Mesquite Weediness Elsewhere

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Mesquite has been spread around the world as a beneficial plant since at least the early 1800's. Since then there have been many large-scale, co-ordinated introductions into many arid regions of the world, as well as innumerable ad hoc ones. Although still recognised as a beneficial in many parts of the world, at least by poorer, typically subsistence, communities, its weedy potential is increasingly becoming recognised.

Impacts have rarely been quantified. However some examples include:

• reduction of carrying capacity of pastures infested by shrubs (mostly mesquite) in New Mexico by 75 % over a 35 year period (Paulsen and Ares 1961)

• grass production in arid regions of the United States consistently reduced by 50-90 % (DeLoach 1985)

• direct costs of $US200-500 million annually in the USA, with losses to total economic activity approximately three times that amount (DeLoach 1985)

• reduction of mean annual runoff in South Africa by approximately 481 million m3 (Impson et al. 1999)

There is typically a substantial lag period, typically decades, between the introduction of mesquite and it developing into dense and intractable problems. Population explosions typically result from one or more exceptionally wet years, and probably result from both increased recruitment and the spread of pods and seeds by floodwaters. This has been repeatedly, both in Australia and in countries such as Ethiopia. There is currently no cost-effective way to manage infestations once they become extensive, either in the developing or developed world.

Large mesquite plantings have been conducted in many parts of the world since the 1970s'. It is not unreasonable to expect that many of these plantings will also result in large, intractable problems. Strategies urgently need to be developed and implemented to minimise the chances of these occurring. These will require a good ecological underpinning.

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