The interactions between pressures can result in cumulative impacts, amplifying the threat faced by the Australian environment.
There is increasing evidence that pressures interact in complex ways. For example, land clearing removes natural habitat and typically replaces it with agricultural, urban or industrial development, which may bring additional pressures such as grazing or pollution. In addition, remnant vegetation after land clearing is often fragmented and isolated. Fragmented woodland landscapes have been shown to have more vertebrate pests than intact woodlands (Graham et al. 2012).
Evidence has emerged during the past 5 years that the greatest impact on mammals in northern Australia comes from a combination of predation by feral cats, fire and grazing. Both fire and grazing regimes in northern Australia have intensified substantially in recent decades in ways that have made grass communities less complex and more open, creating conditions that are favoured by feral cats and could contribute to the decline in native mammals (McGregor et al. 2014).
Other interactions among pressures include those between invasive plants—particularly pasture grasses—and fire, which is part of a positive feedback loop. In this situation, fire encourages growth of invasive grasses, which, in turn, provide more biomass and reduce the time between fires. In coastal and marine environments, metal pollution has been shown to encourage the growth of non-native marine invertebrates in ports and harbours.
Climate change is predicted to generally exacerbate existing pressures. Climate change is affecting the viability, distribution and occurrence of native species. It is well established that this is a major factor that will result in, among other things, some native species migrating to seek more favourable conditions and species contracting to refuges. Climate change is also likely to affect the viability, distribution and occurrence of invasive species. The large number of introduced plant species in Australia may become invasive if changing climatic conditions favour them.
Because climate change will enhance existing threats, there is general consensus that the capacity of the environment to adapt to climate change will be improved if other existing threats are addressed or ameliorated.