Theoretical Ecology, DOI Jerde, C. L, Bampfylde, C. Chance establishment for sexual, semelparous species: Overcoming the Allee effect. Potapov, A. Allee effect and control of lake system invasion. Bulletin of Mathematical Biology. Drake, J. Stochastic models of propagule pressure and establishment. In press. Herborg, L. Predicting the North American distribution of Chinese mitten crabs Eriocheir sinensis using measures of propagule pressure and environmental niche models. In addition, no studies specific to the Agulhas Plain provide estimates of the average value of water for different industries.
This study opts to estimate the average value of water p i required to justify alien clearing and restoration at a systems level under different runoff scenarios y i equation 3. The use of average value instead of the marginal value of water is based on the assumption of constant returns to scale and price-taking by consumers. The change in annual net income from wild-flowers and other fynbos products harvested from the restored areas on the Agulhas Plain will range from R0.
Figure 4 illustrates that Proteacea flowers and cones from Mountain fynbos, and sour fig harvests from Strandveld fynbos hold the greatest potential for generating income. Total clearing and restoration costs amount to R million, of which the restoration component comprises 21 per cent. The costs incurred during the first year account for 72 per cent of total direct costs. As an indirect cost, the pollination services that Eucalyptus forests provide for beekeeping outweighs the foraging value of indigenous fynbos.
This suggests that an annual opportunity cost of R1. The additional opportunity cost of fuel wood due to the removal of Acacia Cyclops will amount to R4. Table 1 lists the range of different direct and indirect cost and benefit components. The financial net present value of clearing invasive vegetation and restoring natural capital on the Agulhas Plain ranges between -R This indicates that an investment to clear the entire Agulhas Plain of invasive species and restore natural fynbos vegetation will not be offset by the additional direct income that can be generated from harvesting fynbos flowers and other fynbos products.
When the impact on beekeeping, honey production and the opportunity cost of fuel wood is added, the economic net present value yields a negative return of between R million and R million.
The results suggest that the water released through clearing and restoration needs to be an economically valued commodity in order to ensure a cost-effective outcome. The availability and cost of alternative water sources determines whether the cost at which water can be made available through alien clearing and restoration is low enough to justify investment. Figure 5 summarises the outcome of equation 3 by illustrating the average value of water that will justify clearing and restoration under different discount rates in relation to runoff, and compares these values to existing costs of water on the Agulhas Plain.
The CAM calculates the unit cost of water water supply divided by operating costs at R5. This estimate includes personnel expenses, repair and maintenance costs and capital expenditure and is not an accurate reflection of the value of water in the area, but it does provide an average upper estimate of what the municipality is willing to pay for water supply.
At this upper estimate of water value, per cent of water released by alien clearing and restoration will have to be provided as consumable runoff in order for such a project to be efficient. Potential boreholes in the area were estimated at being able to yield an additional kl per annum Overberg District Municipality, This amounts to a cost of R2. A similar approach for water resource development in Bredasdorp provides a cost estimate of R1.
In accordance with Turpie et al. Burgers, Marais and Bekker estimate this to be R1.
Bioinvasions and Globalization synthesises our current knowledge of the Bioinvasions and Globalization – Ecology, Economics, Management, and Policy | Oxford Keywords: bioinvasions, globalization, biological invasions, zoonotic. ykoketomel.ml: Bioinvasions and Globalization: Ecology, Economics, Bioinvasions and Globalization: Ecology, Economics, Management, and Policy 1st Edition . synthesises our current knowledge of the ecology and economics of biological invasions, Paperback: pages; Publisher: Oxford University Press; 1 edition.
Our results suggest that at consumable runoff of more than per cent of water released through alien clearing, the latter will provide a lower-cost alternative for augmenting water supply. Dry land crop production accounts for a large proportion of land use on the Agulhas Plain. In South Africa the National Water Accounts are increasingly regarded as one of the more accurate estimates of the average value of water per land use type Turpie, South Africa, Assuming that dryland production practices on the Agulhas Plain are similar to the rest of the Breede WMA, at least per cent of water released through alien clearing and restoration will have to be made available for dryland crops on the Plain in order to justify the investment.
Past water scarcity on the Agulhas Plain was addressed by building dams or drilling boreholes Cape Agulhas Municipality, This study suggests that, depending on the value of water in the Agulhas Plain, alien clearing and restoration can provide a positive return if per cent of the water released is made available for consumption illustrated in Figure 5. As climate change progresses and the area becomes even more water scarce, clearing and restoration will become cost-effective at lower quantities of runoff.
Growing human societies and impending climate change is threatening the sustainable supply of ecosystem goods and services. Invasive vegetation poses an additional threat to the goods and services supplied by indigenous ecosystems. This study tests the hypothesis that alien removal and natural capital restoration may add value to invaded areas through recovering the ecosystem goods and services supplied by indigenous vegetation.
It draws from ecological, hydrological and economic observations to assess the net impact that alien removal and restoration could have in the Agulhas Plain.
The results unequivocally show that the cost of clearing the entire Agulhas Plain of invasive vegetation and restoring indigenous fynbos to invaded areas cannot be justified solely based on direct financial benefits. The results further illustrate that in the absence of water as an economically valued commodity, other indirect economic impacts are unable to justify invest- ment. Preliminary appraisals of the value of water under different runoff scenarios suggest that water at a systems level is sufficiently valued to provide an efficient outcome for clearing and restoration projects on the Agulhas Plain.
However, it is important to note that runoff and water values are industry and area specific. While the results indicate that alien clearing and restoration could be justified at a systems level, investment decisions should be preceded by an investigation into area specific runoff and water demand. Payments for ecosystem services can be used as an instrument to encourage alien clearing and restoration activities. Local municipalities on the Agulhas Plain could offer landowners payments to clear and restore their land in exchange for a proportion of the water made available.
In this way farming income can be augmented to the extent that it renders alien clearing and restoration financially feasible for landowners, while at the same time providing municipalities with a lower cost alternative of water supply. Alternatively, municipalities can decide to undertake clearing activities themselves in return for a proportion of the water made available, leaving landowners responsible to restore cleared land. Irrespective of the strategy adopted, payments must be designed in a way that ensures that landowners will continue to keep their land free of invasive alien vegetation.
Payments would have to compensate the gap between direct project costs and improved land use. With the rising economic value of water induced by climate change and growing demand, it is expected that alien clearing and restoration will increasingly become an economically viable land and ecosystems management strategy, and payments for ecosystem goods and services an efficient instrument with which such activities can be encouraged. The work forms part of the broader WRC project entitled, 'The impact of re-establishing indigenous plants and restoring the natural landscape on sustainable rural employment and land productivity through payment for environmental services'.
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