[Pil-pc-oceania] About Keith Stewart's experience-- 17 March about rocks

[Rosemary Morrow]

Rocks and stones....(First published in Blue Mountains PC email  
newsletter)

I try to understand the ecological functions of everything in the  
environment and so when I was recently working in my garden which is  
underlain with gravel and stones I tried to make the connextions and  
here is a precis of what I think is happening.

A short meditation on rocks and stones in ecosystems.


I’ve spent quite a bit of time lately digging around in my soil which  
I love.  ( I was a wombat in my last life.)  However,  through  
sifting through the soil I became interested in the stones and rocks  
and how they function.

Stones, rocks and water
Our beautiful natural creeks and streams are full of rocks and an  
archtypal photo is one of clear water running over stones with  
overhanging ferns or ti-tree. These stones, like everything else in  
our ecosystem webs function for the good of the whole. They are a  
defence against the pounding of water in floods which so easily  
erodes the banks.   The rocks accept the force of the water and save  
the plants and soils on the edges.

Their rounded shapes enable the water to move in its natural  
spirals.  Their naturally graded sizes enable some of the rock to  
move if the force of the water is very great.

In the riffles, the narrowing of the creek bed, they help to  
oxygenate the water as it rushes over them.   Then the creek widens  
out again into ponds where some of the water’s load can settle and we  
get one of those lovely bush ponds with stillness and reflexions.

In rehabilitation of creeks and streams, stones and rocks will be an  
essential resource.

No wonder bushrock is classified a “non-renewable” resource.

Stones, rocks and soil
It’s not so obvious how rock is so valuable in soils.  I have made  
some observations and from these, some deductions quite possibly  
wrong but worth thinking about.  Soil stones are often flat or  
angular and so would hold or redirect water on a micro scale.

It also seems that the surface interface of stone and soil is a  
special ecotone and perhaps an ignored one.

The surface of stones is often damp and any sticky soil clays adhere  
to their surface and I think there is an exchange of clay minerals  
here where the rock surface is undergoing a very slow change to a  
more permeable state.   It’s as if the soil is slowly removing the  
skin of the stone.

The processes of condensation and evaporation from the stoney soils  
seem more active than from stoneless soils.  They are active perhaps  
because of the larger mass of stone and probably its composition.    
These soils are damper and warmer.   It is noticeable that the stones  
in the soil are quite warm within about 30 cm of the soil surface.   
They don’t seem to cool down as much at night perhaps because the  
upper soil layers act as an insulation blanket for stones.   It seems  
as if they act as a heat bank for the soil and so would enhance the  
root growth of plants.

I’ve seen people sieve and rake soils to remove all the stones  
because they feel the roots are blocked by them.   I’m inclined to  
think that stoney soils actually enhance root growth by providing an  
special micro-environment of nutrient and water.

Has anyone else thought about this?

Rowe Morrow.   2007



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