Unit
Explore SolutionsGenies AdviceGenies MapsGenies LibrarySaltDeck Cards
Unit 1 - What's in it for me?
Unit 2 - Saltland Basics
Unit 3 - Can I trust the technology?
Unit 4 - Plant and animal performance
Unit 5 - Sheep, cattle and conservation
Unit 6 - Do the $$$'s stack up?
Unit 7 - The saltland toolbox
Site Assessment
Solution 1: Exclude grazing
Solution 2: Volunteer pasture
Solution 3: Saltbush
Solution 4: Saltbush & Understorey
Solution 5: Tall Wheatgrass
Solution 6: Puccinellia
Solution 7: Vegetative grasses
Solution 8: Temperate perennials
Solution 9: Sub-tropicals
Solution 10: Legumes
Solution 11: Revegetation
Solution 12: Messina
Solution Explorer
Genie's Advice
Genie’s Maps
FAQ
NSW
SA
TAS
VIC
WA
Farmer Stories
Case Studies
Film Clips
Research Reports
International Salinity Forum
SALTdeck Cards
Published Products
SALT Magazines
Photo Gallery
Saltland Pastures Association
Farmer Stories
Case Studies
Film Clips
International Salinity Forum
Research Reports
NDSP Archive
Saltdeck
Published Products
Photo Gallery
Saltland Pastures Association
Catchment Management Plans
Farmer Stories
Case Studies
Published Products
Photo Gallery
Research Reports
Genie Film Clips and YouTube
Catchment Management Plans
Saltdeck Cards
Saltland Pastures Association
NDSP Archive
Salt Magazines



UNIT 5

Sheep, Cattle and Conservation

 

5.3  Conservation issues

NextPrevious

While there is a strong body of scientific evidence to support the production and economic benefits from saltland pastures, there are few studies that have attempted to quantify the extent to which saltland revegetation might contribute to conservation. It makes intuitive sense that a revegetated saline area would be better for the environment than a bare, saline scald, but quantifying the benefits is not easy.

The ecological benefits from better management of saltland should be expressed through improved water management, reduced salt export, increased biodiversity and improved landscape function. Improved groundcover is a key element in providing both improved conservation and amenity outcomes.

The information in this section is largely drawn from the Sustainable Grazing on Saline Land (SGSL) program, the only national program to seriously examine environmental outcomes from better management of saline land.

Top

Salt & water movement

During the SGSL initiative, salt and water movement was studied at several research sites across southern Australia. When combined with other knowledge, we can now conclude:

  1. Saline sites can contribute very significantly to the export of salt from a catchment. At one intensively monitored site in NSW, the saltland area was approximately 2% of the sub-catchment, but contributed 11% of the total run-off and virtually all the salt that was being exported from the catchment. For more information,see Integrated Gumble Site Report.
     
  2. Saltland pastures can have a significant effect on local hydrology (ie salt and water movement), primarily because there is an increase in evapo-transpiration under well managed saltland pastures compared to untreated controls. This results in a reduction in waterlogging and average soil moisture content above the watertable in the saltland pasture relative to neighbouring un-pastured saltland. In addition, there are clear indications from research that under favourable circumstances (water table shallow but not overly saline) saltbush, tall wheatgrass, and possibly other perennial saltland species, can draw directly from the groundwater and therefore lower the watertable.
     
  3. As a result of the lower water content (and possibly lower watertable), the salt content of the upper soil layers can be reduced by leaching, making sites potentially more suitable for under-storey species that are less salt-tolerant but more productive and nutritious. For example, Michael Lloyd (farmer from Pingaring WA) experienced a major rainfall event (140 mm in two days) over a dense stand of saltbush in January 2006. The watertable at this site rapidly increased by 1.6 m as a result. However, evapo-transpiration by the dense saltbush was such that after 6 months, the watertable had been drawn back down to levels before the event (about 2.1 m – see graph below). The salinity of the groundwater across the site varied between 40 and 100% of the salinity of seawater.

    Figure 5.1

    Figure 5.1 – Watertable depth under a saltbush and under-storey pasture in WA.
     
  4. Intuitively, it would be expected that trees would use more water (soil water and from the watertable) than pastures if the groundwater was not so saline as to prevent roots from accessing it. Direct comparisons between saltland pastures and trees are rare, but work in central NSW has confirmed that trees on saltland can increase water use and lower the watertable which should dramatically reduce surface run-off and salt export from saline sites. For small sites, where conservation and amenity are more important to the farmer than pasture production, trees and shrubs as part of a revegetation mixture are probably a better option than pasture species alone. There are limits to the salinity of the groundwater that plants can use: for trees this limit is around 30% of the salinity of seawater, but for highly salt-tolerant plants like saltbush, the limit is more like 100% of seawater. All plants use non-saline water first, so that watertable drawdown will really only occur in times when conditions are hot and dry. Also, it is the leaves that do the transpiring so saltland pasture plants that have been grazed heavily in summer won’t have many leaves to use up the water.
     
  5. Researchers at SGSL sites in both NSW and WA detected an increase in salt export following the establishment of saltland pastures – despite the fact that surface flows from the sites were reduced in volume. It is possible that site preparation and sowing exposed more salty soil to seepage and runoff water. At the NSW site, this effect was greatest in the first year, moderate in the second year, and by the end of the third year cumulative (3 year total) salt export from the pasture plot was no greater than the control. The scale and longevity of this increase in salt export are likely to be very site and climate specific, and it is complicated by the fact that concentrating and channelling the surface water through a flume (so the volume and salt content can be measured) creates its own ‘erosion’ effect that would not occur in a ‘normal’ paddock. The lesson is that minimal site disturbance, although sufficient for good pasture establishment, should be the aim to maximise environmental benefits from establishing a saltland pasture. 
Top

Biodiversity

The health of an ecosystem is hard to asses in total, so it is often quantified using indicators of biological diversity. For example, stability and health can be related back to a greater diversity in the soil, plant and surface organisms, which in turn provides a more stable food chain. The SGSL initiative used a combination of plant species diversity and arthropod diversity to assess the biodiversity associated with saltland pastures, and landscape functional analysis to assess the soil surface conditions.

While biomass production is the most critical element in saltland pastures, plant composition is also important as plant diversity may improve the ability of the system to adapt to or cope with changes (in climate or local salt and water impacts) over time. SGSL research at Yealering in the WA wheat/sheep zone compared an untreated control with an improved saltland pasture consisting of saltbush in rows, with a range of annual pasture species sown as an under-storey. The results (Table 5.1) show that the revegetated plots had more plant species than the unimproved plots, plus a greater proportion of the plant species in the revegetated plots were native and had a perennial life cycle to increase water use over summer. As a bonus, the improved pasture produced 7.7 t/ha compared to the 1.4 t/ha from the control. This is an excellent example of where both production and biodiversity were winners.

Table 5.1 Plant diversity and plant biomass production from unimproved saltland and an adjacent revegetated plot in Yealering, WA in spring 2005.

 

 Unimproved saltland

Saltbush and sown under-storey

 

# species

Biomass
(kg DM/ha) 

% of biomass

# species

Biomass
(kg DM/ha) 

% of biomass

Legumes

2

72

5

8

4735

61

Halophytes*

0

0

0

2

704

9

Grasses

3

1181

84

4

1953

25

Forbs

6

150

11

4

337

4.4

Native

1

42

3

3

719

9

Exotic

10

97

1361

15

7010

91

Perennial

0

0

0

2

704

9

Annual

11

1403

100

16

7025

91

TOTAL

11

1403

 

18

7729

*Halophytic biomass was taken as leaves and small stems (edible portion) of saltbush, with woody stems excluded.

Arthropods associated with agricultural soils have an important role in food chain dynamics, so studying the impacts of saltland regeneration on these animals should give a good indication of overall biodiversity. In the SGSL initiative, pitfall traps were used to determine the number and diversity of arthropods from saltland pasture sites.

In total, 60 pitfall trapping ‘events’ were collected (season × plot), sorted and fully identified for inclusion in subsequent analyses (see Table 5.2). Pitfall trap samples were first sorted into Order and then into lower-level taxa such that each taxa could be assigned to a single ‘functional group’ (detritivore, herbivore, omnivore, predator or parasite). From the total pool of samples, invertebrates from 29 Orders were identified and sorted into 144 taxa. Between 20 and 23 Orders and 64 and 80 taxa were represented at each site (Table 5.2). In all, 42 taxa were present at only one site; 36 taxa were present at all sites. Sites that had significant levels of plant litter present at the soil surface (NSW and Victoria) had higher abundances and biomasses of invertebrates because of a preponderance of springtails (detritivorous collembola). Native vegetation remnants also tended to show higher levels of invertebrate biomass, perhaps due to more complex vegetation structure. Also noteworthy is the dominance of predators in the arthropod fauna of the WA sites.

Table 5.2. Invertebrate abundance and richness at each project site.

Project

No. of individual
invertebrates

Biomass of
invertebrates (g)

Order-level
richness

Taxa-level
richness

No. of
endemic taxa

NSW (Gumble)

105,2478

 782.4

20 

80

7

VIC (Hamilton)

48,033 

 330.1

20

64

6

SA (Mt Charles)

10,211

 107.2

21 

79

13

WA1 (Tammin)

57,238 

 106.8

23

72

WA2 (Lake Grace)

17,368

 75.0

23

72

9


Saltland pasture sites clearly contain a rich invertebrate population, but differences between treatments were difficult to detect, probably because of the extreme variation that occurs across saltland sites, and the size of plots in SGSL was very large (at least 1 hectare to allow grazing). The results from studies on microbial biomass and microbial respiration have shown that there are extreme differences between vegetated patches and bare patches even in very close proximity, so on saline sites, invertebrate biodiversity is also likely to be extremely variable.

In conclusion, salinity itself has an overall negative impact on biodiversity, especially at the extreme of bare salt scalds. SGSL research indicates that saltland pastures can help reverse some, but not all of that impact.

Top

Landscape function

Saltland can be very fragile, and incorrect management will cause a breakdown of the ecological systems making such sites especially susceptible to water and wind erosion.

“Landscape Functional Analysis” (LFA) was used at SGSL sites, based on an assessment of the soil surface to determine the stability (against erosive forces), infiltration (ability to absorb and retain soil water) and nutrient cycling (the efficiency of organic matter recycling back into the soil).

The research showed that while all salt-affected land is likely to have reduced ‘landscape function’, remnant vegetation still provides a benchmark against which saltland pastures can be assessed. Both saltland pastures and control (or volunteer) pastures had quite high values for landscape function where there was good groundcover, and low values where there were bare patches. The extent to which any treatment (saltland pasture, trees and shrubs, or volunteer species) can revegetate bare soil areas and provide groundcover is a good indication of landscape function.

At a smaller scale, the SGSL research sites also measured microbial biomass and microbial respiration which are very important for nutrient cycling and soil stability.

Averaged across all pasture plots the microbial biomass was 28 mg microbial carbon/100g soil. Western Australia had the lowest average at 15 mg and Victoria had the highest at 37 mg per 100g of soil. In contrast, the scalded areas were much lower – when averaged across all sites, the microbial biomass was 4 mg whilst the remnant vegetation areas averaged 17 mg.

It is unclear whether the lack of microbial activity at the scalded sites is a cause of reduced plant cover or a consequence, however it may be that reduced soil microbial activity is a factor limiting success in sowing saltland pastures.

Top

Groundcover

The key to many of the environmental benefits from revegetating saltland is groundcover – for reducing surface soil evaporation, for protecting the soil from erosion, and as the basis for floral and faunal biodiversity.

Unless fenced off, saline sites are almost always excessively grazed as livestock seek the salty material and often lick the salty soil surface. Sheep especially overgraze saline sites and often camp on them over summer because the soil is often relatively moist and cool. Under conditions of uncontrolled grazing, groundcover will always be low (or even absent) from salty sites.

The differences between vegetated and non-vegetated sites, even within a single saltland area, can be extreme. Data from the SGSL sites have shown that when soil salinity increases and/or in the absence of vegetation, soil microbial activity and biomass are reduced, being almost zero (lowest ever recorded by the laboratory) in soil from bare saline sites.

For sites of equal salinity, where vegetation is present the microbial activity will be about 10 times higher than for bare ground, but even with vegetation it will still be substantially below non-salt-affected pastures. These data though do not indicate whether lack of groundcover is the cause of the reduced microbial activity, or a result of it – however, the link between groundcover and soil health on saline sites is clear.

As demonstrated in the SGSL research and on-farm sites, groundcover can be surprisingly easy to re-establish. Once grazing is controlled, saline sites often produce a surprising amount of utilisable feed from volunteer species. Across the SGSL sites, the control plots (grazed conservatively) produced less than sown saltland pastures, but achieved about 60% of the feed that would be expected from adjacent, non-salty land. Farmers in SGSL reported similar gains from rotational grazing alone, when salty sites were not fenced off from larger paddocks.

As an example of how fencing and conservative grazing can increase groundcover in a low cost way, the control plots at the SGSL site in NSW started (spring 2003) with 44% bare ground. That reduced to 37%, 20% and 15% between spring 2004, spring 2005, and June 2006 respectively.

In conclusion, groundcover is vital for sustainable management of saltland and can be achieved through active revegetation, or by simply fencing off saline sites and grazing them conservatively.

Top

Weeds & Weediness

There are inherent conflicts of interest between the introduction of new plant species for productive purposes (including salinity mitigation) and the potential for such species to become significant weeds in the future. Olives, radiata pine, tagasaste and pasture grasses such as phalaris and perennial veldt grass are all examples of productive species that are currently invading natural ecosystems. In fact, the majority of Australia’s new weeds originated from deliberate introductions.

Environmental weeds invading bushland and watercourses are a major threat to biodiversity, displacing native flora and degrading habitats for native fauna. The weediness issues relate to both introduced and to translocated native species (such as Acacia saligna from WA which is proving ‘weedy’ in the eastern states). Perennial vegetation plays a key role in tackling dryland salinity, but we must make sure that in solving one environmental problem we don't cause another.

In addition, the risks associated with weed invasion from saltland revegetation have to be assessed against other options, including doing nothing. In fact, because saltland pastures have to be established into a hostile environment, to persist and be productive, they must have some ‘weediness’ characteristics. Potentially invasive species (such as kikuyu, couch, saltwater couch or tall wheatgrass) should not be planted near (especially upstream of) native areas or wetlands where the potential for invasion is higher.

Grasses pose a much greater risk than legumes (which are less salt tolerant), and tall wheatgrass has been identified as a particular threat in some regions, such as the higher rainfall areas of South Australia Tasmania and Victoria where wetlands may be at risk. However escapes have been largely confined to roadsides and management techniques have been devised to minimise the spread. Grazing is an important part of reducing the spread, so tall wheatgrass should not be included in revegetation mixtures unless it can be prevented from setting seed.

Top