The Lost Brisbane Macadamias need our help
Wild macadamias between the Brisbane and Logan Rivers are now extremely rare and will not survive without our help. Both the Brisbane and Redland City Councils are actively engaged in protecting these heritage trees – now the people of Brisbane and Redlands have an opportunity to collaborate with BCC, RCC and Wild Macadamia Conservation to rescue and protect the Lost Brisbane Macadamias.
The Brisbane River meanders through a rich diversity of habitats, but only a few areas, mostly where closed forest grows on volcanic-derived soils, are habitat for macadamias. The Brisbane and Logan River flood-plains created zones where macadamias did not grow, so that over millions of years macadamias growing between these two rivers evolved to be genetically distinct from their relatives to the north and south. The habitat for these Brisbane macadamias appears to have been around White’s Hill and Bulimba Creek tributaries, Mount Cotton and Tingalpa Creek.
As forest was cleared for the settlement of Brisbane, most of this macadamia habitat was lost.
Did macadamias grow wild around Brisbane?
Long before people lived in Australia, waterways we now know as the Brisbane and Logan Rivers meandered through a rich diversity of habitats. On a few areas, where closed forest grows on volcanic-derived soils, macadamias were part of complex sub-tropical forest ecosystems.
The Brisbane and Logan River floodplains created zones where macadamias did not grow, so that over millions of years macadamias growing between these two rivers evolved to be genetically distinct from their relatives to the north and south. Macadamia habitat north of the Brisbane River is mainly in the Pine Rivers catchment. South of the Brisbane River, macadamia habitat appears to have been around White’s Hill, tributaries of Bulimba and Tingalpa Creeks and Mount Cotton. As forest was cleared for the settlement of Brisbane, most of this macadamia habitat was lost – Mount Cotton is now the largest macadamia habitat surviving in the greater Brisbane area.
Using genetics to unravel the macadamia story
In 2020, Genetic short sequence repeat (SSR) markers were developed specifically for Macadamia and samples were taken of 160 presumed wild M. integrifolia from across the species’ geographic range. Population genetics and bioinformatic methods were applied to the SSR data from these samples and five main genetic clusters were identified, corresponding to geographic regions. One cluster included some historic planted trees including the Walter Hill tree (planted in the Brisbane Botanic Gardens in 1858) and a tree taken to California at around the same time. The only wild trees in this cluster grew at Mount Cotton and in Sankey’s Scrub at White’s Hill – all the others are planted, mostly in old orchards, some in gardens, presumably from nuts collected from the original habitat. These are the “Lost Brisbane Macadamias”.
Species Recovery Actions: Retain, Restore and Reconnect
In 2022 a further analysis of 293 trees was undertaken to identify M. integrifolia accessions that capture the genetics of the Lost Brisbane Macadamias. Of the trees tested (including some of the trees identified in the “Wild Macadamia Hunt” supported by the Brisbane City Council), 39 were found to assign over 50% to the Lost Brisbane Macadamias, 21 to over 80% and just 11 trees to over 90%. The original trees from Sankey’s Scrub at White’s Hill were the only wild trees with a high proportion of DNA from the Lost Brisbane macadamias.
Many of the trees tested from Mount Cotton are related to the Lost Brisbane Macadamias but also to macadamias from the north and south. This suggests that early plantings of orchards and backyard trees from other areas have cross-pollinated with the original trees at Mount Cotton over a few generations.
The mysterious Mount Bauple 