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Population dynamics of an endangered heathland shrub, Epacris stuartii (Epacridaceae): Recruitment, establishment and survival
Author(s) -
Keith David A.
Publication year - 2002
Publication title -
austral ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.688
H-Index - 87
eISSN - 1442-9993
pISSN - 1442-9985
DOI - 10.1046/j.1442-9993.2002.01160.x
Subject(s) - seedling , shrub , biology , population , ecology , microsite , endangered species , quadrat , agronomy , habitat , demography , sociology
The only known population of the endangered shrub Epacris stuartii Stapf was studied from 1994 to 2001 using demographic census techniques. The effects of substrate, a fire and a storm on the emergence and survival of seedlings and the survival of established plants of different sizes were examined using failure‐time analyses and logit‐linear models. Ninety‐five per cent of seedling emergence was delayed until the second post‐fire spring, an unusual response among species with persistent soil seed banks. Mortality of seedlings was extreme compared with larger‐seeded species, but diminished significantly with age. Seedling mortality varied significantly between substrates: 40% of seedlings persisted for more than 5 years in mineral soil, whereas less than 10% lived more than a year on rock and intermediate substrates. However, seedling numbers and local densities were lower on soils than other substrates. Background mortality of established plants was lower on soil and intermediate substrates (0.5% per year) than on rock (3% per year). Small plants may be more susceptible than large plants on rock, but not on soil. Both the fire and the storm resulted in elevated mortality of established plants. The population exhibited a variable response to fire, with plants on rock and intermediate substrates behaving as obligate seeders, whereas plants in soil resprouted. This appears to be the first report of microhabitat variation in fire response at sympatric scales. The effects of the storm were apparently independent of substrate and plant size. The essentially independent disturbance regimes comprising recurring fires and storms are likely to have a profound effect on the long‐term population dynamics of E. stuartii . Over the 7‐year census period, recruitment has failed to compensate for mortality, resulting in a 30% net decline in the population. The demographic census has proved to be crucial in the detection and diagnosis of this decline.