Cunningham & Milthorpe s.n., 2/8/73
NSW National Parks and Wildlife Service , July 2002
ISBN 0 7313 6517 8
6. Biology and Ecology
The NSW Herbarium records indicate that the herbarium specimens were plants collected in 1973 from individuals in the Coolabah population that were 10 to 15 feet high (3-5 m). Considering that these plants are still of a similar height, they were probably mature individuals 26 years ago, which suggests that the species is long lived given suitable conditions.
The primary mechanism for pollen dispersal in Bertya sp. Cobar-Coolabah is probably wind given that the flowers lack chemical and colour attractants and the styles and anthers are exposed. However, European honeybees have been observed visiting Bertya sp. Cobar-Coolabah flowers.
The capsules develop from the flowers in a small cluster located at the union of the leaf and stem. The capsules usually contain 1-3 seeds.
Flowering is generally believed to occur between July and August (Harden 1990), although timing is more dependent on the individual site characteristics. The Coolabah population has been observed flowering as early as June, whereas the Jacks Creek State Forest population usually flowers July to August. The two coastal populations, because of their different climatic and seasonal variations, normally flower in October-November, but can flower as late as February (J. Austen pers. obs.). However, plants in the Gibraltar Range population on the coast were observed to be in advanced bud in August 1991 and some plants had begun flowering (D. Binns pers. comm.).
In a study of flowering, Austen (1999) found that the number of seed capsules produced per branch and per individual varied greatly according to the site. In the Coolabah population, due to the advanced age of the plants, the only viable stem material suitable for flower production was on the last 150 mm of the branch. A typical individual, however, may contain 100 to 200 flowers in varying ratios of male to female flowers (average of 45 flowers/m2 of foliage, n=50 plants) (J. Austen pers. comm.).
The Jacks Creek State Forest population had the highest observed abundance of male and female flowers of any of the four main populations. The flowers per area of foliage were as high as 150 flowers/m2 on some individuals (J. Austen pers. comm.). These facts may reflect the apparent overall health of this population. Although this may also have been due to the above average rainfall recorded at this site in 1998.
The coastal populations had a much lower flowering ratio, which may have been due to the late flowering of the populations relative to the inland populations, or to the xeric nature of the outcrops on which the plant grew. The latter possibly influencing the amount of moisture available to the plants. Many individuals in the Kangaroo River State Forest population had no observed flowers or capsules on them, and the highest recorded amount of capsules on an individual was 240 capsules in an area of slightly less than 1 m2. A similar situation occurred in the small population at Gibraltar Range National Park, where many of the 20 individuals did not have any capsules on them at all (J. Austen pers. comm.).
The exact mechanism for seed dispersal is not known. Observations of capsule design suggest that the release of the seed is achieved through an explosive release, projecting the seed a short distance away from the parent plant. Movement by water may aid seed dispersal, where the substrate is hard enough to allow for surface run-off. Investigation of the seedbank in all sites showed that the majority of seeds were clustered around the base of the plant in a decreasing density that radiated outwards from under the canopy.
Seed viability and germination cues for Bertya sp. Cobar-Coolabah have not been investigated to date. Research on other threatened members of the Bertya genus indicates the seeds may contain a form of conditional dormancy (Scott 1997). This was determined after gibberellic acid (a germination hormone) was the only successful germination treatment in an experiment involving both heat and manual scarification.
Each population of Bertya sp. Cobar-Coolabah has a different age structure.
The Coolabah population is almost solely made up of mature and senescent individuals. Only two seedlings were observed in the entire population of 500-600 plants (J. Austen pers. comm.).
Jacks Creek State Forest has the largest and most robust population of Bertya sp. Cobar-Coolabah in New South Wales (>5 million plants). Almost the entire population consists of an even distribution of male and female plants and an even distribution of seedlings (J. Austen pers. comm.). Reproductive and germination success does not appear to be limited given the high densities of Bertya sp. Cobar-Coolabah in some areas. At one site, density was as high as 24 plants per 100 m2.
At Kangaroo River State Forest, the Bertya sp. Cobar-Coolabah population comprises approximately 500 plants with an equal number of juveniles as adult and senescent individuals. The number of seedlings is small, which is possibly due to a lack of disturbance in the past few years such that stimulation of the seedbank has not occurred.
The Gibraltar Range National Park population comprises approximately 20 plants and is similar to the Coolabah population in that it is senescent, comprising a single age class of over mature individuals. No seedlings, juveniles or young adult plants were observed in this population in 1999 (J. Austen pers. comm.). However, in 1991 young plants were observed, perhaps indicating the coastal populations are relatively short-lived (D. Binns pers. comm.).