Interesting book I and 3/4 the way through, Collapse - How societies choose
to fail or succeed, Jared Diamond (I can recomend it). There is a chapter on
Aus that is good reading. The chapter is titled "Mining Australia" and says
essentially that for decades ockers have mined not only minerals but also
soil nutrients, timber resources, moisture/water and fishing stocks.

The bit about timber I found expecially interesting. I am aware that Aus
exports timber, we get oz hardwood in NZ for decks and the like. I presumed
that it was from a sustainable resource. According to Diamond this is not
the case. The rate of timber growth is slow for you compared to say NZ. Once
a forest is stripped of mature trees the conditions for regrowth is quite
difficult and can lead to the drying out, even desertification, of the soil.
Not sure I will buy any more Aus hardwood if that is the case.

He reckoned that much of the nutrient value of your bush is held in the
trees themselves. I have understood for a while that your soil is low in
nutrients given its age. It seems the trees store much of the nutrients and
recycle it through the growing cycle as they shed leaves or die and decay.
Once the trees are gone so is much of the nutrient. The trees could curvive
and grow as they existed in a closed cycle with the existing nutrients
recycled many many times. Once the nutrients were stripped away by forestry
there was nowt left in the soil for regrowth. If true, a really fascinating
example of closed cycles in nature and the way ignorant human activity can
destroy it.

He also described in some length the salinisation of your soils. I knew
about it however the author described in length how the salt pans came to
exist, how irrigation can cause the salt level to rise and dryland
salinisation results from leaving productive land bare for much of the year
allowing rain to wash salts through waterways or raise it to the surface.
The soluable salts then infest waterways.

This isn't a criticism mind, kiwis have done a good job of habitat
degredation as well. I guess our environment is not so fragile in many ways.
I did not realise just how fragile the Aus environment was (aside from your
droughts).

Comments welcome.
rob