Box 3.8 Case study of mesquite introduced into Wadi Hadramout in Yemen

Prosopis cineraria and P. juliflora were introduced to the Wadi Hadramout (2.2 M ha in Seiyun Town Park) in Yemen in the mid-sixties. In 30 years, P. juliflora (mesquite) has spread from just a few trees and now occurs extensively throughout the 2.25 M ha Wadi. P. cineraria was also planted around Seiyun in 1980 but has not spread to the same extent, and is less vigorous.

Method of spread. Mesquite was spread via ruminants which ingest seeds and excrete them in manure. Manure is a common source of fertilizer for agriculture (P. cineraria is not spread in this way as seeds appear to be digested by the animals). With a high content of hard seed, passage through the digestive system of ruminants acts to scarify mesquite seed. 

Mesquite was found to be well adapted to environments with high moisture such as drainage lines, irrigation canals, bridge inlets and outlets and irrigated farm lands. It has invaded disturbed land but has been less successful on land where native vegetation is still vigorous.

Farmers are not unanimous in condemning mesquite as it has a number of beneficial features such as:

• Use as building poles as P. juliflora seeds less susceptible to borer attack than other Prosopis species

• Honey made from mesquite is of excellent quality

• Withstands severe drought

• Provides shade and forage for livestock, particularly during the dry season

• Protects Wadi banks against erosion

• Supplies fuel for rural poor, makes excellent charcoal

• Can be used as a live hedge to control stock movements

However the disadvantages of mesquite are substantial and include:

• Blocks flow of water along water ways resulting in flooding

• Competes with palm trees eventually killing them

• Only the pods are palatable to livestock and not the leaves. This means that large quantities of pods are consumed and excreted in manure.

• Very high pod production occurs e.g. 3.34 kg per tree ensuring rapid spread, with seedlings germinating at very high densities forming thickets

• Seeds can be transported long distances by goats and sheep, and by water to favorable sites some distance away

Mesquite control: Mesquite is difficult to control. Burning is effective with young trees and management also plays a role e.g. it is important not to spread manure, which contains a lot of seeds. This is a difficult option due to the importance of the manure as fertilizer. Fermentation of the manure prior to spreading kills the seeds and mechanical uprooting can also be effective.

In conclusion, the spread of mesquite in Wadi Hadramout has been rapid and caused many negative effects. Although there have been benefits as well, it appears that these may not outweigh the negative effects.  

Source: E. A. Elsiddig, unpublished report to FAO