What makes a good remnant? - What Makes a Good Farm for Wildlife? - page 24

Box 2.2. A sweet end to weeds

Exotic annual plants thrive under higher levels of soil nitrogen than typically occurred
in temperate woodlands prior to European settlement. In a novel experiment, 17
applications of carbohydrate in the form of sugar were used to reduce soil nitrate.
The sugar increased activity among soil micro-organisms that use nitrogen. This
created more favourable conditions for native perennial grasses to compete with
exotic annuals. Sites treated with sugar and seeded with Kangaroo Grass were suc-
cessfully revegetated with a sward of perennial native grasses.

The understorey layer
An understorey is typically defined as the vegetation layer between the ground
layer (up to approximately one metre) and the overstorey. Some woodland
vegetation types support only a sparse understorey. 3 Nevertheless, the understorey
is important in many kinds of woodland remnants and it can add a vegetation
layer that influences the occurrence of species like the Diamond Firetail (see Table
2.2). 4 Key components of the understorey include shrubs, wattles and regenerating
eucalypts (regrowth).

Threats to the understorey layer and their management
The understorey layer is absent from many remnant patches of woodland where it
once would have naturally occurred. Grazing by domestic livestock and rabbits as
well as competition from exotic plants are the principal reasons for this decline.
Reducing grazing pressure from stock and feral herbivores like rabbits is one way to
facilitate the development of the understorey layer, and can allow natural regenera-
tion of overstorey trees to produce the important early growth stage of woodland
(see Box 2.5). Reducing grazing pressure can be achieved by fencing remnants or by
employing strategic grazing regimes like rotational grazing or cell grazing. 20, 26, 27

Table 2.2. Species for which different components of understorey layer have been shown to be important.

Attribute Example of responding species

Amount of understorey cover Eastern Yellow Robin, White-browed Scrubwren,

Red-browed Finch 4, 5

Number of medium-sized stems Eastern Yellow Robin 4

Rufous Whistler, Brown Treecreeper 4

Number of dead shrubs

Presence of regrowth trees in the
understorey

Ragged Snake-eyed Skink, Marbled Gecko, Eastern Yellow
Robin, Jacky Winter, Black-chinned Honeyeater, Brown
Thornbill 4, 5, 7

Number of vegetation layers Diamond Firetail 4

Presence of some Acacia species Squirrel Glider 25