Habitats of halophytes.

Abstract Salt-tolerant plants occur all over the world in a number of different ecosystems, ranging from pristine alkaline semi-deserts and mangrove forests; through semi-natural meadows and pastures; to man-made habitats such as the environs of graduation towers; over irrigated arable lands with poor drainage in the tropics; and to city lawns in the boreo-temperate zone polluted with NaCl and CaCl2 during deicing. Natural habitats disappear because of urbanization, tourism and agriculture intensification. Since 1980 one-fifth of the Earth's mangrove biome has disappeared as well as more than one-half of alkaline steppes and nearly all Earth's coastal and inland salt meadows, glassworts and other annual communities of muds and sands, Mediterranean and warm Atlantic halophilous scrubs, vegetated sea cliffs and machairs. At the same time halophytes colonize new, man-made habitats, becoming dominant or even the sole species there. Some salt-resistant species, such as Rhizophora mangle in Hawaii and Spartina anglica in the UK, become dangerous invasive species. Mangrove swamps deserve more efficient conservation and restoration efforts since they shelter coasts from erosion, tsunami and storm surge; trap a wide variety of heavy metals; and provide habitats for juvenile fish, oysters and crustaceans. In the temperate and boreal zones the traditional land use of saline meadows and pastures needs to be maintained to preserve the original biodiversity and ecosystem services. Further halophyte domestication will lead to establishment of completely new, artificial agro-ecosystems to yield food, fodder and fuel, as well as fibre and phytoremediation, for rapidly expanding human populations. A range of halophyte crop cultivation systems can help to reduce damage caused by salinization of soils and freshwater, increase food production up to 70% by 2050 and combat coastal erosion in the era of climate change and global pollinator crisis. At the same time we need to eradicate some monospecific thickets built by invasive, alien halophytes to restore primeval, species-rich communities in areas of naturally high salinity.