What are the problems caused by wattle
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: