Ephemeral wetland vegetation of Western Australia
Pignatti, Erika; Pignatti, Sandro
Vegetation with small short-lived species was first described from the SW corner of Western Australia (WA). This vegetation occurs on inselbergs and temporarily flooded areas in spring, after the rainy season. Several vegetation units have been described and on this basis in 1994 the Centrolepidi-Hydrocotyletea alatae vegetation class was proposed. Botanical investigations in desert areas of WA have been carried out during winter 2001 and 2002 in several localities of the Great Victoria, Gibson, Little and Great Sandy Desert. In all of them the presence of similar ephemeral vegetation in wet habitats has been observed. These communities also consist of short-lived species: germination occurs only after rare events of abundant, mostly erratic, rain and is followed in rapid life-cycles by flowering and dissemination; apparently the development of this vegetation is not concentrated in a particular season, because rainfall is unreliable and mostly linked to unpredictable La Niña events. Several communities can be recognized. They are rare and may occur around claypans, ephemeral ponds, natural and artificial pools. All of them are characterized by species of Centrolepidaceae, together with Cyperus, Marsilea, Triglochin, Stylidium, Scrophulariaceae tribus Gratioleae and insectivorous plants. A synoptic table gives the floristic composition of all the communities of the class Centrolepidi-Hydrocotyletea alatae, which is compared with ephemeral wetland associations of Italy as to vegetative adaptations and phytogeographical components. Data of intensity of PAR radiation, air and soil humidity and leaf temperature show that these vegetation types are adapted to very extreme microclimatic conditions, having the roots in the humid and relatively cool substrate, whereas leaves and flowers develop under dry atmospheric conditions, with elevated temperatures (over 30 °C in winter) at noon and frost during nights. Most of the species occurring in these communities are endemic.