ha-1), but of higher resilience. Our results emphasize the capacity of pioneer species to thrive in harsh environmental conditions, particularly water stress caused by critical inundation rates, excessive insolation, and hypersalinity. Increasing the utilization of pioneer species is suggested to enhance the resilience of newly planted stands against climate change, particularly rising storms and drought, thereby more effectively safeguarding coastal areas.