Document ID: chunk:federal_register_of_legislation:F2023L01376:reg:3:p2
Version: federal_register_of_legislation:F2023L01376
Segment Type: reg
Provision Reference: reg 3 (pt 2/13)
Character Range: 89026–92148

have been shown to have higher reproduction relative to those within intact habitats due to higher availability of resources, especially light (Neal et al. 2010), however, it is thought that these benefits are outweighed by more pervasive threats of isolation and weed invasion (Pisanu et al. 2009). Moreover, Spain and Lowe (2011) found that levels of inbreeding in juveniles in M. tetraphylla populations was related to adult trees density which are higher within small fragments relative to those within intact forests. They speculate that higher levels of seedling establishment and survival in disturbed habitats may lead to higher levels of inbreeding in those habitats.
Land clearance is a Listed Key Threatening Process under the Environment Protection and Biodiversity Conservation Act 1999 (Cth).

Small population size
Genetic drift, loss of genetic diversity, inbreeding depression, factors affecting reproductive success, and ability to sustain critical population size all affect the viability of threatened species populations (Lindenmayer and Burgman 2005). When population size is reduced, genetic diversity can be reduced and population viability compromised, sometimes resulting in inbreeding as has been found in small, isolated populations of M. tetraphylla (Spain and Lowe 2011). Some species can tolerate high levels of inbreeding without loss of the ability to reproduce. Even so, small plant populations are still vulnerable to single disturbance events such as wildfire, drought, disease or heavy weed incursion.
The Macadamia species in this Plan occur primarily in small populations, however, considerable debate surrounds what constitutes a viable population in species with naturally small and spatially diffuse populations. In the case of Macadamias, habitat models predict that the species likely occupied contiguous areas of suitable habitat prior to arrival of Europeans and clearing. Limited dispersal ability and the patchy spatial pattern of rainforest communities in the landscape, however, especially in riparian systems, meant that populations were naturally small and patchily distributed in the landscape.
All Macadamia species can maintain themselves via coppicing, reducing the rate of loss of genetic diversity due to drift in small populations and partly explaining why Macadamias have retained relatively high levels of genetic diversity despite apparently naturally small population sizes. The effects of drift are likely to be slowly realised given the long generation times. Drift will lead to a loss of alleles and random differentiation between populations.
Macadamia populations could potentially maintain genetic diversity within fragmented small populations via gene flow due to pollen exchange if there is sufficient connectivity among populations within the landscape matrix. Interpopulation gene flow via pollen of 2.8 km has been documented for M. integrifolia (Neal 2007). Nearest neighbour distance calculations among recorded Macadamia populations show that for each species, many populations are located within 3 km of their two nearest neighbours, especially