About 250 thousand acres of wattle trees are propagated for commercial purposes in the Union of South Africa, primarily for the wattle bark, or its extract, which have valuable tanning properties. The bark reaches maturity when the trees are from eight to ten years of age and the timber is used in the gold mining industry and as fuel. Two species of wattle, originally introduced from Australia where they are indigenous, are grown commercially from natural seed; green wattle, Acacia decurrens Willd., and black wattle. A. mollissima Willd. The growth of A. decurrens wattle is mostly thought of as being superior to A. mollissima under unfavourable conditions in South Africa, however, as a result of its bark containing an excessive amount of red colouring matter, the tiny proportion of A. decurrens in cultivation is slowly disappearing in favour of A. mollissima.
The environmental and financial effect caused by invasive species on native plants in Australia is not broadly reported by barely any contextual investigations, notwithstanding increasing awareness of the potential of indigenous plants as weeds. The effects of invasive alien plant can incorporate disturbance to environmental cycles by sped up biomass accumulation, decreased light infiltration, increased nitrification, changed fire intensity and frequency, altered geo-morphological processes, hybridisation with congeners, which can prompt decreases in the richness of species and diversity. A large number of these effects are like the attack of plants beginning from different nations (alien plants). Nonetheless, measured effect data on biodiversity esteems are only distributed for Pittosporum undulatum Vent. (Mullett and Simmons, 1995; Rose and Fairweather, 1997), Leptospermum laevigatum (Sol. ex Gaertn.) F. Muell. (Lam and van Etten, 2002) and Acacia longifolia (Andrews) Willd.
The environmental effects of Australian invasive plants, particularly acacias, are the most contemplated species in South Africa, it was discovered that thirteen of these plant species are currently naturalized, and eight of these plants cause far reaching alteration of biological communities and ecological systems (Richardson and van Wilgen, 2004). While a comparable size of infestation and effects are still to be revealed from indigenous acacias in Australia, indirect proof demonstrates that the potential is there. Vigorous population growth of A. longifolia, A. dealbata Link, A. pycnantha Benth. and A. decurrens Willd. in Western Australia; A. cyclops Cunn. ex Don in South Australia; and A. saligna (Labill.) W.L. Wendl., A. baileyana F. Muell. and A. longifolia in eastern Australia indicate broad-scale impacts could also be inevitable if there is no implementation of acceptable management measures
As invasive native plants are increasingly recognised as problematic in natural vegetation (Adair, 2008) many are subject to suppression programs to protect biodiversity values. Control options vary according to life-form, susceptibility, risk of non-target damage, ease of implementation, size of infestation and outcome targets. Control choices for indigenous plants incorporate the utilization of herbicides, managed fire, grazing, mechanical eradication, biological control, and coordinated strategies, including the profoundly viable technique (for some woody plants) of 'rolling' infestation with substantial equipment, then using fire after a time of drying (Muyt, 2001).
1.1.1 Occurrence of species under study
1.1.1.1 Acacia decurrens
Acacia decurrens is indigenous to plateaus of Victoria and New South Wales and temperate littoral to inland zones that are cool but not to xeric or hot regions of inland New South Wales. It occurs in high precipitation zones with 600 – 1,400 mm per year and is generally tolerant to a wide range of environments. In forests and xeric sclerophyll forests in New South Wales, it establishes with plants such as Eucalyptus punctata and small leaved Eucalyptus crebra (Benson and McDougall, 2001). In territories where it has become naturalised, Acacia decurrens is commonly found along the roads, creek lines and in wasteland areas. It also develops in disturbed locations adjacent to bushlands and open forests (Benson and McDougall, 2001). It was broadly propagated in New South Wale, and it is hard to tell whether it is indigenous or naturalised in zones close to its native rangelands.