Case Study: Mesquite

Mesquite, Prosopis juliflora, was introduced to Pakistan in 1878 in attempts to develop forests in the desert. Mesquite has the highest BTU output of all fuel woods and it quickly became a popular source of fuel while its beans were used for animal fodder. The tree is adept, however, at invading a variety of habitats, greatly reducing biodiversity. It releases phytotoxins, which help mesquite to outcompete indigenous plants. In addition, mesquite trees are able to survive severe droughts and produce a massive number of seeds, which are viable for up to ten years. The use of these seeds for animal fodder increased the spread of this invader and the native Acacia nilotica has been widely replaced by mesquite in the riverine forests of Sindh.

Mesquite was also introduced to South Africa for plantation use, where it has caused a myriad of environmental problems. Mesquite now covers 1.8 million hectares of the Northern Cape and Northwest Province, where it has invaded water catchment areas and fynbos. As these trees replace grassland, they negatively impact biodiversity, ecosystem functioning, and catchment hydrology. A stand of invading trees uses approximately the same amount of water as a grassland in the same area during the rainy season, but during the dry season, when grasslands become dormant, the trees continue to require water. It is estimated that one tree uses 40-50 liters of water per day. Extended root systems allow mesquite to tap deeper into underlying water tables, causing the water tables to recede and diminishing the possibility for replenishment during the next rainy season. Receding water tables have led to the drying up of streams, reducing the ability of existing water supply schemes to deliver sufficient water to meet human needs.

Control of mesquite often requires physical removal. The most successful of these removal projects is South Africa’s Working for Water program. Removal of a dense stand of invading trees in Mpumalanga Province resulted in a 120 percent increase in streamflow within a short period after clearing. Successful recovery such as this provides hope for the area, but invasion continues at a much faster pace than removal.

-- Khatoon, S., "Pakistan’s Alien Forests," IUCN World Conservation, April 1997. p. 15

-- CSIR Division of Water, Environment and Forestry Technology, The Environmental Impacts of Invading Alien Plants in South Africa (Pretoria, SA: Department of Water Affairs and Forestry). p. 4-9

Related Links:
-- http://www.spmesquite.com/spmesquite/social.htmlx
-- http://www.dwaf.pwv.gov.za/Projects/WFW/Species/default.htm