تجزیه و تحلیل هزینه فایده از پاکسازی پوشش گیاهی بیگانه برای راندمان آب و گردشگری در یک حوضه آبریز کوه در کیپ غربی آفریقای جنوبی

Economic analysis is used to assess the costs and benefits of restoration following clearing of invasive alien trees in the floristically rich Fynbos mountainous area near Franschhoek, Western Cape of South Africa. The Groot Drakenstein, Franschhoek and Jonkershoek mountains receives more rainfall than the surrounding areas and is an important source of water for the city of Cape Town. The costs of alien invasive plant removal, gully-erosion repair and reseeding with indigenous plants are considered in a case–study cost–benefit analysis of restoration, in terms of the water and tourism benefits derived. Three different options of restoration (comprehensive, moderate, basic) were analysed under three different economic scenarios (optimistic, realistic, pessimistic) and the costs of which have been weighted up against the income derived from the supply of water and tourism. The results have shown that despite the high costs of restoration, the basic restoration option costs were out-weighed by the water and tourism benefits derived. This was also true of the moderate restoration option, when evaluated under the optimistic scenario and using an 8% discount rate, or a 3% discount rate under any scenario. However, this was not the case in the moderate restoration option when using an 8% discount rate in conjunction with the realistic and pessimistic scenarios. Neither was it the case when using a 12% discount rate, irrespective of the scenario. Under no scenario was the cost of a comprehensive restoration option outweighed by the benefits quantified, irrespective of the discount rate used. It was concluded that further restoration, in addition to the mere clearing of alien invasive plants, would be economically viable under certain assumptions and conditions.

When commercial plantations of Pinus species have dominated the natural plant community for lengthy periods exceeding seed longevity of indigenous plant species, clearing of the alien vegetation alone is insufficient to achieve natural vegetation recovery. The transformed area fails to revegetate and erosion problems, as well as further invasions, are experienced ( Richardson and Van Wilgen, 2004 and Galatowitsch and Richardson, 2005). Following clearfelling after 35 years under plantation, a reduction and even permanent loss or elimination of 58% of indigenous plant species can be expected ( Richardson and van Wilgen, 1986). Further restoration is therefore required to reinstate the natural vegetation structure and baseline ecosystem functioning. This study addresses the question of whether the water and assumed tourism benefits derived from restored Fynbos can justify the costs of reseeding and erosion control in addition to plantation removal and alien vegetation clearing. An economic analysis has been generated by performing a cost–benefit analysis of restoration of the Assegaaibos mountain catchment, which includes alien invasive plant removal, gully-erosion control and reseeding, in terms of the water and tourism benefits derived.

Reintroduction of as many species as possible within each functional guild is desirable because it is more likely to promote long-term resilience of the ecosystem to disturbance but may not be economically feasible. Further restoration involving some reseeding, in addition to clearing of alien invasive plants, would be economically viable under certain scenarios. If the objective of restoration is to place an ecosystem previously planted to alien trees on the desired trajectory to an ecosystem resembling natural Fynbos, partial reseeding achieved this, then no further assistance to ensure the future health and integrity of the ecosystem should be needed. The comprehensive restoration option is therefore not necessary, if the moderate restoration option achieves this goal. Cost–benefit analysis should be used as a decision aid only: it cannot offer a final verdict. As Rees et al. (2007) stated, restoration and conservation decisions have to be based on more than just monetary value. A balance between social, ecological and economic goals and objectives must be found if an ecological restoration project is to succeed. The broad range of goals should be acknowledged, as should the technical challenges facing cost–benefit analysis of restoration projects.