Document ID: chunk:federal_register_of_legislation:F2023L01376:reg:3:p1
Version: federal_register_of_legislation:F2023L01376
Segment Type: reg
Provision Reference: reg 3 (pt 1/13)
Character Range: 86233–89285

3               Threats

Biology and ecology relevant to threats

Habitat loss and fragmentation
The long-term impacts of land clearing and habitat fragmentation are underlying factors contributing to the threatened status of Macadamia species. This is exacerbated by ongoing clearing of remnant bushland throughout south east Queensland and north east NSW for horticulture, agriculture, urban and industrial development and associated infrastructure.
The extent of land clearing in some areas of Macadamia habitat has dire consequences for long term persistence of Macadamia species in those areas. Approximately 80% of the Regional Ecosystem communities, most frequently occupied by M. integrifolia and M. ternifolia in Queensland within core areas of their respective ranges, have been cleared (Powell et al. 2014). Depending on the Macadamia species, between 30% and 50% of recorded populations in Queensland occur in areas that are either cleared or are patches of remnant vegetation too small in area to be included in 1:50,000 (SEQ) or 1:100,000 (non-SEQ) regional ecosystem mapping undertaken by the Queensland Herbarium. In NSW, almost the entire extent of the former Big Scrub, thought to comprise the core range for M. tetraphylla, was cleared in the 19th and early 20th centuries (Floyd 1990). Most extant populations of M. tetraphylla occur along the fringes of this area and the foot slopes of Wollumbin (Mount Warning) and its caldera.
Whilst a number of populations of Macadamia occur in protected tenures, such as National Parks and Conservation Reserves, many populations are located on private land. The loss of individual trees or small populations from private land particularly is difficult to detect, reducing the effectiveness of the legislative protection afforded to Macadamia species by State and Commonwealth governments. A relatively large number of Macadamias occur as a single or few individuals in paddocks (left for their edible nuts when the land was cleared), in roadside remnants, or in gullies and scarps too steep to be cleared. These scattered individuals and small populations may have an important role in maintaining connectivity among the population network for each species; ensuring the long-term persistence of these populations, however, is problematic.
Documented impacts of habitat fragmentation on Macadamia species include weed invasion, reduced frequency of optimal outbreeding distance among populations, genetic isolation of populations, and genetic population differentiation resulting in increased population divergence and likely eventual loss of genetic variation in future generations (Pisanu et al. 2009; Spain and Lowe 2011). Fragmented habitat areas are also likely to be more susceptible to fire. Populations in smaller fragments 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