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Issue: Direct pressure of human activities on the land - Species introduction and species change

This is an issue under the Land theme of the Data Reporting System.

Why we need to know about this issue

One of the principal human purposes in removing vegetation and other life forms from the land is to make way for the introduction and nurturing of other life forms that are more directly useful to humans. Non-native plants and animals and other life forms can also be introduced by accident or carelessness and survive to establish wild populations. Changed fire regimes can further complicate the mix of native and introduced species participating in altered ecosystems.

Introduced species of plants and animals, both domestic and wild, can place pressure on native vegetation and ecosystems in a number of ways. Introduced vegetation can compete with native vegetation for the same food and shelter. Introduced herbivores, even in relatively low stocking densities and relatively good seasons, can overgraze both native and introduced vegetation because these animals (for example sheep) have been bred for environments where the vegetation was better adapted to close grazing on much deeper soils than most Australian soils. Introduced herbivores can also contribute to land and surface water degradation because of their hard hooves and heavy bodies (cattle and horses) or digging behaviour (rabbits and pigs). On the other hand, introduced species that become naturalised into resident ecosystems also contribute to those ecosystems in a range of ways most of which are, at present poorly understood.

Number of introduced species, and populations and distribution of species are not meaningful as pressure indicators unless there is a demonstrated association with an impact on one or more native species. To demonstrate whether naturalised populations are exerting pressure on terrestrial systems, it is necessary to eliminate any extraneous pressures which may be the common cause of both the proliferation of the introduced species and any contemporary damage to native species. Current research into the both the role and pressures on naturalised species may provide some useful insights into the kind of data that are needed.

Two aspects of pressures from introduced animals that are measurable are: the extent to which the landscape has been altered to accommodate introduced animals and plants; and the extent to which the primary productivity is coping with the consumption of vegetation by introduced domestic herbivores.

Indicators

• LD-01 The proportion and area of native vegetation and changes over time 
  Change in extent of native species is also an indicator for change in extent of introduced (non-native) vegetation species. It may also be a surrogate indicator for distribution of naturalised fauna because naturalised fauna tend to be better adapted than native fauna to introduced vegetation.
• LD-19 Land use and land use change 
  Human land uses generally involve the introduction and production of introduced species and the manipulation of the natural environment (in turn changing populations and distributions of native species), in order to accommodate and nurture those introduced species. The combined pressures of these introduced species and associated manipulations can be complex and vary considerably between different land uses.
  As a pressure indicator this indicator needs to be read in the context of actual or potential pressures known to be associated with each introduced species, overall grazing pressure, and indicators relating to land clearing, erosion, salinity, drought and climate change and fire regimes.
• LD-40 Current research into pressures and contributions of naturalised introduced species 
  To learn whether naturalised populations are exerting pressure on the terrestrial systems that maintain the condition of the land, it is necessary to eliminate any extraneous pressures which may be the common cause of both the proliferation of the introduced species and any contemporary damage to ecosystems. Current research into the both the role and pressures on naturalised species may provide some useful insights into the kind of indicators and data that are needed to inform on this issue.
• LD-20 Total grazing pressure relative to net primary productivity 
  Grazing pressure is a complex issue involving the introduction of non-native grazers and non-native pasture, as well as anthropogenic expansion of native pasture and native grazers. It is one of the principal ways in which introduced species can impact on the land.
  Grazing removes groundcover and nutrients from the land, often land that has already suffered substantial loss of cover and nutrients through land clearing and loss of associated biodiversity. It exposes the land to further nutrient loss through soil erosion. The loss of soil, soil ecosystems, soil nutrients and pasture biodiversity can preclude vegetation (either natural or agricultural) and other biodiversity from re-establishing.
  This indicator measures the pressure of grazing by introduced domestic animals in terms of the biomass available for grazing and therefore gives a broad picture of the area of the continent affected by various degrees of grazing pressure by introduced animals and altered populations of native animals.
• LD-35 Temporal and spatial correlation between changing fire regimes and species change 
  Fire in certain patterns favours some forms of vegetation, and animal life, and destroys others. Intense, widespread and frequent fires have the potential to entirely clear the land so that it provides more or less a clean slate for the colonisation of new species. Fire regimes therefore play a role in maintaining the population and distribution of native species, and change to those regimes have the potential to alter those populations and distributions.
• BD-12 Examples of the impacts of fires on biodiversity 
  The introduction of new species to a location can impact on the fire fuel load, for example, some prolific introduced species may make an area more fire prone by increasing fuel loads, while the high grazing pressure of introduced herbivores can reduce fuel loads.
  Established fire regimes may favour native, fire resistant plant species over introduced plant species. However, changed fire regimes may alter the balance of favour towards introduced species. Complex issues can arise where non-native pioneer vegetation rescues land that has been devastated by fire but then competes with native species attempting to reestablish themselves.
  As there is no continent-wide method of measuring changes in species mix that can be directly attributed to fire across all species and habitats, examples of species that are showing impacts that appear to be directly attributable to fire is at present the only useful indicator of the relationship between fire and species change.
• BD-13 Examples of the impact of grazing on biodiversity 
  Grazing pressure is a complex issue involving the introduction of non-native grazers and non-native pasture, as well as anthropogenic expansion of native pasture and native grazers. It is one of the principal ways in which introduced species can impact on the land.
  Grazing pressure by both introduced grazers removes groundcover and nutrients from the land, often land that has already suffered substantial loss of cover and nutrients through land clearing and loss of associated biodiversity. It exposes the land to further nutrient loss through soil erosion. The loss of soil, soil ecosystems, soil nutrients and pasture biodiversity can preclude vegetation (either natural or agricultural) and other biodiversity from re-establishing.
  Suitable indicators for measuring grazing pressure on biodiversity have not been developed. Research and examples may shed some light on the extent of these pressures.
• IW-37 Examples of carp pressures and measures for removal and/or commercial catch 
  Carp are an example of an introduced species which thrives because of human modifications of the environment but which, in turn, may place pressure of their own on the environment. Examples of pressures from carp, along with either positive or negative changes in these pressures where control or harvesting measures are taken may provide insights into the actual impacts of the animal and the effectiveness of responses.
• IW-38 Cane toad distribution 
  In 1935 cane toads were released throughout cane growing areas in Queensland to control cane beetles. They did not control the beetles but ate large numbers of beneficial insects.
  The cane toad has a large gland behind the head that can exude a poisonous milky substance when the toads are disturbed. Cane toad poison is highly toxic to many animals, including terrestrial animals. The eggs and tadpoles of toads are also poisonous. Predators are vulnerable to the toads. Since introduction the cane toad has increased its distribution. Changes in the extent of its distribution provides some indication of the area where the species could become invasive.
• IW-39 Examples of significant wetland weeds 
  In the absence of detailed data on the distribution and actual impact of various wetlands weeds, examples of how particular weeds can affect the environment are worthy of consideration.
• BD-09 The change in extent of selected nationally significant invasive species 
  Modification of the terrestrial environment, whether for agriculture or urban development of any other human purpose, involves removing resident species and introducing new species. This intentional unbalancing of ecosystems can cause some species in the modified environment to become invasive. While it is difficult, on the basis of any available data, to establish whether and how invasive any species might be in the wide range of environments and ecological communities across Australia, changes in distribution and population of one species may be an indicator of more profound ecological changes. Additionally, where there is a concern that a particular species is behaving invasively, changes in its distribution may signal an increase in area at risk, either from the species itself, or from the environmental modifications that are favouring its expansion.
• BD-10 Examples of native species whose populations have declined where various invasive species have established resident populations 
  Changes in population and/or distribution of either native or introduced species may be indicative of more general changes in land condition, whether the cause of the change is habitat modification, species introduction, or any other pressure. Compiling data on such correlations may also enable the development of studies which control for other pressures and thus provide insight into the actual impact of naturalised species on land condition.

Related issues

• Land - Land condition- Land cover 
• Land - Land condition- Soil stability and quality 
• Land - Land condition- Condition of terrestrial species and ecological communities 
• Land - Land condition- Hydrology 
• Land - Direct pressure of human activities on the land- Soil loss and loss of soil quality 
• Land - Direct pressure of human activities on the land- Land clearing 
• Land - Direct pressure of human activities on the land- Salinity 
• Biodiversity - Pressures on biodiversity- Fire 
• Biodiversity - Pressures on biodiversity- Grazing pressure 
• Biodiversity - Pressures on biodiversity- Invasive species 
• Inland Waters - Response of biota- Invasive species 
• Coasts and Oceans - Direct pressure of human activities on coasts and oceans- Direct pressure of shipping