Some biological characteristics that foster the invasion of Prosopis juliflora (Sw.) DC. at Middle Awash Rift Valley Area, north-eastern Ethiopia

• Published in: Journal of arid environments 2004-07, Vol.58 (2), p.135-154
• Main Authors: Shiferaw, Hailu, Teketay, Demel, Nemomissa, Sileshi, Assefa, Fassil
• Format: Article
• Language: English
• Subjects: animal droppings; animal manures; buried seeds; coppicing; Droppings; feces; invasive species; noxious weeds; Pods; Prosopis juliflora; seed density; Seed dispersal; seed germination; Seed germination and coppicing ability; seed productivity; seeds; semiarid zones; Socio-economy and impacts; Soil seed bank; spatial distribution; viability
• ISSN: 0140-1963; 1095-922X
• DOI: 10.1016/j.jaridenv.2003.08.011

A study on some biological features of Prosopis juliflora, a multipurpose leguminous species introduced to Ethiopia, was carried out at Melka-Worer, North-east Ethiopia. The study focused on the number of seeds produced in a pod during the study period, seed dispersal through droppings of animals, soil seed banks, seed germination and stumping height of trees and coppicing ability of P. juliflora. The overall mean number of seeds was 23±4 seeds/pod. The width and length of seeds ranged between 0.8–1.7 and 8–29 cm, respectively. The mean weight of a seed of Prosopis was 0.0275 g±0.001 (S.E.) while there were 36,000–37,000 seeds/kg. The number of seeds recovered from 1 kg of droppings of each animal ranged between 760 (goats) and 2833 (cattle), suggesting that cattle are the major dispersers of seeds of the study species followed by warthogs, camels and goats. There was a highly significant difference in vertical distribution of the seed density of P. juliflora recovered from the soil samples while the horizontal distribution exhibited a great disparity in the density of soil seeds among the sample plots. The total mean soil seed density, in the litter layer and down to 9 cm depth, was 1932 seeds/m 2 (±307 S.E.). Germination of seeds of P. juliflora differed significantly among the various treatments. The highest germination percentage was obtained from seeds that were treated with mechanical scarification (100%) and sulfuric acid for 15–60 min (97–99%). About 37% and 47% of the seeds recovered from droppings of goats and warthogs, respectively, germinated. All stumped trees of P. juliflora produced coppices except those stumped at 10 cm below ground. The overall mean number of coppices at the studied plots was 17.8±0.9 (S.E.) while the overall mean height of coppices, in 6 months after stumping, was 68.4 cm±2.7 (S.E.). The results clearly demonstrated that Prosopis is equipped with a number of biological characteristics that foster its rapid invasion of new areas. These include: (i) production of many, small and hard seeds capable of surviving passage through the digestive system of animals, entering into the soil to form soil seed banks and remaining viable until favorable conditions for germination and seedling establishment appear; (ii) attractive and rewarding pods for animals, containing fleshy and sweet mesocarp embodying the numerous small seeds, which is sought after by both domestic and wild animals, meant for long-distance dispersal; (iii) accumul