Thanks, Specul8. (I have an urge to call you Specky. That way I can chat with Specky and Sparky on this thread.. which has a nice friendly feel).We have to remember there are large areas in Australia that are fertile. A whole swath in NSW, where a huge amount of our produce comes from ( there is abattle on as they want to use this land for CSG - crazy .
Another example is the Dorrigo plateau in coastal central east coast. It probably had mega fauna and was burnt but it has high fertility for other reasons very specific to that area ( ancient basalt lave flows on surface, the plateau slopes back away from the escarpment ( unusual ) , high rainfall due to it being a far easterly extension of the 'Great Divide' (coast from inland , basically), so... high rain fall, low run off and erosion, basalt underlay + lotza years = 'krasnozem'
Which may look like , inland 'soil' but it isnt .
... and just down the hill near my place
Not dry or desolate at all!
Now, inland , and in other areas where those factors are different the soil is very infertile as its so old, worn out, leached, etc .
For the extreme. if one goes to the craton areas ... Pilbara, Yilgarn, etc . much more so .
This I think is the main reason a lot of Australia has such poor soils . Of course, continual fire, natural or spread by humans will have an effect , yet we have to realize, one of the main uses of fire stick was just not for 'farming' but to stop bigger more destructive burns gaining moment . So, without the fire stick management, the impact of natural fire may have been worse .
regarding animal manures, I remember from BD once we did a table of all different manures fertility , eg, chicken is high, cow, horse, sheep, is lesser but good, kangaroo is very poor. So unless we could access the quality off mega fauna poo-poo ..... ?
But I think the things I mentioned first , which basically boils down to geology and geography, would far outweigh the loss or gain from long term mega fauna - or not .
I guess the other thing to do is look at why the other areas ( like Great Planes in USA for eg) are fertile and how those soils were formed ... something I have little knowledge of .
I have a general point to make. Soils might be more stable in some areas than others, but if land is burnt often enough and long enough, and the manures being deposited (by kangaroos, as you mention) are ‘poor’, then soils will eventually erode away without much root growth to hold them. Where is your deep Permaculture and biodynamic and soil ecological understandings gone, son!? Just kidding.
But I do think stable soils are to do with deep roots. Whether trees or grasses, very broadly speaking, it’s the roots that matter, and deep ones.
Unless the burning is done right, eventually you degrade soils. I say this because deep soils produce regular and lush growth, even in dry seasons, and the plant species change through their cycles, but burns create green pick, the fast food of landscape (IMO). Green pick, all of sudden, makes me wonder if we are talking about monocultures?
If Aboriginal management of landscape created monocultures, whether green pick or swathes of semi-wild cereals, then disaster was coming, surely? It might have taken thousands of years, but it was coming. Modern monoculture farming destroys soils far quicker, but the Aboriginals took a softer approach and degraded soils more slowly?
The loss of megafauna could have played a part too, for whatever reason the megafauna disappeared, whether man-aided or cataclysm made.
I am thinking things aloud, not proclaiming an agenda, btw.
Did you perchance see my posts mentioning Elaine Ingram? I am keen to know if you are aware of her? And if not, if you are interested to watch one of her lectures on soils on YouTube? I have had an interest in soils (as a pure amateur) for a long time, but having watched some of her talks, I was amazed at her thoughts and investigations. She is not alone, but I was left with so much to think about after seeing one of her lectures. Just a thought. Her ideas inform much of what I am saying and much of my thinking about Australian ‘soils’. (Her lectures are specifically on soils as a living eco-system, not centred on particular landscapes).