birding-aus

Erosion, land-clearing & grazing

To: "b-a" <>
Subject: Erosion, land-clearing & grazing
From: "Syd Curtis" <>
Date: Sun, 27 Aug 2000 06:43:24 +1000
I've read with much interest  messages concerning the probability of 
land-clearing helping to control erosion in some circumstances.  I have no
personal experience of the country under discussion, but I wish to report on
a situation with which I am familiar.

When I was growing up on Tamborine Mountain (red basaltic soil; high
rainfall; 70 km south of Brisbane) my father was concerned at the
proliferation of blady-grass (Imperata cylindrica) at the expense of
Kangaroo Grass ( Themeda triandra) where he was grazing cattle, Blady-grass
being coarse and virtually inedible except for the new young shoots after
fire.  He attributed this replacement of 'roo grass by blady to the effect
of fire, a not unreasonable observation given the way that blady-grass
shoots appear so promptly after fire.

However, I am sure he was mistaken.  It was not the fire but the grazing of
cattle that was the cause.  There are areas on the side of Tamborine
Mountain that are so steep that cattle cannot graze them: all 'roo grass.
And of course those steep slopes would burn with a very hot fire every time
there was one.  Similarly one can see beside the railway line to Kyogle (in
NSW), beautiful swards of pure 'roo grass from fence to fence, despite
Railways burning off along the line each year, and outside the fences where
cattle are grazing, extensive infestation of blady-grass.

This makes sense for the 'roo grass is a soft tufted grass.  Young seedlings
would be easily uprooted by a grazing cow, and furthermore, 'roo grass is
propagated by seed, which may not be produced if the plant is eaten off by
cattle.  Blady-grass has strong rhizomes - underground runners - by which it
spreads and from which the strong shoots emerge immediately after fire.

So I wonder whether the perceived increased erosion where shrub/tree growth
replaces grassland, is also due to grazing of domestic stock, rather than
the change in vegetation.  It would be interesting to have a report of the
situation in an ungrazed area - if any exist.

May not the Mitchell Grass plains be an artefact of Aboriginal fire-stick
farming?  And that without regular burning, there would be a natural
progression to a very different climax ecosystem?

Syd Curtis


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