Description

Abstract: The study was conducted in Jijiga, Kebribeyah and Harshin districts of the Jijiga Zone, Somali Regional State of Ethiopia. The objectives of the study were to assess the perception of the pastoralists on the effects of parthenium, to analyze the impact of parthenium on herbaceous plant composition and diversity, to determine spatial abundance of parthenium in soil seed bank flora compared to the other herbaceous species, to relate the flora of soil seed bank with the composition of the standing vegetation and to evaluate the ability of selected forage species to compete with parthenium. The data required to know pastoralists’ perceptions of the impact of parthenium were collected through structured questionnaire, group discussion and visual observations. A total of 200 quadrats (1mx1m) in 20 sample sites were used to collect data on herbaceous vegetation and soil seed bank flora. Based on the obtained data, the rangeland was stratified into five categories, i.e. none, very low, low, moderate and high parthenium infested sites. Then, the competitive ability of the selected forage species was evaluated and aboveground biomass of all species was collected. According to the respondents, parthenium reduces the carrying capacity of the grazing land by reducing the composition as well as the diversity of palatable species. The study revealed also that the weed adversely affects the quality of milk and meat, and Generally jeopardizes animal products and their markets. The weed has a harmful effect on human as well as animal health in the study area. A total of 63 herbaceous species in 20 families were identified in five infestation levels. Out of which 41, 41, 33, 23 and 22 herbaceous species were found in NIS (None Infested Site), VLIS (Very Low Infested Sites), LIS (Low Infested Sites), MIS (Moderately Infested Sites) and HIS (High Infested Sites), respectively. Out of the identified total species, the proportion of grasses were 62.72, 62, 55.93, 39.97, and 16.6% in NIS, VLIS, LIS, MIS and HIS, respectively. Similarly, the proportion of parthenium was 0, 1.5, 14.27, 30.72, and 66.98% in NIS, VLIS, LIS, MIS and HIS, respectively. The study suggested that in all infestation levels Asystasia schimperi, Cassia occidentalis, Cynodon dactylon, Eragrostis papposa, Chrysopogon aucheri, Ocimum basilicum and Tragus berteronianus had better proportion than the other herbaceous species .On the other hand, Erucastrum arabicum and Euphorbia hirta had better proportion in HIS than the other sites. The species composition of (grasses and forbs), aboveground biomass, evenness and the diversity indices were found to be significantly different (P<0.05) among the infestation levels. The highest number of the variables was obtained in NIS and the least at HIS. What is more, the study indicated that they percentage of parthenium was negatively correlated with xvii species composition, aboveground biomass and evenness and to the diversity indices. The total number of species in the soil seed bank was 59 and all of them belong to 16 families. Out of these, 81.62, 6.7 and 1.96% were herbaceous, woody herb and tree species, respectively. The most dominant species were Eragrostis papposa, Digitaria abyssinica and Parthenium hysterophorus in NIS, VLIS and LIS, MIS and HIS, respectively. Parthenium hysterophorus accounted for 0.58, 7.39, 54.46, 87, and 94% in NIS, VLIS, LIS, MIS and HIS, of the total species recoded, respectively. The diversity and evenness of the species among the infestation levels in soil seed bank showed significant (P<0.05) difference. The highest species diversity was obtained at VLIS whereas the least was found at HIS. The two way ANOVA made on seedling density along depths and between sites revealed a significant (P<0.05) difference. Similarly, the similarity between above ground vegetation and species in soil seed bank between infestation levels showed significant (P<0.05) differences across the infestation levels. The highest mean similarity was obtained at NIS and the lowest at HIS. The ability of grass species to compete with parthenium measured on crowding coefficient and an aggressivity index showed that Bothriochloa insculpta strongly out competed parthenium. This was followed by Cenchrus ciliaris, Cynodon dactylon, Panicum coloratum and Chloris gayana. Taking into account the variations between infestation levels, one can conclude that Parthenium hysterophorus exerted harmful impacts on the composition, diversity and biomass production of the grass species in the rangelands of the study area. The study suggested again that grasses are able to out compete up to a level greater or equal to the density of parthenium. It revealed also that the condition of a species' ability to compete might point out that proper use of grazing management practices would minimize rangelands' risk of infestation by parthenium.