By LINDSAY JOHANNSEN
This is a story about the bad guys winning, going on from my recent letter in these pages.
Buffel continues its slow but steady advance into areas still the realm of native grass varieties.
This constantly occurring process begins with a few wind transported seeds germinating and establishing outpost colonies. Each of these then spreads its seeds locally, expanding their area of influence and initiating further colonies.
PHOTO: Buffel grass has invaded Palm Valley, a jewel in the crown of Central Australian tourism.
And from that point onward buffel simply outcompetes its indigenous neighbours – for space and sunlight; with its ability to survive long dry periods, with its reaction time to storms and showers, with the rapidity of its flowering and seed development (plus the sheer volumes of seed it produces), and with its adaptibility to different situations and soil types. Only heavy clay soil areas and the desert spinifex regions generally seem exempt.
Of further advantage to buffel is its ability to germinate following rainfall insufficient to activate the native grasses. In an example I witnessed in the Jervois Ranges, a light shower on disturbed red sandy loam germinated some buffel seeds. The rain was followed by temperate sunny weather, and the buffel’s species-survival strategy in response to this was remarkable.
As the soil began to dry, each of these seedlings, with just three or four little leaves, quickly threw up and developed a tiny seed head before dying. All of the stems were less than a hundred millimetres in height and none held more than 10 or so seeds.
But there’s more. Buffel responds to rain with new leaves and seed development at any time of year, whereas native grass germination is more season-specific. In fact mid year rains in the Centre will produce little or no grass at all.
Instead it brings up the herbs and ground covers etc native to an area, though exactly which of them it will be on any given occasion and how this is determined is complex and unpredictable.
Each is sensitive to a particular rain event’s nature and timing – was it preceded by frosts, was the rain heavy or light, did it come as cold protracted drizzle or warmer showers, and what type of weather immediately followed?
One rain will bring ground covers, following which a plethora of colourful caterpillars will hatch and begin eating them; another will carpet open areas of soil almost exclusively with succulents or goat’s-head thorn plants or lavender coloured wildflowers or the diabolically pestiferous bogan flea (Calotis hispidula) – though it will not be exclusive; a variety of other plant types will always germinate as well.
And a rain event favourable to one species or another may not be duplicated for a decade or more, leaving newcomers to the area wondering where this or that variety of wildflower or ground cover suddenly came from.
One thing is certain, however: underlying these seemingly random determinations will lie a sound evolutionary principal, a “fair-go” type mechanism whereby each species has an opportunity to flourish and reproduce without being overwhelmed by every other member of the local ground-flora germinating around them at the same time (including the summer-only grasses).
This factor forms part of each species’ long-term survival mechanism as well, where some of its seeds will germinate promptly and some will not, while others will lie dormant in the ground for years, waiting for their biological-clock to wake them.
It is fire, however, that is most benificial to buffel – and its advantage is almost total. (“Almost”, because in order to germinate, certain native species’ seeds require they first be scorched ‒ and scorched; not incinerated.)
Following rain, as the ground dries out, buffel’s leaves and woody seed stems die-off, with subsequent rain producing new growth. And while ever an area remains unburned, this dieback / new-growth / dieback pattern steadily increases a locality’s fuel load ‒ and in particular, its scale-of-fire threat.
Fire has always been present here, of course. Most are initiated by lightning strikes, events which are often followed by rain. And, naturally, a fire in native grass will kill many of the smaller shrubs and sapling trees it encounters.
Even so, in the longer term, survivors and subsequent germinations will usually prove adequate to maintain a given bushland type’s overall integrity. This is due in part to the Centre’s slow-growing tree and shrub species having evolved in concert with its lighter, fodder-type native grasses (an empirical grouping broadly known as “kerosene grass”, due to its vigorous combustibility when dry).
Such is not the case where buffel is concerned. Buffel’s woody stems burn a good deal hotter (allegedly) than the native grasses and certainly burn for much longer. This results in the almost total loss of any seedlings and saplings in a buffel fire’s path, along with a good many semi-mature and mature trees.
More significfantly, buffel’s average fuel buildup and “fire-cycle” period is such that subsequent new-generation individuals have little chance of reaching maturity before another burn is upon them.
Prior to the advent of buffel a buildup of fuel like this rarely occurred. The indigenous grasses are finer and lighter than buffel and, once dry, can be depleted by wind, particularly wind in the weeks following rain. Rain tends to degrade the native grasses when dry and, once dried out again, they become weaker, more fragile, and more susceptible to breakage by foraging stock and removal generally by strong wind.
But it’s the Centre’s grass-eating termite species which are most responsible for the depletion of native grasses. The grasses are harvested at night via fragile temporary mud tunnels, and their ability to denude an area is only marginally slower than that of grazing stock. (I will mention here, too, that I have yet to see any evidence of termites harvesting or consuming buffel grass.)
Currently, buffel’s competitive advantages have seen it either eliminate or practically eliminate all native grass and smaller plant species from many areas it has occupied ‒ the herbs and succulents and ground covers and ferns etc which, under more normal circumstances and following an appropriate rain event, would have briefly populated their own little environmental nooks. And along with these smaller plants, so too their associated microfauna.
But displacement doesn’t stop there. All native species are affected, though few in any beneficial manner. For the greater number it will be a matter of “adapt or perish”, a big ask in most instances.
Regrettably, the conclusions seem inevitable: over the longer term (say 30 to 50 years), that which the constant pressure of buffel’s competitiveness doesn’t displace or kill off, its “fuel-buildup-then-burn” fire-cycle regime eventually will.
As a result, the region’s acacia-scrub woodland and all else it manages to colonise will become – if not wholly, then in broad essence – a buffel grassland monoculture.
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(As a footnote I might add that in and around parts of Darwin and Palmerston a (tropical?) variety of buffel is running rampant (along with three metre gamba grass). This buffel has seed stems two metres tall.)
The sooner we get the buffel grass seed head caterpillar to work the better.
It’s native to Queensland and eaten by many birds and it should thrive and roll back the buffel invasion.
For all the talk of another cane toad, the grub would need a massive environmental downside for it to do more harm that good.
I largely concur with Lindsay Johannsen’s observations about buffel grass; however, another mode of seed spread is via the digestive tracts of herbivores.
I pointed this fact out several years ago, beginning with observations of buffel seedlings germinating in euro (hill kangaroo) scats at Olive Pink Botanic Garden.
I followed this up with a germination trial of fresh euro scats I collected by the Todd River near the Old Telegraph Station – no buffel seedlings emerged but I did obtain couch grass and stinking lovegrass seedlings, both introduced species. There were no native species.
I can also confirm that termites do indeed consume buffel grass, including seeds gathered from the ground surface, but no way near enough to make any impact on the grasses (seed harvesting ants also consume buffel grass seeds).
I’ve taken quite a number of photos of termite activity in buffel grass; and indeed pointed out in an article published in the Alice Springs News over a decade ago that one species of termite that prevails in rocky hill slopes has become particularly partial to buffel grass.
On one damp overcast day at the Olive Pink Botanic Garden I observed (and photographed) termites actively and vigorously harvesting dead buffel foliage and stems during daylight hours. Every buffel clump I checked on the hillside at OPBG had termite activity associated with it, and I believe this works to the mutual advantage of both species but would have significant implications for the natural ecology assuming this situation applies on a wider landscape scale.