Habitat Ecology and Physiological Response of Sticta filix and Pseudocyphellaria delisei from Tasmania

Sticta filix and Pseudocyphellaria delisei, two of the most wide- spread Tasmanian lichens, reach greatest dominance in areas of precipitation of approximately 1600 mm yr-'. Both species occur on a variety of corticolous, terricolous and saxicolous substrates in areas with up to 3000 mm yr-1 precip- itation, but S. filix is absent where precipitation is less than 1200 mm yr-'. Although both species show a similar range of high thallus water holding capacity, P. delisei is more drought resistant due to its ability to photosyn- thesize at relatively low thallus water contents. Its low quotient of maximum CO2 fixation rate to dark respiration rate indicates a greater adaptation to cooler conditions. Sticta filix maintains a significantly higher rate of CO2 fix- ation on a chlorophyll basis, on a dry weight basis and on a unit area basis. Under saturated thallus moisture conditions the rate of photosynthesis in S. filix is reduced less from maximal levels than that of P. delisei. These factors, combined with the low light compensation point in S. filix, account for the relative dominance of S. filix in shady forest habitats and P. delisei in more open sites.