Sunday, May 16, 2021

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Home Issue 10 Buffel grass threatens butterfly species

Buffel grass threatens butterfly species

By JULIUS DENNIS

Little is known of the Desert Sand-skipper, one of only two butterflies endemic to the arid land of Central Australia, but what is known is that buffel grass could be its demise.

Dr Michael Braby, Associate Professor at the Australian National University and a leading butterfly expert, says that there is “zero” research being done on the skipper.

Despite possibly being on the brink of falling out of the ecosystem, it is not classified as a threatened species by the Commonwealth or the NT Government, leaving it without legislative protection.

The Desert Sand-skipper caterpillars, which can live for years in self-built shelters waiting for rain, have a very particular diet, only feeding on native Enteropogon, also known as windmill grass.

Dr Braby says that Enteropogon “tends to grow in the swales of dunes and along dry river beds,” the front line of the invasion of buffel.

“Because it relies on this species, very specifically this grass, that makes the butterfly quite susceptible to environmental change, and habitat change in particular.”

Just how difficult a situation the butterfly is in is unknown, but the Threatened Species Recovery Hub of the National Environmental Science Program has identified it as one of 26 Australian butterflies at most risk of extinction.

“It’s one of those species, we’re really concerned about that and really needs more research on the ground to figure out what’s the impact this grass is having and how the butterfly is coping,” says Dr Braby.

There may be pockets where the Sand-skipper is persisting on certain riverbeds or protected areas.

Dr Braby says he has found “immatures” of the scarce butterfly “where the grass density is not so high.”

He thinks that these areas “might afford some sort of protection,” from the ever expanding wrath of the buffel grass, but without boots on the ground research it will be impossible to identify or find these havens, if they exist at all.

In February, a paper proclaimed arid land around Alice Springs as one of 19 Australian ecosystems in a state of collapse.

One of the factors of this collapse was a “loss of biodiversity and ecosystem function degradation.”

Dr Braby says that butterflies in general can be a “good indicator” and can tell us “what’s going on in terms of overall biodiversity.”

Both the February paper and the Threatened Species hub say that removal of buffel grass and fire mitigation are key to saving the Desert Sand-skipper and ecosystem as a whole.

Earlier this month, an NTG spokesperson said that the “government recognises that buffel grass can impact upon environmental and cultural values and intensify rangeland fires, alongside posing a heightened risk to biodiversity.”

Despite that recognition, the spokesperson also proclaimed the supposed upsides of the invasive species:

“As a pasture species, buffel grass remains highly valued by cattle producers for being drought tolerant, moderately nutritious and capable of withstanding heavy grazing.

“The extensive root system of buffel grass enables it to bind soil particles; reducing erosion and suppressing dust, which can be a valuable asset in an extremely arid environment.”

Whether the Inland Desert-skipper and the multitude of other native flora and fauna put at risk by the “highly valued” weed feel the same is doubtful.

2 COMMENTS

  1. The turning point for my attitude towards buffel grass (I had grown up as a supporter of it) came in May 1991 when I stopped for a break on the banks of Allua Creek east of Alice Springs on one of my regular “rain gauge” runs as a technical officer of the Rangelands Production Section, Department of Primary Industry and Fisheries.
    Since 1986 I was familiar with this location which was a stretch of riverine ecology virtually untouched by livestock, as it was too far from the nearest permanent watering point.
    When I first saw this spot, the river banks were dominated by tall perennial native grasses, especially curly windmill grass (Enteropogon acicularis), which included amongst its virtues being a valuable species highly palatable for cattle.
    When I stopped for awhile at this site in 1991 I noticed the curly windmill grass had almost vanished, completely replaced by buffel grass – I was stunned at how fast this profound change had occurred in a vicinity unaffected by livestock.
    I realised then that buffel grass was becoming a major problem for the regional environment.
    The susceptibility of Enteropogon grasses to competition from buffel grass is well known.
    For example, monitoring sites and exclosures were established by Bob Winkworth, the first CSIRO scientist permanently based in Alice Springs, during the 1950s and early 1960s; including along the banks of Roe Creek south of town which were dominated by Enteropogon / curly windmill grass.
    During Winky’s last visits to the Centre in the early 2000s he revisited his old sites, accompanied by my father Des Nelson – not a single clump of curly windmill grass could be found along Roe Creek.
    It’s interesting to read about the Desert Sand-skipper butterfly and its association with Enteropogon grasses, I had no knowledge of this until now.
    Coincidentally, I had a long-standing query about the identity of another insect species resolved today (courtesy of AZRI).
    On rare occasions following good rains I’ve sometimes noticed clusters of tiny insects on the undersides of vigorous grass leaf blades, especially on buffel grass.
    All the life-cycle stages are visible – eggs, nymphs and pupae, and the winged adults, looking like a mixed scale / whitefly infestation, and invariably attended by ants attracted by the honeydew produced by these insects.
    Until today, I’d never found anyone who could identify these insects.
    I first recall seeing them in 1983 when I worked at the Horticulture Block at AZRI; and this would likely have been after the major flood of March that year.
    Most often I have seen these infestations on buffel grass but also on kikuyu, and just last week on some sorghum plants – the insects favour grasses with wide leaf blades.
    They do not appear to cause any significant harm to their host plants.
    Only once have I seen them infest a native grass species, which happened to be a well-watered clump of Enteropogon / curly windmill grass at Olive Pink Botanic Garden when I was working there in 2007.
    I deduced from my infrequent observations over nearly 40 years that this insect species is likely to be introduced into Central Australia.
    Turns out I’m correct – the insect is known as sugar cane whitefly.
    The identification of this insect species allows me to surmise how it arrived here – the whitefly was probably accidentally introduced by senior horticulture technical officer Frank McEllister who grew rows of sugar cane in the early 1980s as windbreaks for trial crops at the Horticulture Block at AZRI.
    Buffel grass has proven to be an excellent host enabling sugar cane whitefly to persist around Alice Springs for many years.
    Frank McEllister is the first person I recall being critical of buffel grass as it was a major weed that we had to control at the Horticulture Block.
    Frank often pointed out that crops provided a far greater economic return per unit area of land compared to beef cattle, so from his viewpoint the benefits of buffel grass for pastoralism was far outweighed by its cost for weed control in horticulture.
    Ironically, the AZRI Horticulture Block was the same location that the CSIRO conducted the pasture species evaluation trial in the early 1960s that demonstrated how successfully buffel grass could grow here.
    Just possibly, Frank McEllister may have unwittingly introduced the factor that may lead to biological control of the buffel grass he once loathed at that very same site.
    Sugar cane whitefly doesn’t cause any direct deleterious impacts on its host plants but conceivably could become a vector for the spread of a viral disease, should one turn up.
    In this era of climate change, ecological imbalances and pandemics, the possibility of this occurring cannot be ruled out.

  2. This mentions that the host plant is Neurachne tenuifolia (Palmer and Braby 2012).

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