Dryandra Woodland - Department of Environment and Conservation ...

20. WEEDS
BACKGROUND
A weed is defined as a plant or species growing out of place. When growing in native bushland, an
unwanted plant is called a bushland or environmental weed.
Weeds may cause major structural change to native plant communities, altering flammability,
displacing threatened species and regenerating seedlings, dispossessing native animals of habitat or
food, and changing ecosystem processes such as the cycling of water or nutrients.
Healthy native vegetation is normally able to resist invasion of weeds. Most weeds require certain
conditions, including the opening up of the canopy, soil disturbance or influx of nutrients before
they can spread.
The major source of weeds at Dryandra is from adjacent lands. Major routes of spread are across
private property boundaries, along linear disturbance features such as roads, tracks, and railway
formations, and along creeklines. Weed dispersal can be increased by vectors including vehicles and
machinery, soil movement, and by native and domestic animals.
Of the 890 plant species recorded within the Woodland, 74 are introduced (38 monocotyledons and
36 dicotyledons). Of these, the cape tulips (Homeria flaccida and H. collina) are declared category
P3 weeds under the Agriculture and Related Resources Protection Act 1976. Category P3 plants are
those where the numbers of plants or distribution, or both, should be reduced. Soursob (Oxalis
pes-caprae) is declared P4, ie. those plants that should be prevented from spreading beyond their
present distribution.
Some areas, such as creeklines and granite outcrops, are highly susceptible to weed spread due to the
high water and nutrient status of these sites. Weed propagules can also be carried down streamlines
by water. Most of Dryandra is uplands; consequently weed spread by this route is slow. However,
upstream spread of cape tulip, Guildford grass (Romulea rosea), Cape Weed (Arctotheca calendula),
clovers (Trifolium species) and Soursob is occurring on some of the creeklines.
Grasses such as veldt grass (Ehrharta species), wild oats (Avena species) and African Love Grass
(Eragrostis curvula) can increase the fire hazard and out compete native vegetation for water and
nutrients.
Other weeds such as Bridal Creeper (Myrsiphyllum asparagoides), watsonia (Watsonia species),
Freesias (Freesia leichtlinii) and perennial grasses are not yet a problem in Dryandra; however, they
do pose a threat to native vegetation because of their ability to invade and then dominate native plant
communities.
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