Interactions between pressures and cumulative impacts

Ecosystems and species seldom respond to pressures in isolation, and the most abrupt changes in ecological systems frequently arise from interactions among multiple pressures rather than changes in a single pressure.

Similarly, most threatened species and ecosystems cannot be recovered by managing a single threat. However, many threatening processes affect species by similar mechanisms, such as through the removal or degradation of habitat. For example, 86% of Australia’s threatened species are subject to multiple threats that amount to habitat destruction and degradation, including logging, mining, urbanisation and agriculture, for which the key conservation response is habitat retention and restoration (Kearney et al. 2020). Almost all species require multiple integrated management responses to address their threats (Figure 38).

Figure 38 Number of Australian threatened species that would benefit from different conservation responses

Researchers have recently shown how pressures from global climate change and regional human impacts, occurring as chronic ‘presses’ or acute ‘pulses’ such as extreme events, drive ecosystem collapse. Ecosystem collapse means these places are experiencing potentially irreversible environmental changes, including loss of important species such as dominant trees, and loss of functions such as pollinators (Bergstrom et al. 2021). Local examples of ecosystem collapse can be seen across all Australian and Antarctic ecosystems, although not yet across the entire distribution of an ecosystem type.

Multiple pressures amplify effects on biodiversity in complex and sometimes unpredictable ways, and their interactions pose significant and specific challenges to natural resource management. In addition, the management of some pressures can have the unintended consequence of exacerbating other pressures. For example, in South Australia, red fox control resulted in increases in rabbit populations, which then benefited feral cats (Stobo-Wilson et al. 2020).

The interaction between invasive species and fire is of increasing concern as climate change continues to alter fire regimes (see Changing fire regimes). Invasive grasses such as gamba grass and buffel grass increase fuel loads and fire intensities, sometimes dramatically altering ecosystem structure and function. These species are considered transformer species because of their ability to alter invaded environments by forming dense infestations that increase fire connectivity.

Native mammal declines, particularly in northern Australia, have drawn attention to the potential for fire to exacerbate the impacts of introduced predators. For example, feral cats are more abundant and hunt more successfully in areas that have experienced recent or severe fires (Davies et al. 2020, Legge et al. 2020). Mammals in southern Australia may also be affected by synergistic interactions between fire and introduced predators (Hradsky 2020). Fires typically cause the short-term loss of understorey vegetation, leaf litter, coarse woody debris and tree hollows, all of which provide shelter from predators for native animals.

Case Study Managing interacting pressures to protect tjalapa, the great desert skink

Dr Rachel Paltridge, Kiwirrkurra Indigenous Protected Area Coordinator, Desert Support Services

Tjalapa (also known as tjakura, warrarna, mulymidji, great desert skink or Liopholis kintorei) is a large, orange, communally living skink that occurs in the western deserts. It is classified as Vulnerable due to a decline in range over the past 50 years. The species is of enormous cultural significance, with its own Tjukurrpa (dreaming) songs, sites and stories. It is remembered as a favoured source of meat that would be ‘scaled like a fish’, was efficient to harvest from the communal burrows, was soft for children to chew and like a ‘stick of butter’ with good fat reserves (Kiwirrkurra, Ngururrpa and Martu Traditional Owners).

Key threats to tjalapa are cat predation and inappropriate fire regimes. When burrow systems are burned the lizards become highly vulnerable to predation when they emerge to defecate in their communal latrine and forage for food, and burnt burrows generally become inactive in the year after a fire. Strategic burning to maintain spinifex cover over burrows and cat control (particularly if a fire does occur) are therefore the most important management activities to protect tjalapa.

In 2016, only 12 widely separated locations where tjalapa occurred were known, with 90% of these on Indigenous-owned or Indigenous-managed land. Four new populations have been detected in the past few years, significantly expanding both the known range and the number of individual colonies. The new colonies were found largely as a result of Indigenous rangers learning from other rangers about how to find their burrows, as well as the cultural and conservation significance of tjalapa, at a series of ranger networking events organised by the Indigenous Desert Alliance.

On the Kiwirrkurra Indigenous Protected Area, tjalapa populations are monitored as an indicator of the health of Country, and to assess the effectiveness of traditional fire management and cat control practices. Using traditional tracking techniques, the rangers removed more than 200 feral cats from a 30 kilometre (km) radius around Kiwirrkurra between 2014 and 2020. Hundreds of small fires are lit every year to regenerate food plants and prevent big wildfires, with most fires less than 5 hectares in size.

Each year at the end of summer, the Kiwirrkurra rangers survey 3 transects, each 1 km × 300 m, to map active tjalapa burrows and assess the proportion that have any signs of disturbance from fire, predators or hunters. They also use motion-detector cameras to monitor predator visitation to tjalapa burrows in the spring. In 2021, the rangers mapped 78 burrows across 3 sites, 71 of which were active. The numbers have been gradually increasing over the 5 years of monitoring.

Kiwirrkurra school students help the rangers with their monitoring, and are familiar with tjalapa’s tracks, scats and burrows; where to find it; its threats; and Tjukurrpa stories.