Regular commentator at this blog Ian Mott sent me the following email:
Hello Jen,
We have all grown accustomed to the notion that it is the removal of trees from the landscape that causes salinity. But recent research from the Argentine Pampas indicates that the addition of trees to a natural grassland can also increase the salinity of groundwater flow systems (GFS).
This could have major implications for the management of salinity in the Murray Darling Basin, particularly in rangeland areas where major thickening events have taken place or where existing small clusters of forest have expanded onto grassland ecosystems.
The study, by Esteban G. Jobbagy and Robert B. Jackson, published in Global Change Biology compared 20 paired plots of forest and grassland and found a significant increase in groundwater salinity under the forested plots. "Afforested plots (10-100 ha in size) showed 4-19-fold increases in groundwater salinity on silty upland soils but less than twofold increases on clay loess soils and sand dunes."
While this study has been limited to planted forest plots on previously grassland ecosystems, the same causal factors are at play whenever forest vegetation expands on grassland. And it logically follows that the same causal factors will be at play when, for example, a 10% canopy woodland thickens to become a 60% canopy forest.
Jobbagy & Jackson have concluded that "Soil cores and vertical electrical soundings indicated that ...salts accumulated close to the water table and suggested that salinization resulted from the exclusion of fresh groundwater solutes by tree roots."
To which the average farmer would say, "Well, they would do that, wouldn't they".
The extensive, 1400 plus, rangeland sample plots done by Bill Burrows confirm that more than 60 million hectares of rangeland in Queensland is subject to thickening at an average rate of circa 0.25m2 increase in basal area per hectare. There is a further estimated 30 million hectares in NSW. And there are also numerous landholder reports of properties that had only 3,000 ha of Gidgee in the early 1900's but have in the order of 50,000 ha today as a result of major encroachment onto grassland.
And this poses an interesting question for the publicly funded anti-salinity industry and the policy arms that have focussed so much public attention on the removal of trees as salinity causal agent. If the lowering of a water table by excess bore irrigation can be widely recognised as a causal factor in increasingly brackish ground water resources, why has it taken so long to recognise that a similar lowering of a water table by the addition of trees can produce the same result?
It certainly invites the question, is there any similar research conducted here in Australia?
Clearly, the political exploitation of salinity appears to be sinking deeper and deeper into murkier water.
Regards,
Ian Mott
u ppl need a life
The early artists used softer tones and light and the bush was more luxuriant - more like a European jungle with muscular darkish skinned Europeans.
Eg George Pitt Morrison, Conrad Martens, Capt Arthur Phillip
Hmm, why the ducks? in 300 words or less. That was a cold waterfall massage, Phil, the best you can get without stiletto heels (so they say).
Hard to pin down on the cause of thickening. The fire creates the seed bed for germination and also reduces competition for soil moisture when the seedlings need it most. And this is the same outcome produced by over grazing. Both create the circumstances for increased seedling growth.
But it seems to be the following fire that used to burn off the successful saplings and the absence of that following fire that enables the thickening process to become an established part of the landscape. And of course, the follow up overgrazing event will only remove some of the successful saplings, not all.
But the interesting thing about pasture cover and water yield is that the improved yield from a shift from full pasture to bare soil is usually even greater than the yield improvement from a shift btween forest to pasture.
I am not certain what research has been done by the CRC for catchment hydrology on this (and no time to look now). But the ever trusty DNRM Water Fact Sheet W24 suggests some generalised indications that at Warwick (660mm RF);
1 heavily timbered land will yield 0.04 MgL/ha,
2 natural grassland will yield 0.13 MgL/ha, while
3 bare ground will yield 0.47 MgL/ha.
And this suggests that if we really want to get our heads around catchment yields and sustainability issues then we need to assess past yields from fire mosaics, pasture depletion (bearing in mind that most pastures will be depleted at the end of a dry season) tree clearing, regrowth and thickening and crop water use.
And after we have done that we can start to get a handle on salinity changes etc with a view to managing catchments. In part, that could include even increased clearing to restore yields from parts of the catchment that have undergone yield depletion effects. And it could include increased ground water irrigation to lower water tables that have risen for other reasons.
For cripes sake. A cold waterfall shower and Ian's gone hyper. (hope you didn't use soap !)
Drysdale painted what he saw when he checked out the 40s droughts. He didn't write a letter to Nature nor do a report. Checks out well with the land condition reports of the time.
Very detailed CSIRO work show shows cows are much worse than tanks in the Burdekin (3-5x the sediment). Note I haven't enetred into what it does nor say that there have not been big pulses in the past.
And why does vegetation thicken - pls don't say climate - you know it's fire. Why do we have less fires (a) they're not lit as it's perceived to be risky if no followup rain (b) they're put out - firebreaks and fence-lines (c) not enough grass fuel !!
And if it's so bad - why have land values gone up?
Slip away for some vitamin F(farm) and indulge in the perfect massage by waterfall and look what you guys do. I accept the pictures, Taz but they are self selected by the artist. They have anecdotal value the same as James Cooks reports that, when the smoke cleared, one could see 2 or 3 miles inland through the woodlands at Botany Bay and earlier along the coast at Woollongong.
Ditto the original description of Melbourne as a very wide open paddock with few trees.
So the whole picture is muddied by the fact that the first removal of trees in those open landscapes would have had only limited impact on run-off and groundwater flow systems because grass was already the dominant vegetation.
It has often been said that over grazing has caused the subsequent thickening of trees but this is a rather loaded value statement. Any reduction in the leaf area of grass will reduce the pasture's capacity to transpire and tend to favour the species that have not been eaten.
And lets face it, what is the difference between a pasture that has been eaten bare and a pasture that has been burnt bare? Both produce bare ground but the dark ash will produce earlier soil warming and greater soil microbial activity. Both produce a marked temporary reduction in transpiration capacity and therefore produce similar effects in retaining soil moisture for longer so that more of the next rainfall event goes to runoff or recharge.
And given that only 2% of our land area is cultivated, we can conclude that the area, scale and duration of exposed mineral soil today is only a fraction of the historical firestick farming level. So how can we describe modern farming as unsustainable when a greater level of soil exposure maintained a modified ecosystem for 50,000 years?
And this is where Drysdale and his wide brown land come in. In part, it was more artistically cool to "discover" the worst views of the landscape and represent them. The best views were already being seen as sacharine and twee.
But the other part was that the scale of the best and worst views became larger and more visible to the outside observer like Drysdale. And unlike their country cousins, the urban art viewer was more inclined to take a single representation of a dynamic system as "the" single truth rather than a snapshot of part of a cycle.
But the overall truth? Bob Carter's coral cores at the moth of Queenslands largest river, the Burdekin, indicate that the worst silt flows took place before any significant clearing had taken place while the lowest silt flows took place during the WWII drought years when the river didn't flow at all. Bob could explain much better than I.
And the ocean floor mud cores at the mouth of the Murray would also have some interesting things to say about the current state of the Murray Darling basin. But I guess that is why they haven't been funded yet.
In a nutshell, we have no chance of finding workable solutions to any environmental problems untill we can trace the detailed path that has led us to this point.
By the stringent prescriptions against over grazing, for example, we may be departing from an historical level of firestick mosaiced bare earth that is reducing stream flows, reducing aquifer recharge, increasing the spread of wildfire and thereby increasing the size of other areas of bare earth that produce increases in stream flows and recharge in those other areas.
We cannot define a duty of care for either public or private tenure until we know the original state, the historical range of variation and the relationships it involved. And only then can we deal with the historical changes and only then can we define a regulatory fromework based on the character, scale and intensity of MATERIAL CHANGES in those attributes.
This bullshit that makes a guy with 3,000,000 trees guilty of an offence for cutting one 2 metre sapling (that is likely to coppice anyway) must stop because it is scientifically, legally and morally bankrupt.
hardly representative of what rog?
Phil,
earlier art was essentially Romantic as was the era and hardly representative.