Banksia Aemula - Ecology

Ecology

Most Proteaceae and all Banksia species, including B. scabrella, have proteoid roots, roots with dense clusters of short lateral rootlets that form a mat in the soil just below the leaf litter. These roots are particularly efficient at absorbing nutrients from nutrient-poor soils, such as the phosphorus-deficient native soils of Australia. A study of six wallum species, including B. aemula, found they have adapted to very low levels of phosphorus and are highly sensitive to increased levels of the element, leading to phosphorus toxicity. Some evidence suggests they are efficient at using potassium, and sensitive to calcium toxicity as well. A field study on North Stradbroke Island noted increased root growth in autumn (around April), but that overall root growth was more constant than other species looked at, possibly because its deeper roots had more regular access to groundwater.

A 1998 study in Bundjalung National Park in northern New South Wales found that B. aemula inflorescences are foraged by a variety of small mammals, including marsupials such as Yellow-footed Antechinus (Antechinus flavipes), and rodents such as Pale Field Rat (Rattus tunneyi), Australian Swamp Rat (R. lutreolus) and Grassland Melomys (Melomys burtoni) and even the House Mouse (Mus musculus). These animals carry pollen loads comparable to those of nectarivorous birds, making them effective pollinators. Grey-headed Flying Foxes (Pteropus poliocephalus) were also observed visiting B. aemula and their heads and bellies were noted to contact stigmas while feeding. Bird species that have been observed feeding at the flowers of B. aemula include Rainbow Lorikeet, Scarlet, and Lewin's Honeyeaters. Several other honeyeaters were recorded on B. aemula inflorescences for The Banksia Atlas, including the New Holland, Brown, White-cheeked, and Tawny-crowned Honeyeaters, Noisy Miner, Little Wattlebird and Noisy Friarbird. The Bundjalung field study found the Brown Honeyeater carried much higher loads of B. aemula pollen than other species measured, which included White-cheeked and Yellow-faced Honeyeaters and Silvereyes. Insects such as ants and bees (including the introduced honeybee) have also been recorded.

Banksia aemula resprouts from a lignotuber or shoots from epicormic buds after fire. Fire management of Banksia aemula heath in Southeast Queensland recommends 7- to 20-year fire intervals. Intervals of 10–15 years are recommended for the Eastern Suburbs Banksia Scrub, as longer leads to overgrowth by Leptospermum laevigatum. Experimenting with seed germination and early growth of B. aemula showed that phosphorus was toxic to seedlings, inhibiting growth at double normal soil concentrations and causing seedling death at quadruple normal soil concentrations. The addition of potassium or magnesium ameliorated these effects a little although potassium in high concentrations impacted on growth as well. Overall, seedlings grow slowly over the first 21 weeks of life compared with other plant species, the reasons for which are unclear, although it may be that it offers an increased chance of survival in a nutrient- or water-poor environment. Seed was killed by exposure to 150 °C, but survived seven minute exposure to 100 °C.

A study of coastal heaths on Pleistocene sand dunes around the Myall Lakes found B. aemula grew on ridges (dry heath) and B. oblongifolia on slopes (wet heath), and the two species did not overlap. Manipulation of seedlings in the same study area showed that B. aemula grows longer roots seeking water and that seedlings do grow in wet heath, but it is as yet unclear why the species does not grow in wet heath as well as dry heath. Unlike similar situations with banksia species in Western Australia, the two species did not appear to impact negatively on each other. A field study on seedling recruitment conducted at Broadwater National Park and Dirrawong Reserve on the New South Wales North Coast showed that generally Banksia aemula produced seedlings in low numbers but the attrition rate was low, and that seedlings had a greater survival rate on dry rather than wet heaths. Field work including the experimental planting out of seedlings at Crowdy Bay National Park showed that Banksia aemula seedling roots reach the water table within six months of germination, and that they can germinate in the presence or absence of recent bushfire. The reasons for bradyspory (that is fewer seeds with greater percentage of survival) is unclear, but may be a defence against seed-eating animals. Similarly in field work on North Stradbroke Island, B. aemula was noted to shed its winged seeds over time between (as well as after) fire, and germinate and grow readily with little predation by herbivores.