The role of resource economics in the control The role of resource economics in the control of invasive alien plants in South Africaof invasive alien plants in South Africa

Author: Jane TurpieAuthor: Jane Turpie

Turpie, J. (2004).The role of resource economics in the controlof invasive alien plants in South Africa. S. Afr. Sci. 100, 87-93.

8750 introduced species. Over 200 considered to be seriously invasive. By 1997, 180 woody plant species covered 10 million

hectares of land.

General:General:

The Fynbos biome is hardest hit. Grassland and Savanna biomes worst hit in the moister

areas. Semi-arid Nama and Succulent Karoo biomes invaded

by saltbushes, cacti, and mesquite trees. Extent of invasions in forests is unknown.

The biomes effected:The biomes effected:

Realisation of implications of invasive species for water supply.

Placed it into an economic context. This led to the establishment of the WfW. Have cleared over 171 000 ha. Follow up weeding of 183 000 ha. 24 000 people employed in 2000. Spent over R3 billion.

Why established and successes:Why established and successes:

In a strict sense the term biodiversity should include ecosystem functioning as well as species richness.

Ecological-economics recognises the important role played by ecosystems in the economy.

Ecosystems have both tangible and non-consumptive values.

Tangible goods carry the most political weight.

Ecological-economics:Ecological-economics:

Structural diversity and organisation of ecosystems must be maintained.

This maintains the systems primary productivity, which in turn adds to its direct consumptive value.

Direct-consumptive values:Direct-consumptive values:

Include things like water purification and regulation as well as carbon sequestration.

Genetic diversity and organisation also maintains ecosystems economic worth in terms of recreational value, option value, and existence value.

Non-consumptive values:Non-consumptive values:

Initial studies focused on the economic consequences of water loss.

The scope then expanded to include losses incurred in tourism, natural resource harvest, pollination services, option value, and existence value.

Recently studied have also included the effect of invasions on fires.

Focus of studies:Focus of studies:

It is very costly. Would cost about R650 million per year for the next 20

years. Not enough is being spent on it which simply amplifies

the problem over time. In some areas the cost of clearing is easy to justify. Natural resources do not always have a high economic

worth. Also varies with control method. Some alien invasives carry an economic worth.

Monetary costs of clearings:Monetary costs of clearings:

The total cost of alien invasives has not been calculated due to differences in approaches used.

Virtually all the studies have targeted riparian or terrestrial invaders.

Studies have also varied in terms of the types of impacts assessed.

Secondary effects of alien invaders have not been analysed.

What about changing demands?

Short-comings of previous studies:Short-comings of previous studies:

Two methods used to value water losses, replacement costs and opportunity costs.

Alien invasions can actually lead to the breakdown of the entire ecosystem.

Two methods:Two methods:

The easiest to estimate are impacts on direct consumptive values.

Recreational value of biodiversity usually measured using the travel-cost method.

No studies have looked at effects of alien vegetation on biodiversity as a whole.

The effects of fire have been well researched. The deleterious effects of fire are increased with

invasions. Fynbos is also important for commercial fruit orchards as

well as the local honey industry.

Effects other than on water loss:Effects other than on water loss:

The other options available are regulatory and incentive methods.

Regulatory methods have been shown to be ineffective as well as not socially optimal.

Incentives will therefore be the best.

Two available options:Two available options: