Mangroves in arid regions: Ecology, threats, and opportunities

Mangroves are one of the few woody ecosystems that grow in hot-arid climates. They can survive extreme conditions of low precipitation, high solar radiation, wide temperature fluctuations and hypersalinity. These unique mangroves have distinct geomorphology, hydrology, forest structure, tree physiology, and soil biogeochemistry. In this review, supported by field data from Australia and Mexico, we explore the characteristics of mangroves in arid climates of the world. These mangroves are mostly tide-dominated with freshwater flows restricted to groundwater and sporadic tropical storms. They form dense forests with stunted growth dominated mainly by trees of the genus Avicennia that co-occur with salt marshes in the high intertidal. Their soils have low nutrient and carbon concentrations, and high soil δ15 N and δ13C values compared to subhumid and humid mangroves. Mangroves in arid climates have relatively low human pressure due to sparse human settlements. Key threats to these mangroves, which often persist at the edge of their physiological tolerances, include extreme drought, reductions in groundwater inputs, altered hydrology, sea-level fluctuations and increases in nutrient loading. Restoration of mangroves in arid climates should focus on restoring their hydrology. Mangroves in arid zones are under-represented in global maps and assessment programs, as they may not be consistent with countries’ definition of “forests”. Improved global representation and understanding of the ecology of mangroves in arid climates could help sustain their valuable ecosystem services.