| A
Volunteer Community Awareness
Program
for Louisa Creek |
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PLANT COMMUNITIES OF
LOUISA CREEK
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Prior to settlement Louisa Creek would have flowed through a variety of
habitats such as riparian forest, open and melaleuca woodland to coastal
wetland communities. Today a significant portion of the catchment has been
urbanised with land use now ranging from residential through to industrial
and special purposes. The urbanisation has resulted in the vegetation communities
becoming fragmented and degraded through the growth of weed species. However,
despite these pressures the creek retains very high environmental values
including:
- Remnant vegetation habitat for diversity of birdlife, small mammals
and reptiles.
- High fish habitat values due to its connection with Town Common,
Bohle River and Great Barrier Reef Marine Park.
- Buffer between industry and housing
The two most important vegetation communities for the health of the creek
are its riparian and instream communities. Riparian vegetation is the
vegetation that grows along the creek banks such as;
- Melaleuca leucadendron (Weeping Paperbark)
- Millettia pinnata (Indian Beech)
- Eucalyptus tereticornis (Blue Gum)
- Corymbia tessellaris (Moreton Bay Ash)
- Glochidion disparipes (Cheese Tree)
Riparian vegetation has some very important functions in the health of
Louisa Creek including:
- Bank Stabilisation and Water Quality Protection: The roots
of riparian trees and shrubs help hold stream banks in place, preventing
erosion. Furthermore, riparian vegetation also traps sediment and pollutants
improving water quality.
- Fish Habitat: Both large and small snags create fish habitat
by providing cover and forming pools and riffles in the stream. Riffles
are shallow gravelly sections of the stream where water runs faster.
Many of the aquatic insects live in these riffles.
- Wildlife Habitat: Riparian vegetation provides food, nesting
and hiding places for many animals. These areas also provide valuable
wildlife corridors particularly in urban areas. These corridors allow
animals to move from one area of woodland to another.
- Thermal Cover: Riparian vegetation shields streams and rivers
from summer temperature extremes that may be very stressful, or even
fatal, to fish and other aquatic life. The cover of leaves and branches
brings welcome shade, ensuring that the stream temperature remains cool
in summer and moderate in winter. Cooler, shaded streams have less algae
and are able to hold more dissolved oxygen, which fish need to breathe.
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Instream aquatic plants are also a very important element of a healthy
waterway. Instream plants found in Louisa Creek include:
- Hydrilla verticillate (Hydrilla, Water Thyme)
- Nymphaea gigantea (Giant Waterlily)
- Persicaria attenuata (Water Pepper)
- Potamogeton javanicus (Pondweed)
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| Hydrilla
verticillate found in Louisa Creek |
Native instream vegetation is very important to the health of the creek
ecosystem. Plants, being producers, form the basis for most food webs
that are functional in the creek. Instream aquatic plants play many important
roles in the creek, including:
- Oxygen production – through the process of photosynthesis,
aquatic plants consume CO2 and produce O2 making this available in the
water columns for aquatic animals to breath.
- Providing food for foragers.
- Providing habitat for aquatic animals.
Healthy streams support a variety of instream plants and animals.
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Introduced Plants:
Many of our streams in the coastal dry tropics are impacted by the introduction
of invasive environmental weeds. These weeds have been introduced through
many pathways including: use as a cattle fodder, ornamental garden plants
and by accident. The weeds found along Louisa Creek can be put into two
groups, riparian or terrestrial weeds and aquatic or floating macrophytes.
The terrestrial weeds include plants such as: Rubber Vine, Siratro vine,
Chinee Apple, Leucaena and Guinea Grass.
The main impact of the terrestrial weeds upon the riparian zone is the
loss of biodiversity they cause. This is caused in several different ways
including,
- Competition: most weed species grow very rapidly, produce lots of
seed and several species can smother native vegetation. Weed species
are able to out compete native plants for available resources and space.
- Changed environmental conditions: some species change the conditions
in the riparian zone so native plants struggle to survive. A good example
is fire, guinea grass produces a fire that is much hotter and with a
much higher flame height. This type of fire kills native trees and allows
more weeds to become established.
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| Guinea
grass can have major impacts on native vegetation communities |
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The proliferation of aquatic weeds, particularly floating macrophytes
also has a negative effect on creek health. The two most detrimental weeds
present are: Para Grass and Salvinia. These weeds affect the creek in many
ways including.
- Blocking sunlight from entering the water column, therefore preventing
primary production in native aquatic plants reducing dissolved oxygen.
- Smothering native vegetation.
- Altering flow conditions in the creek by, physical blockage, trapping
sediment.
- Reducing habitat for native aquatic animals.
These two weeds are very difficult to control, the best way being the
establishment of closed canopy riparian vegetation.
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Para grass can significantly affect in-stream values |
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