Mt Rogers Landcare Group volunteers have assessed the
cross-country tracks and paths again recently. Most of them have some degree of
erosion and evidence of successful mitigation work by Phil over several years.
Eleven of us began to apply repair strategies, based on Dr
David Tongway’s work, on the steepest track down the east side from the Trig
point on Sunday 23rd February. We’ve used branches from invasive
species to begin the creation of Branch Erosion Traps on either side of the
track; see below*.
On our Monday 2nd March working bee we added
‘leaky weirs’ made of loose rocks. These had the effect of slowing the rainfall
from a storm later that week.
Please reduce use of
this track to allow it to self-repair.
Please take the
challenge of creating a zig-zagging track across the grass and gradually up to
the trig point. Or choose another route
up to the top.
Rainwater moving rapidly down these tracks can significantly
affect the state of the circulating gravel path used by hundreds of Mt Rogers’
visitors each week.
Phil has spent hundreds of volunteer hours creating runoffs
from each of the tracks deflecting the water from rushing down slopes to flow
more slowly across the reserve. This process saves TCCS, the Land managers,
thousands of dollars because they don’t need to repeatedly come to Mt Rogers to
repair the main gravel path after each rainfall event.
The tracks and paths that go cross-country through Mt Rogers
change routes over the years. Kangaroos and people have their own reasons for
creating new ‘desire lines’.
Some background:
Mt Rogers was grazed since
settlement in the late 1800’s. Early residents of Flynn (1971), Melba (1971),
Spence (1972) and Fraser (1974) might have seen Mt Rogers as a paddock full of
introduced grasses and weeds surrounding about 75 magnificent eucalypts aged
more than 250 years old.
Before the grazing native
wildflowers and shrubs, supremely adapted to the thin, rocky soils, flourished
and supported wildlife and Indigenous peoples.
Kangaroos, as grazing animals,
move across their habitat from one
patch of preferred grasses to another or from one resting or sheltering place
to the next across the landscape. The minimal-impact tracks of their soft paws
went across country, rarely up and down.
Nowadays people usually prefer
straight up and down routes or tracks that let them achieve their challenges as
quickly as possible. These straight paths and tracks and the concrete drains
installed through Canberra’s suburbs move rainwater quickly away from the land
and plants it once hydrated.
Tracks’ physical states have
changed. The tracks we have used frequently look like miniature gullies or we may walk on
bare, compacted earth.
Rainwater:
Over time peoples’ feet, dogs’
paws, bikes’ tyres wear away plants, soil, rock particles and gravel on paths
and tracks.
Even Meat Ants create and erode trails from one nest hub to
another as they complete trillions of journeys between satellite colonies.
Rainwater erodes soil particles
and plant detritus from pummelled earth or soil that’s losing its vegetation.
In dry conditions wind blows the soil surface away from tracks.
Rainwater drains from Mt Rogers’
ridge to Ginninderra Creek, over the 40m Ginninderra Falls at Parkwood and
eventually to the Murrumbidgee River.
Dispersing rain drops:
When raindrops fall onto plants’ leaves, blades and fronds
they are channelled along stems and trunks towards the soil surface. On the
ground leaf litter, natural mulches of bark and twig pieces and soil-crust
lichens deflect raindrops sideways across both miniature and general
landscapes. The flow is slowed.
Rain water, laden with nutrients
from organisms’ natural decay and rocks’ minerals, moves across the soil
surface seeping into hollows and holes created from dead roots and by the
tunnelling and digging of trillions of animals; mini-beast invertebrates to the
more visible reptiles, birds and mammals.
The Bettongs reintroduced into
the fenced Mulligans Flat Reserve have begun the process of restoring the
composition of soils through their digging.
Karl Vernes, an associate professor with
Australia’s University of New England, calls bettongs ecological engineers,
digging more than 100 teacup-shaped holes in their nightly pursuit of truffles
that catch rainwater otherwise lost
as runoff.
Scores
of other small native mammals had similar burrowing habits throughout the landscape. Farming practices,
using land for dwellings, the impacts of feral animals and destruction of
natural habitats has accounted for the loss of these species and the
destruction of soils in much of Australia.
From David Tongway’s work:
*BRANCH EROSION TRAPS
Branch erosion traps (or brush piles) are structures that mimic the functioning of naturally occurring fallen branches. Typically, they are comprised of branches, twigs and leaves. They function to arrest overland flow at ground level and create turbulence in the wind at up to a height of about half a metre to capture particles being blown around. The brush piles are not intended to prevent all water movement, but to reduce the flow and intensity of water moving through. Experimental brush piles designed to have maximum effect resulted in an accumulation of soil particles, trapping of plant litter, leading to improved nutrient cycling and provision of material for soil fauna to work over, resulting in carbon sequestration and improved soil properties, by decreasing bulk density and increasing soil porosity of the subsurface soil (Tongway and Ludwig 1996). When properly constructed, they also prevent grazing of grass plants right down to the ground, by larger animals such as sheep, cattle and kangaroos*.
Branch erosion traps (or brush piles) are structures that mimic the functioning of naturally occurring fallen branches. Typically, they are comprised of branches, twigs and leaves. They function to arrest overland flow at ground level and create turbulence in the wind at up to a height of about half a metre to capture particles being blown around. The brush piles are not intended to prevent all water movement, but to reduce the flow and intensity of water moving through. Experimental brush piles designed to have maximum effect resulted in an accumulation of soil particles, trapping of plant litter, leading to improved nutrient cycling and provision of material for soil fauna to work over, resulting in carbon sequestration and improved soil properties, by decreasing bulk density and increasing soil porosity of the subsurface soil (Tongway and Ludwig 1996). When properly constructed, they also prevent grazing of grass plants right down to the ground, by larger animals such as sheep, cattle and kangaroos*.
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