Over the past six years of monitoring, the Lachlan selected area has had the greatest diversity of plants recorded of all seven selected areas across the Murray-Darling Basin with a whopping 359 species recorded. This is quite an achievement considering that the Lachlan receives a small fraction of the total volumes of environmental water used in the Basin. Most of the species we record in the Lachlan are native and consist of a diverse array of plants from different growth forms and functional groups.
We made this discovery when, following a wet summer in 2021, we headed out to do our autumn vegetation monitoring, happy to be back out in the field along the Lachlan River. Even after heavy rainfall and flooding earlier in the year, we found by mid-May many of our sites were dry. With these dry conditions in mind, we were surprised to find a range of native vegetation that normally only survives if flooding conditions still persisted.
Autumn vegetation monitoring during 2021 highlighted how it doesn’t take long in the lower Lachlan for conditions to dry off. The drier than average conditions experienced in April and May leading up to our surveys in mid-May, contrasted with the wet conditions experienced in most of 2020. Many of our plots had very low groundcover, with few annuals and primarily perennial saltbush species, which are accustomed to the drier conditions. This was in stark contrast to our spring surveys where the same plots supported much higher groundcover.
Despite some sites being dry, other monitoring plots were not, and it was great to see that the translucent flows that occurred in November 2020 were still making a lasting impression on parts of the floodplain. Some wetlands such as Moon Moon Swamp and Whealbah Lagoon were still holding water, covering over our monitoring plots or transects during our surveys. Surface water had recently receded at our plots on other wetlands such as Lake Bullogal, Lake Marool and Murrumbidgal Swamp.
What is a translucent flow?
Translucent flows occur when a portion of water from specific inflow events is passed through a regulating structure – usually a dam – to enable a near-natural flow pulse into the river system. They are often used to top up natural flows so that they last longer and extend further. Floodplains on regulated rivers rarely get large enough flows to become fully covered (or inundated) – this is where a translucent flow can be used to ‘piggy back’ on natural floods and give the floodplain the drink it needs.
At wetlands that flooded as a result of the translucent flows late last year, we had a range of native aquatic and amphibious plants recorded during our autumn survey. Most of these wetlands had not been flooded since wide-scale flooding in late 2016, so for these native aquatic and amphibious plants, this water is much needed. These interesting (typically) short-lived species make up the groundcover during and following flooding, and play a range of important roles in maintaining healthy floodplain-river ecosystems. These species have adapted to the highly variable conditions (often unpredictable wetting and drying cycles) by lying dormant in the soil seed bank during dry periods. They typically germinate, grow and reproduce rapidly when the conditions are right – which is typically during and following flooding events. While the seed of these species can remain viable over multi-year droughts, flooding is vital to maintain them in the landscape by providing the conditions to replenish the soil seed bank. As such these species are more common and in a greater abundance at our more regularly flooded sites.
What is the difference between aquatic and amphibious plants?
Aquatic and amphibious plants have different adaptations, which means they survive in different conditions. Aquatic plants live solely in water throughout their lifecycle. They have to be submersed so they can grow and survive.
On the other hand, amphibious plants can live in both aquatic and terrestrial conditions. They have adapted to this by propagating through tubers or rhizomes (underground stems that sprout new shoots) and time their lifecycle with water availability. For example, the native Nardoo is an amphibious plant that lies dormant in the soil during dry conditions. When flooding or heavy rain occurs, the plant releases spores and flourishes.)
After being inspired by a book of locally written bush poetry called Back Block Bards, he bought from Booligal Pub during the field trip, Matt Jeromson who was assisting us with our fieldwork campaign decided to write a poem about our experiences at Moon Moon Swamp – including our near miss with a tiger snake! I thought I should share it, along with a watercolour Matt painted of Moon Moon Swamp.
Tigers at Moon Moon
The wetland was full, at that place called Moon Moon,
when we arrived with our truck and our notes.
To proper measure there, would have been a ghastly fare
but at least we saw a couple of goats.
We stopped and we looked, and we scrawled on a page
when we decided the Azolla would do.
But while wandering about, Becs screamed “A snake is out!”
and Alica jumped out of her shoes.
