Salt River invasive plant clearing follow up- September 2020

Six Kingdoms project managed a follow up clearing of the Salt River.  The project, coordinated by BioWise, was stimulating and impactful and the river is looking better than ever.

The area had experienced serious regrowth since our first clearing in 2018, with dense populations of Black Wattle (Acacia mearnsii), Blackwood (Acacia melanoxylon) and Bugweed (Solanum mauritianum). Additionally other species including Blue Gum (Eucalyptus globulus), American Bramble (Rubus americana), Pampus grass (Cortaderia selloana) and Popcorn bush (Senna didymobotrya) had regenerated on the site as well.

Despite the invasive alien regrowth, the site was also showing plenty of signs of good recovery with large areas of indigenous vegetation returning. This included Keurboom (Virgillia oroboides), Mphepo (Helichrysum petiolare), Acalypha (Acalypha ecklonii), Broom cluster figs (Ficus sur) and more.

Clearing methodology

Our task this time around was to focus on all the regrowth that had occurred since our previous efforts. Due to the sensitivity of the area and the negative environmental affects of herbicides generally, full mechanical control of invasive species was used wherever possible. After cutting and removing the material from the river, we chipped it for firewood and garden wood chips. This increased the amount of time and labour required to do the job effectively, but the extra time investment was considered worth it for the beneficial environmental outcomes. 

Experimental thinning

People debate the best approach to invasive clearing to reduce future follow up requirements while accelerating ecosystem repair. Some studies show that thinning black wattle instead of clear felling is much more effective in forest systems. We wanted to see which method worked best in this context so performed a simple side by side experiment. We thinned an approximately 100m2 area of wattles from about 1 per 1m2 to 0.2 per 1m2. The intention here is to see if the extra shade provided by these trees reduces invasive recruitment and supports indigenous regrowth. By removing the conditions that result in germination (full sun) there is the possibility of reducing wattle growth into the future. 

It was fantastic to have the chance to do some much needed maintenance to this piece of land. With our efforts we’ve managed to further tip the balance back towards a healthy, diverse and indigenous system.

To read more about managing invasive plants, click here

For more information on the site and the previous work done there, click here

Converting invasive plant biomass into useable woodchips is a critical part of our process
Clearing branches from river systems is a tiring job, but critical for successful and high-quality invasive plant control.


Wattles in the flood plain had grown over 5 meters tall in just 18 months.
After clearing, the floodplain had significantly reduced biomass build up which will allow it to function as it nature intended


Bugweed before clearing
Bugweed after clearing


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