Does artificial water point closure lead to decreases in grazing pressure in arid and semi-arid zones?

Introduction

European settlers introduced artificial water points to the mulga lands of southwest Queensland nearly 200 years ago (Seabrook et al. 2006; Fensham and Fairfax 2008) to support domesticated grazing animals.

Where previously, the limited number of natural water points in arid and semi-arid zones restricted herbivore density (James et al., 1999) the provision of artificial water points has transformed this landscape (James et al., 1999; Fensham and Fairfax 2008). Population increases have been observed in domesticated sheep (Ovies aries), cattle (Bos taurus, Bos indicus) and goat (Capra hircus), but also in native kangaroo populations (Macropus spp.) (Fensham and Fairfax 2008).

Although critical to economic growth at the time, grazing regimes and overabundance of herbivores have led to land degradation, habitat destruction and biodiversity declines in the mulga lands (Lavery et al. 2018).

Recognising the influence of water provisions on grazing intensity, Fensham and Fairfax (2008) analysed threshold distances from drinking water for sheep (3km), cattle (6km) and red kangaroos (M. rufus, 7km). This research suggested that ‘water-remote’ areas existing outside these threshold distances would be ‘the most effective means of achieving grazing relief’.

Idalia National Park in the mulga lands of southwest Queensland has undergone several landscape changes and only recently designated a national park (Queensland National Parks and Wildlife 1998; Fensham and Fairfax 2008). These shifts in management strategy and land-use make Idalia an ideal site to observe the influence of water-remoteness on grazing pressure.

This study simulates how the availability of water (through both natural and artificial water points) and changes in dominant herbivores have altered vegetation suitable for grazing over time.

Methods

Using ArcGIS, the vegetation of Idalia National Park was analysed under four different scenarios (Fig 1). The threshold distances of herbivores (Fensham and Fairfax, 2008) was simulated by manipulating the presence / absence of artificial and natural water points illustrating total area (ha) available for grazing and total area (ha) considered water-remote.

Scenario 1 – Pre-European landscape (circa 1750): assumes large macropods provided grazing pressure and permanent natural waters were the only water source;

Scenario 2 – Original pastoral landscape (circa 1900): assumes macropods were controlled, cattle were the dominant herbivore, and presence of both natural and artificial sources of water;

Scenario 3 – Early national park landscape (circa 1990): assumes cattle removed; macropods were not controlled and could penetrate the boundary fence; presence of bothnatural and artificial sources of water.

Scenario 4 – Recent national park landscape (present day): assumes all artificial water- points on the park have been fenced but neighbours’ artificial water-points can have an influence. This also continues to assume that macropods can penetrate the boundary fence.

Scenario 1: 
 Pre-european landscape 
 (circa 1750)

Scenario 2: Original pastoral landscape 
 (circa 1900)

Scenario 3: 
 Early national park landscape 
 (circa 1990)

Scenario 4: Recent natural park landscape (present day)

Water Points

Natural

Natural & Artificial

Natural & Artificial

Natural

Dominant herbivore

Macropods

Sheep & Cattle

Macropods

Macropods

Grazing range

7km

4km

7km

7km

Fig 1. The four different scenarios used to assess total area (ha) available for grazing and total area (ha) considered water-remote.

Results

As illustrated in Fig 2, grazing availability across all major vegetation types on Idalia National Park increased with the introduction of artificial water points. The reduced range of dominant herbivores (sheep and cattle, 4km) is accounted for with observed increases in grazing availability between scenario two and three where sheep and cattle are removed and macropod culling has ceased.

With the reduction of available water points simulated in scenario four, grazing availability starts to return to the pre-european landscape levels of scenario one. However, land available for grazing in some vegetation types (particularly Wooded Downs, Escarpments and Footslopes) are still well above pre-european landscape levels.

Fig 2. Percent of total area (ha) of the seven major vegetation types of Idalia National Park suitable for grazing or considered water-remote under four different scenarios of grazing pressure.

Discussion

Idalia National Park is primarily open plains, not only the preferred habitat of native kangaroos (Macropus spp.) but being generally flat (with slopes < 3%), it is also ideal for pastoral activity. However, with low and variable rainfall, domesticated sheep (O. aries) and cattle (B. taurus, B. indicus) require the provision of artificial water points to survive in arid and semi-arid environments (James et al., 1999; Hunt et al. 2007; Munn et al. 2013) making them an important management tool (Underhill et al. 2007)

Assuming the threshold distances asserted by Fensham and Fairfax 2008, the trends observed in this analysis would seem to support the influence of artificial water sources on grazing pressure.

These affects are most pronounced in the wooded downs vegetation types but are observed to a lesser extent in the escarpments and footslopes. This is likely explained by the nature of the vegetation itself as they are home to long-lived perennials like brigalow (Acacia harpophylla), boree (Acacia pendula) and gidgee (Acacia cambagei) that are highly adapted to regions of low and variable rainfall (Fukuda et al. 2009)

The limited affects observed in the barren plateaux and mulga/shrubby tabletops vegetation types may be due to their location on ranges, with topography and fertility a barrier to grazing pressure (Wilson and Taylor, 2012).

The increase in grazing availability following installation (and removal in scenario four) of artificial water points demonstrates the influence on the distributions of native kangaroos (Macropus spp.).

Although Fensham and Fairfax (2008) assert a threshold of 7 km from drinking water, red kangaroos (Macropus rufus) are capable of movements up to 30 km following rainfall events (Underhill et al. 2007). This is of particular concern with the scarcity of water-remote landscapes markedly increasing species distribution and grazing potential (Fensham and Fairfax 2008).

Although the trends observed in Fig 2. seem to support the influence of artificial water sources on grazing pressure, several assumptions limit the scope of this work.

With regard to vegetation types, each has been assumed as equally accessible to herbivores and constant in terms of flora available for grazing. The water points (whether natural or artificial) are assumed accounted for and in a condition suitable for use. These violations may have led to an overestimation of land available for grazing and the true range capability of herbivores in this analysis.

The effects of climate and rainfall variability in this environment on both herbivores and vegetation is well documented (James et al. 1999; Underhill et al. 2007; Fukuda et al. 2009) but largely absent from this analysis. It would be worth considering how climate and rainfall influence habitat productivity and how this could be used as a determinant of species range capabilities (Sharp 2009).

There has also been no consideration of species absent from Fensham and Fairfax (2008) analysis which ignores the complexity of this ecological community. It would be worth considering the roles of exotic herbivores (eg. horses, goats and pigs), native critical weight range mammals (eg. Numbat) and exotic predators (eg. feral cats and red foxes) to name but a few. These species perform critical roles in competition and in distributing the seeds of many native plants (Hayward et al. 2015).

Conclusion

The influence of artificial water points on grazing pressures in Idalia National Park is clearly complex but it is clear that artificial water points could potentially provide a useful management tool for improving grazing disturbances, herbivore population control and restoration of native flora.

The full potential of artificial water point closure can not be realised without experiments of greater spatial and temporal scale and a better understanding of the complexities of vegetation-herbivore interactions.

Further research should also consider the influence of artificial water sources on adjoining properties and their influence on distribution.

The trends identified in this analysis should be taken as indicative rather than definitive, all assumptions and study limitations should be considered, and more comprehensive studies would be necessary to inform the implementation of management strategies to return Idalia National Park to a sustainable grazing regime that best represents natural grazing.

References

Fensham, R. J., and Fairfax, R. J., (2008) Water-remoteness for grazing relief in Australian arid- lands. Biological Conservation, 141, 1447–1460.

Fukuda, Y., McCallum, B. H., Grigg, G. C. & Pople, A. R., (2009) Fencing artificial waterpoints failed to influence density and distribution of red kangaroos (Macropus rufus). Wildlife Research,36, 457–465.

Hayward, M. W., Aline Si Lin Poh, B. & Cathcart, A., (2015) Numbat nirvana: conservation ecology of the endangered numbat (Marsupialia : Myrmecobiidae) reintroduced to Scotia and Yookamurra Sanctuaries, Australia. Australian Journal of Zoology, 63, 258– 269.

Hunt, L., Petty, S., Cowley, R., Fisher, A., Ash, A. & MacDonald, N., (2007) Factors affecting the management of cattle grazing distribution in northern Australia: preliminary observations on the effect of paddock size and water points. The Rangeland Journal, 29, (2),169-179.

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Lavery, T., Pople, A & McCallum, H. (2018) Going the distance on kangaroos and water: A review and test of artificial water point closures in Australia. Journal of Arid Environments, 151, 31-40.

Munn, A., Dawson, T., McLeod, S., Dennis, T. & Maloney, S., (2013) Energy, water and space use by free-living red kangaroos Macropus rufus and domestic sheep Ovis aries in an Australian rangeland. Journal of Comparative Physiology, 183(6), 843-858.

Queensland National Parks and Wildlife (1998) Idalia National Park, Mulga Lands Biogeographic region – Management plan. Queensland Government, Department of Environment.

Seabrook, L., McAlpine, C. & Fensham, R. (2006) Cattle, crops and clearing: Regional drivers of landscape change in the Brigalow Belt, Queensland, Australia, 1840–2004. Landscape and Urban Planning, 78, 373-385

Sharp, A., (2009) Home range dynamics of the yellow-footed rock-wallaby (Petrogale xanthopus celeris) in central-western Queensland. Austral Ecology, 34, 55-68

Underhill, S., Grigg, G. C., Pople, A. R., and Yates, D. J. (2007). A physiological assessment of the use of water point closures to control kangaroo numbers. Wildlife Research 34, 280–287.

Wilson, P. & Taylor, P. (2012) Land Zones of Queensland. Queensland Herbarium, Brisbane.