Threat assessment

Threats to the Wet Tropics of Queensland are detailed in the IUCN World Heritage Outlook Assessment reports from 2014, 2017, and 2020. These reports, previously published every three years, will now be published every five years. The next one is due out in 2025. The Wet Tropics Management Authority also releases an annual State of the Wet Tropics Report, which tracks threats and major issues affecting the region.

Climate change

Climate change poses significant threats to the Wet Tropics, impacting its unique flora and fauna. Over 15 years ago, predictions suggested that more than 50% of endemic vertebrate species could face extinction due to climate change. Recent studies have recorded declines that align with these predictions.

The region’s cool-adapted species are particularly vulnerable as their suitable climate zone shrinks, with lower elevation areas becoming unsuitable. Geographic barriers and altered landscapes limit their ability to move to more suitable habitats, putting these species at risk of extinction.

Currently, nine bird species and subspecies from the Wet Tropics are considered threatened, with five more classified as near threatened by the IUCN. Climate change contributes to these declines through rising temperatures, changing rainfall patterns, and increasing heatwaves. For instance, the population of lemuroid ringtail possum (Hemibelideus lemuroides) has declined by nearly 70% in just over a decade and is now classified as critically endangered.

The impacts of climate change extend to freshwater species. Reduced runoff in headwater streams threatens species like the upland spiny crayfish (Euastacus spp.), which depend on clear, cool water. Climate change affects species indirectly by altering their food supply, predator-prey dynamics, and competition. For example, increased temperatures may exacerbate nutritional stress in ringtail possums, which could, in turn, affect predators like the spotted-tail quoll (Dasyurus maculatus gracilis) that rely on them as a food source.

Although climate change threatens many of the area’s species, the mechanisms by which it is impacting them are poorly understood. Beyond the physiological effects of increased temperature, there are likely interrelated and synergistic effects of climate change, particular to each species, that affect their sensitivity, capacity to adapt, and the range of measures that may assist them.

Cloud forests

Above 900m in elevation, the Wet Tropics mountain-tops form cool, wet cloud forests, known as 'sky islands,' separated from the lower, drier forests. These isolated environments host many restricted, cool-adapted species vulnerable to extinction. Globally, tropical mountain cloud forests are critically threatened by climate change. The Wet Tropics World Heritage Area in northeast Queensland is known to support cloud forests, and houses over 70 endemic species.

Due to their steep environmental gradients and narrow thermal tolerances, these cloud forests are highly sensitive to even small temperature increases. Projections suggest that by 2085, suitable habitat for 37 montane endemics could decline by at least 60%, with seven species potentially facing extinction. These species include Acrotriche baileyana and Hymenophyllum whitei. The latter was rediscovered on Thornton’s Peak but is still at risk.

The mountain-top nursery frog (Cophixalus monticola), found only above 1,100m near Mount Lewis, is critically endangered and requires high soil moisture to protect its eggs. Similarly, the Wet Tropics subspecies of the spotted-tailed quoll (Dasyurus maculatus gracilis), once more widespread, now faces threats from cane toads, cats, and climate change, and is critically endangered.

Conserving these sky islands necessitates addressing additional threats, such as habitat damage by feral pigs and unregulated visits, to enhance species resilience.

Changing fire regimes

Changing fire regimes, often combined with other pressures, threaten about two-thirds of species listed under the Environment Protection and Biodiversity Conservation Act 1999. Climate change is expected to increase the severity and duration of fire weather, leading to more frequent and intense fires. However, specific projections for fire risks to threatened species in the Wet Tropics still need to be made due to complex climate-fire-vegetation interactions.

Historically, rainforests acted as fire barriers. However, they are now increasingly vulnerable due to hotter temperatures, more frequent droughts, and higher vegetation biomass. The regeneration capacity of endemic rainforest species after fire is not well understood. Fires could impact canopy epiphytes (plants that grow in trees and other plants) and seedling populations and allow weed invasion.

Active fire protection, especially in refugial areas, is crucial until we know more about species' fire susceptibility. While fighting fires might be necessary in some cases, using fire retardants or saltwater can harm water quality. Indigenous cultural burning, once common among Rainforest Aboriginal Peoples for landscape management, is being reinstated through collaboration with non-Indigenous land managers to address these fire challenges.

Extreme events

Extreme climate events, rather than gradual changes, significantly impact biodiversity. In Australia, intensified heatwaves since 1950 have led to severe ecological consequences.

• A major heatwave in November 2018 killed about 23,000 spectacled flying foxes, roughly one-third of their Wet Tropics population. Consequently, their conservation status was upgraded from vulnerable to endangered.
• The 2019-20 bushfires, the worst on record, affected 53% of the Gondwana Rainforests of Australia World Heritage Area and 80% of the Greater Blue Mountains World Heritage Area, with long-term impacts on species and ecosystems yet to be fully understood.
• In December 2023, Tropical Cyclone Jasper, and the subsequent extreme rainfall event, caused flooding and landslides on a scale not seen in living memory in the north of the Wet Tropics World Heritage Area.

Severe tropical cyclones, like Jasper, Larry, and Yasi, have destroyed habitats and reduced food resources, leading to altered behaviours and distributions of species like the spectacled flying fox and the tooth-billed bowerbird. As cyclones are expected to become more intense with climate change, the risk to threatened species and ecosystems increases.

The Wet Tropics Management Authority’s Accept, Act, Adapt: Climate Adaptation Plan for the Wet Tropics: 2020–2030 aims to:

• establish regional adaptation planning frameworks
• improve landscape resilience
• support a transition to adaptive communities and industries.