It has been objective of the MCCG to restore the flora in the Moggill Creek Catchment to pre-settlement conditions.

In accordance with this,  the MCCG has a policy of planting seedlings raised from seed collected in the catchment area. These seedlings are considered to be the local forms of species that are best adapted to the area and are species which would have been prevalent around pre-settlement. 

Bryan Hacker has advised that the Nursery does sometimes use seed from outside the catchment when collecting local seed is impracticable. Often, species that were previously in the catchment are now in very small numbers or have been lost.

One of the side effects of climate change is that the zones expected to be suitable for various local species are expected to move South as the temperature warms. For birds and animals this should not be difficult as they can walk or fly South, but with plants it is a different matter. 

Climate change has happened in the past and plants have been able to adapt. Although some species were probably lost, most were able to gradually move to more suitable climes. But this time it is expected that the climate will change much more quickly and the Intergovernmental Panel on Climate Change (IPCC) estimated that only 75% of species could make the move. This means a huge number of extinctions. 

There is a varying amount of genetic diversity among individual species. Diversity is beneficial: greater diversity means increased ability to adapt to changing conditions.

Perhaps our policy of only propagating local forms when available should be reconsidered in light of present theories about climate change.

Should we consider bringing in seed from plants of species that we have locally from more Northern areas in order to gain diversity?  Could this help our local plants adapt as the climate gets warmer?

A case in point is the Grey Gum (Eucalyptus punctata). The Brisbane region is located near the Northern boundary of where the Grey Gum grows. There are odd locations of this species up to about Bundaberg and inland to Monto, and an isolated population occurs in the Barakula Forest. This magnificent tree is very selective in where it grows and seed from more Northerly areas may be a trigger to bring in the additional genetic diversity that will allow us to keep this important Koala tree thriving in the catchment as the climate warms.

Trunk of a Grey Gum, (Eucalyptus punctata) at Adavale St, Brookfield, showing scratches from koalas.   This is one of the koalas’ favourite food trees in the catchment.

 

A dilemna for us all to ponder:

If we are messing with climate shouldn’t we give nature a helping hand to make up for the damage we are doing?

Or would we just once again be interfering with nature and should we simply accept the extinctions we may be causing?

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In the upper reaches of Moggill Creek and most of Gold Creek there are very few “Water Weeds”,  but the same is not true of the lower reaches of Moggill Creek.

Water weeds need two things to prosper – light and nutrients.

In the upper reaches the creeks are mostly covered by vegetation. Some are native trees and there are some areas with a fair number of exotics such as Privet, Camphor Laurel and Chinese Elms, but they all contribute to the shade over the creek.

An open area along Moggill Creek at Tuckett’s Farm with several different water weeds. It looks like there is also some algae in the water. Actually the path alongside the creek in this estate is well treed with very few water weeds except near the bridge where it is open.

 

The fertility of our creeks increases as they descend through areas of open paddocks and past houses and then by large establishments such as the Brookfield Retirement Village. The run-off from paddocks with livestock,from roads, and from seepage from septic systems results in increased phosphates and nitrates in the creek water.

By the time it gets past the junction of Gold Creek and Moggill Creek the water has picked up substantial levels of nutrients and in times of low water flow can be quite turbid.

Added to this, the clearing of the banks of the creek in some areas along the lower Moggill Creek has in effect supplied all the nutrients and light required for the growth of water weeds.

These nutrients have to go somewhere! They are either flushed out into the Brisbane River in strong creek flows, result in dense algae growth or they promote the growth of water weeds.

This photo is of two large water holes that were part of the Dart Farm. They were regularly used for many years up to about the 2nd World War.  They are about 8m wide, 500m long and up to 3m deep in places, and extend from the end of Adavale St nearly to Jones Rd. The vegetation on the Northern side was removed when it was the district swimming hole. It has since regrown but mainly with Chinese Elm (Celtus) although there are some good size Sandpaper Figs and some other natives. The other side has always had a good variety of natives and a few exotics.  There is now a full canopy and virtually no water weeds.

The choices of how to handle this depends on what amenity is desired. 

It is very difficult to stop these nutrients entering the creeks. We cannot expect all the residents to return their paddocks back to native bush, nor can we close down the retirement village.

We could allow the water weeds to do their job of using up the nutrients or plant more efficient water plants along the creek in artificial wetlands to strip out the nutrients. This would would be better than algae blooms that contribute to the turbidity or worse, mats of stringy algae.

The other alternative is to replant the edges of the creek to reduce the light levels so the water plants won’t grow. This approach would rely on the creek flooding to flush out the fertile nutrient-rich water into the Brisbane River. Unfortunately this only works in big floods and small creek flows actually increase the fertility by washing the nutrients from the paddocks into the creeks.

In the meantime we probably have to accept that most of the “Water Weeds” we have in the creeks are probably doing a good job for us in reducing the nutrients in the creeks

We do need to be vigilant, however, as we do have some Elodea (Egeria densa) in the Moggill Creek. It is a fully submerged weed and is renowned as the weed that clogged up the Hawkesbury River in NSW. It will be washed out in really big floods, but can clog up the creeks in low flows.

Unfortunately it is not a noxious weed in Queensland and Victoria and it is often planted in fish ponds and farm dams and can be washed into the creeks during heavy rainfall periods.

There are very few native water plants that are adapted to water with substantial phosphorus levels. Those natives that are capable of handling the high nutrient levels can often grow so rampantly that they become weeds themselves. Bullrushes and Hydrilla are examples.

Some natives that will assist a little are Twig Rushes (Baumea spp.), Club Rushes (Bulboschoenus spp.), some Flat Sedges (Cyperus spp.), Spike Rushes (Eleocharis spp.) and Sedges Rushes (Juncus spp).

Avoid planting waterlilies, especially the yellow flowered Nymphaea mexicana (N. flava) which some years ago was a rampant weed in Gold Creek. Waterlilies have little effect in reducing the nutrient levels in the water.

Overall, however, we are very lucky in the Moggill Creek Catchment as we have some of the best vegetated and best water quality creeks in Brisbane!

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The most common large native land snail found in the Moggill Creek Catchment is the Fraser’s Banded Land snail (Sphaerospira fraseri).