PIMP MY DUMP: CREATING POSSUM HOMESThe NPWS Landforms and Rehabilitation Team is tasked with
rehabilitating sites within Kosciuszko NP that were disturbed by
the Snowy Mountains Hydro-electric Scheme. After underground
blasting of tunnels and the cutting of benches for aqueduct
pipelines, large volumes of rock were dumped, resulting in a
some valleys being filled with spoil rock. Rehabilitation was
considered necessary for landscape aesthetics, to cover exposed
surfaces, to improve geotechnical stability and prevent further
alteration to waterways, and to decrease the risk of erosion
and weed invasion. Sites for rehabilitation included Happy
Jacks Valley. Happy Jacks Spoil Dump 1 is made up of material
excavated during construction of the Happy Jacks Shaft and
Eucumbene–Tumut Tunnel from 1954–59 and is estimated to
contain more than 650,000 m^3 of spoil material. The top of this
dump is some 1250 m asl, and the toe is at about 1180 m asl.
Since its construction, natural regeneration has been minimal,
with one highly unstable long slope of 45 ̊ extending from thecrest down to the river, and a highly compacted bench on top.
Before the rehabilitation process, a fauna survey of all major
disturbance sites was undertaken.
To make suitable habitat for mountain pygmy-possums,
excess spoil material from the crestal cutback of the spoil dump
slope was shaped into a mound at the top of the slope (termed
the ‘pyramid’). An artificial rock lens (simulating boulderfield
conditions) was created on the eastern side of the mound,
which meant moving 80,000 m^3 of rock spoil to stable areas
within the site and planting an area of some 65,000 m^3 at
the top of the spoil dump. The rock lens was excluded from
planting and mulching because the sawdust and compost
would infill rock interspaces, which are an important habitat
component. Seed and cutting material in planting areas
adjacent to the artificial boulderfield habitat was collected and
included primary habitat plants such as the mountain plum-pine.
A total of 62,000 tubestock seedlings were planted.The first smoky mouse
caught on the artificial spoil
dump. Photo: Martin Schulz
Seen from above, the magnitude
of the rehabilitation task becomes
clear. Photo: Martin SchulzHANGING ON
Another surprise was in store for me, too. One steaming hot day
in February 2013, as smoke billowed from a nearby bushfire, traps
on isolated natural scree slopes above the Tumut River revealed
four individuals at the lowest location found so far – just 1195 m
above sea level. Could this species persist at altitudes no one had
yet considered? Since it preferred special walnut bait, had traps
set for other small mammals, using standard peanut butter baits,
simply failed to reveal its existence?
If you build it, they will come
Back at Happy Jacks Valley, more detailed trapping was underway.
Radio-tracking of individuals confirmed a population dwelling
on two more spoil dumps, commuting to nearby natural scree
slopes. Tracking data revealed that most days, at least some
radio-tagged individuals slept deep within the rock spoil. On
occasion, up to four tagged pygmy-possums huddled in the same
shelter site. But not all spoil dumps yielded our quarry. Spoil
Dump 1 proved an enigma. Potential habitat covered its slopes,
but we found no possums there – only on the track above and
in a small area of scree up from the Tumut River, 1200 m above
sea level. The absence of the pygmy-possum from the rest of
Spoil Dump 1 encouraged rehabilitation works to restore upper
sections of the spoil dump face and the extensively cleared
crest. Compacted rock, tens of thousands of rusting nails, and
very little vegetation likely contributed to the failure to trap
any small mammals there, which led to the idea of creating
artificial boulderfield habitat during the rehabilitation process,
specifically to attract mountain pygmy-possums.
In November 2014, some six months after the creation of the
boulderfield, we were keen to trap. Result: no small mammals
at all. The following spring, there were still no mountain pygmy-
possums, although the house mouse (Mus musculus) liked the
created habitat. Individuals had been trapped less than 180 m
away, on the edge of the access track and in the south-east
corner of the spoil dump, so why not here? Little was I to know
that a huge surprise (although not if you take into account body
weight) awaited me at Trap 12 on the second day of checking.
A closed trap.
A house mouse? I thought, as I picked up the trap. Too heavy.
A snake or a blue-tongue lizard? No. Something didn’t feel right.
I peered in, my heart starting to hammer as it had that eventful
day five years earlier. A rodent, blue-grey in colouration, stared
back at me. It could only be one thing – another endangeredWildlife Australia | 21