Current and potential distribution of Parthenium hysterophorus
Parthenium hysterophorus (Asteraceae, EPPO Alert List), originating from Central and South America, is considered one of the world most serious invasive alien plants, and is already highly invasive in Australia, Asia and Africa. A climatic projection was performed for this species with the software CLIMEX to consider which areas are at risk. The species grows on a wide range of soils ranging from sandy to heavy clays, and occurs in areas with summer rainfall greater than 500 mm per year. Germination can occur at temperatures between 10°C and 25°C.
The species may enter new territories through its seeds contaminating earth moving and harvesting machinery, animal stock, fodder and grain. P. hysterophorus can establish in disturbed habitats such as railways and roadsides, wastelands, fallow lands as well as grasslands, river banks and floodplains. Its numerous seeds are then spread very rapidly via vehicles, water, animals, farm machinery and wind. The species has heavy deleterious impacts on agriculture by decreasing yields. For instance, in Ethiopia, sorghum grain yield was reduced in between 40% and 97% when P. hysterophorus was left uncontrolled throughout the season. It reduces pasture carrying capacity by up to 90%. Due to its invasive capacity and allelopathic effects, it also has detrimental environmental effects by displacing native plant species and transforming the invaded habitats into monocultural shrublands. In addition, the species causes human health problems such as asthma, bronchitis, dermatitis and hay fever. P. hysterophorus in animal feed can also cause dermatitis with pronounced skin lesions, and taints the milk and meat of animals, thereby reducing the value of animal products.
A climatic projection has been undertaken with CLIMEX, using both the native and alien distributions of the species. Roadside surveys were undertaken in Botswana, Ethiopia, South Africa, Swaziland and Uganda to get further data on the distribution of the species to feed into the model.
The CLIMEX projection indicated that additional areas could be colonized by the species in Australia and the Asian-Pacific, as well as in Africa. Furthermore, significant areas of the EPPO region are climatically suitable for P. hysterophorus, the countries suitable for its establishment being: Algeria, Croatia, France, Greece, Israel, Italy, Morocco, Portugal, Spain, Tunisia and Turkey.
McConnachie AJ, Strathie LW, Mersie W, Gebrehiwot L, Zewdie K, Abdureheim A, Abrha B, Araya T, Asaregew F, Assefa F, Gebre-Tsadik R, Nigatu L, Tadesse B ; Tana;T (2010) Current and potential geographical distribution of the invasive plant Parthenium hysterophorus (Asteraceae) in eastern and southern Africa. Weed Research. DOI: 10.1111/j.1365-3180.2010.00820.x