What are the problems caused by wattle
Wattle trees are more problematic than you think. They don’t only sap valuable water….
The common and simple message about wattle, is that it sucks more water out of the catchment than indigenous vegetation. If that were the only problem with wattle, we would march out there and poison the lot and walk away. Until now several agencies have done just that. Doing that is a problem! It is an issue because in doing only that, one has not solved the problem at all. The need to understand the difficulties about wattle is therefore important when planning the removal of a wattle grove, including the timeline, resources and budget you may need.
Wattle does indeed sap a lot of water. I have heard figures of 1300 to 1600mm per annum. Rainfall in the area where we work is between 800 and 1200mm per annum.
Other important effects of wattle relate to the allelopathic effect, in which the plant prevents other species from growing in its leaf zone. I explore that on a real site outdoors in this video here:
Apart from how much water they draw, consider these aspects: Andrew takes us through a grove of wattle trees and shows real examples of the harm that they can do.
Another aspect to consider, is that wattle seed remains viable (i.e. they can germinate) for a whopping 60 years after they land on the ground! Wattle seeds are also triggered to germinate by fire.
As a legume, wattle puts some nitrogen into the soil. In addition, it causes the wash away of topsoil. Take a look at this explanatory video: wattle problems explained It also acidifies the soil. If you add all these factors together, it means that a patch of felled wattle will only be suitable habitat to a particular suite of species. Those species are pioneer species, and most are alien and themselves invasive. This is very evident in the field. One cannot wish grassland back! It is really hard work, and no one has nailed the formula of what to do, when the patch becomes a jungle of blackjack, wattle saplings, khaki bos, and bug weed. It is certainly easier if you patch is on flat land, accessible by tractor, and if the area has been de-stumped. I say this because continual mowing works really well in getting grasses back in there. But in the steep and sometimes remote valleys, this is not possible.
This business of wattle removal is therefore maturing into a more holistic field of “grassland re-establishment”, of which the initial felling, and even the first year or two of follow up, are very clearly just the beginning.
From a paper by Yapi, O’Farrell, Dziba and Esler, we learn:
“ active restoration is required to enhance ecosystem recovery (Beater et al. 2008; Gaertner et al. 2011; Le Maitre et al. 2011). In some cases, elevated levels of soil nutrients (Yelenik et al. 2007; Gaertner et al. 2011; Witkowski 2012) derived from nutrient rich litter, and N fixation in the case of legumes, can lead to the undesirable situation of reinvasion by the same and or other species after clearing”
So in summary, wattle causes erosion and sucks water, and its other, and equally significant problems manifest when you cut it down.
Further reading:
Re establishing grassland
What to do after the wattle is gone…
Re establishing grassland
Its not easy!
Re-establishing grassland is not easy! After removal of wattle, one inevitably ends up with bare earth, somewhat rich in nitrogen from the legume effect of wattle, arguably still affected by Wattle’s allelopathic effect, and littered with woody debris. Going from this to dense grassland does not happen easily. In fact, it could be argued that this step is more difficult than the task of removing the trees themselves.
For one thing a fire may have gone through the landscape. This could be a natural occurrence, or a move by the landowner to “tidy up”. Burning is also not necessarily wrong. In fact one school of thought is to burn regularly, so as to trigger germination of the huge bank of wattle seed, as a means of ‘flushing it out’. There is real merit in this. But if the trash has been piled high, the fire will have been damagingly hot, and the earth will be baked and laid bare. The pulverised, baked earth is often best described as orange talcum powder. It has no structure, is hydrophobic, and nothing will grow in it. It represents a real erosion hazard!
Quite aside from burn areas, the ground is receptive to pioneer species, most of which are alien. Blackjacks (bidens pilosa), Khakhi bos, and other tall species grow. They have a poor basal cover, but are better than bare earth. The challenge is to get desirable species in before those weeds can predominate and shade out the species we would like to see. By all accounts, seeding a mix representative of highland sourveld is something that has never succeeded. Locally, a “summer veld mix” can be bought, and although it is not fully representative of the highland species mix, it comes as close as one can get. Initially we preferred a mix of Lovegrass and Teff (Eragrostis curvula and Eragrostis teff). Teff is indigenous to Ethiopia, but it is an annual and does not re-seed. Its advantage is that it germinates quickly to hold the soil, and will attract cattle, bearing other species in their dung. The curvula takes longer to germinate but does come away well in the end. The problem is that the teff does not germinate if merely scattered on the site: it must be raked in. It also will not germinate if there is a dry hot spell of weather. Also, the curvula tends to dominate and not allow the natural ingress of a diversity of species. So we use the “summer Veld Mix”, and we seem to be having success.
This quote from Grassland habitat restoration by Smith, Diaz and Winder , sums it up well:
“We conclude that there is no “quick fix” for the establishment of a grassland community; long-term monitoring provides useful information on the trajectory of community development; sowing gets you something ,but it may not be the target vegetation you want that is difficult to establish and regenerate; it is important to sow a diverse mix as subsequent recruitment opportunities are probably limited; post-establishment management should be explored further and carefully considered as part of a restoration project.”
and from Farmers Weekly:
“Effective restoration of encroached areas is not a short-term project, but a long-term commitment. “Chopping down a few trees and using a bit of poison here and there won’t solve the problem. There’s no quick-fix – you need a management plan as well as a budget if you want to succeed,” says Arnaud. “But,” he adds, “the rewards pay off as the land becomes more productive and animals can flourish.”
Our best summary of the way to do it, will follow in further posts…….