Spatial and temporal variation in water availability across high mountain gravelly pavement herbfields affects the distribution of hydrophilic plant species

Gravelly pavement herbfields are a groundwater-dependant vegetation type; water composition and supply are hypothesised to be a crucial factor affecting the distribution of plant species in the community. We described the relationship between plant species distribution in pavements and the spatial and temporal availability and composition of water. Water flows into pavements varied through the growing season, as did lateral spread of water, and its permanency. Furthermore, the distribution of dominant pavement plant species was associated with moisture. Oreobolus pumilio (Cyperaceae) was significantly negatively associated, whilst Psychrophila introloba (Ranunculaceae) was significantly positively associated, with persistent moisture. The chemical composition of water changed whilst transiting through pavements, with loss of dissolved CO2 and an increase in pH likely due to strong CO2 evasion. When compared with other hydrologic units across the landscape, the chemical composition of pavement waters was between that of groundwater and peatlands, corresponding to their physical position in the landscape. These results have implications for the conservation of the gravelly pavement herbfield community. With climate change, reductions in water availability threatens the persistence of key hydrophilic species given their strong association with moisture. Reductions in areal extent, as well as re-organisation of the plant community, could be expected.