Black wattles line the banks of many streams in the KZN and Eastern Cape highlands, on the eastern side of the escarpment. In fact when flying over the landscape, or looking at an orthophoto, you can see where the rivers run by tracing the snaking ribbons of wattle trees.
The leaves and flowers of a Black Wattle (Acacia mearnsii)
They seem to favour the moist environs, and don’t appear to be a threat in the drier montane places like the Rhodes area. They don’t do all that well in the higher Cape Mountains, but are clearly a problem in places like the lower Witte River valley
The problem with these trees in the moist areas, is that they are an invasive species, meaning that they are spreading wildly: they are in a runaway expansion mode. Conversely, an oak tree for example, while not indigenous to our country, is not spreading and/or threatening any other species or creating any sort of problem
(And it always puzzles me that some environmentalists put Trout in the same category as wattles, not as Oak trees, despite the fact that they are most definitely NOT in a runaway expansion mode in South Africa. It all seems very illogical, but let’s put that topic aside for now)
Back to wattles and their expansion. They don’t burn easily (timber farmers use them as a firebreak); their seeds germinate thickly even many years after they have fallen to the ground; they are 'allelopathic', meaning that they have a natural defense mechanism, whereby no other species will grow close to them; and partly as a result of that, they tend to create bands of wattle monoculture. They also fall over into rivers, causing an erodable foot wound, and creating log jams that render a stream unfishable. Why is that a problem? Well to quote the Global Invasive Species database:
'It threatens native habitats by competing with indigenous vegetation, replacing grass communities, reducing native biodiversity and increasing water loss from riparian zones.'
And to quote Matt Wood, editor of life sciences blog :'Insects and microbe decomposers that live in streams depend on a variety of nutritionally diverse leaves that fall into the water as a food sources.'
And, as was explained to me by our own Jake Alletson, the tannin rich leaf matter that they produce is alleged by some to be poisonous to insects, but even if you don’t agree with that, it seems to be widely accepted that their leaf matter is preserved by the tannins. It is therefore not available to microbes, and since wattle leaf matter occurs to the exclusion of any other leaf litter in zones of wattle domination, there just isnt any food there.
So under that ribbon of wattles , the biodiversity is most certainly snuffed out.
Click in images to enlarge
Wattles lining the Umgeni River
Now before the scientists take me down for incorrect quoting protocols, biased and cherry picked quotes and the like, let me just say that the above quotes support what I see on our Trout streams.
Under a tunnel of these trees, one sees Heptageniidae nymphs predominating under river stones, above all else. You see fine silt covering rocks. I attribute that to the bare ground beneath the trees, and the fact that banks no longer have dense stands of grass. You see heavily shaded water. And if you speak to old timers, they will tell you that the flow in our rivers is WAY lower than it used to be, especially in dry times, like at the end of winter.
I can tell you that my fishing logs support the assertion that Trout populations are lower on stretches of river where wattles predominate, and are better on the same stream where it flows through pastures, Ouhout and natural grasslands.
When you are off flyfishing on a lovely stream and you see a tiny little wattle sapling, do us all a favour……KILL IT! Take out your penknife, use your teeth, anything, just kill it while it is tiny please. When wattle trees get bigger, they are so hideously expensive to eradicate that few people have the mettle to even try. And when that happens: Bye bye Trout stream!
Removing full grown wattles from trout streams is very hard work!
It is one of those insidious, cancer like things. I believe that we as fly-fishermen need to start doing something about it before it becomes an obvious problem. Hence my encouragement to anglers to learn to identify black wattle, and to pull them out as you walk the Trout streams and elsewhere.
Here are some Trout streams that I know of, where wattles are in various stages of throttling the life out of everything.
The Ncibidwane, tributary of the Bushman's. Wattles high up a hidden valley, way up into the world heritage site. Not too bad at all (yet), but they are unknown, unseen, and unchecked.
The Mooi River below the Reekie Lyn stream: a sprinkling of trees, but I tried editing all the wattles out of my photos from a day’s fishing there last year, and it was a bit like my aged uncle asking the barber to cut out all the grey in his hair!
An angler framed by Wattles on the Mooi River (KZN)
Side valleys and the main Bushmans from below Chris Brown’s farm, all the way down to Rockmount and below: there are some quite bad patches there.
The Inzinga above the Lotheni road: a dense stand on a short stretch there.
The Umkomaas up at Vergelegen: a lot of small saplings. Ezimvelo has clearly done some work, but we should help them.
The Luzi as it tracks the lower Pitseng pass (quite awful!)
But in general, on the eastern seaboard of the Eastern Cape and KZN, every trout stream is affected. I don’t know any in KZN where you will not find at least some wattle saplings.
Streams where there is a problem, but something is being done about it:
The Mooi at Game Pass (Well done Ezimvelo!)
The Umgeni (Thank you WWF, NFFC and others)
The Little Mooi as it comes out of Highmoor…I think it was 'Working for Water' who felled these: a fantastic job!
Game Pass, Mooi River, KZN: the foreground in this picture was once a sea of wattles before Ezimvelo rehabilitated the area.