DISTRIBUTION AND REPRODUCTIVE BIOLOGY OF THE INVASIVE PLANT Argemone mexicana L. AND ITS IMPACT ON THE LIVELIHOOD OF THE LOCAL COMMUNITY IN SOUTH WOLLO, ETHIOPIA

Abstract

Globally, approximately 17% of valuable ecosystems are impacted by invasive alien species categorized as high or very high threats. The spread of invasive alien plants (IAPs) is exacerbated by changes in climate and land use. Argemone mexicana L. is an IAP that thrives in warm tropical and subtropical climates and can survive in areas with low moisture, disturbed environments, and poor soil nutrients. In Ethiopia, the presence of A. mexicana is increasing, identifying it as a significant IAP. This study focused on the current and future (2050 and 2070) agroecological distributions of A. mexicana. It quantified its density, biomass, fruit, and seed production across farmlands, settlements, roadsides, and grazing lands and between midland and highland agroecology. This study also tests the allelopathic effects of A. mexicana on two crops Cicer arietinum L. and Eragrostis tef (Zucc.) Trotter, and grasses Eragrostis japonica (Thunb.) Trin. and Urochloa brachyura (Hack.) Stapf (1920), seed germination and seedling growth and assessed their impacts on household livelihood income in South Wollo, Ethiopia. Stratified sampling methods were employed to sample the study sites and households. A total of eight kebeles and 384 households were sampled from two districts covering two agroecologies. The data were analyzed via various statistical approaches, including ensemble species distribution models (SDMs), one-way ANOVA, Tukey’s HSD test, independent t-tests, and propensity score matching (PSM) logit models. The analytical tools used included Arc-GIS 10.7.1, R4.2.1, and STATA14 software. The results indicated that A. mexicana potentially occupies an agroecological range from the midland (1500 masl) to the sub-alpine (3700 masl), both currently and in future projections (2050 and 2070). The total suitable agroecological area currently accounts for 23.26% of the total area. In the future, under the three Shared Socioeconomic Pathways (SSPs) projected climate change scenarios, SSP1-2.6(low), SSP2- 4.5(intermediate), and SSP5-8.5(very high) total suitable agroecological areas will be 28.67%, 27.29% and 25.15% by 2050 and 24.35%, 28%, and 21.14% by 2070, respectively. The mean density of A. mexicana varied significantly, ranging from 22,450 to 75,833 individuals per hectare across different land uses (p < 2e-16, f = 262.1) and from 39,208 to 46,219 based on xxiii agroecological conditions (t = 2.6981, df = 379.27 p = 0.007286). The aboveground fresh biomass measured between 0.556 kg/m² to 2.41 kg/m² (p < 2e-16, f = 87.29) and 1.247 kg/m² to 1.594 kg/m² (t = 3.3049, df = 151.7 p = 0.001186), for land use and agroecology respectively. Belowground fresh biomass ranged from 0.129 kg/m² to 0.343 kg/m² (p < 4.33e-12, f = 22.35), and 0.135 kg/m² to 0.233 kg/m² (t = 3.8362, df = 104.81, p = 0.0002138), for land use and agroecology respectively. For aboveground dry biomass, values varied from 0.049 kg/m² to 1.22 kg/m² ( p < 3.28e-11, f = 37.74 ) and 0.379 kg/m² to 0.689 kg/m² (t = 3.4117, df = 146.39, p = 0.0008347), while belowground dry biomass ranged between 0.093 kg/m² to 0.313 kg/m² (p < 4.33e-11, f = 22.35) and 0.106 kg/m² to 0.203 kg/m² (t = 3.8307, df = 104.2, p = 0.0002187), for land use and agroecology respectively. The mean number of fruits per A. mexicana ranged from 23 to 76 (p < 2e-16, f = 274.7) and 36 to 52 (t = 10.186, df = 1535.6, p = 0.0001) across land use types and agroecological settings respectively. Additionally, the seed count per fruit varied from 345 to 384(p < 2e-06 , f = 9.861) and 352 to 377(t = 5.5824, df = 1320. 3, p = 0.0001), depending on land use and agroecology, respectively. The A. mexicana roots, stems, and leaves had allelopathic effects on the seed germination and seedling growth of C. arietinum and E. tef, crops and, E. japonica, and U. brachyura grass species’. Argemone mexicana invasions affected households by significantly reducing their livelihood income from crops and livestock production. The estimated average treatment effect on the treated (ATT), from the entire A. mexicana-invaded sample households showed that their incomes decreased annually, by - 3764.7 Ethiopian Birr (ETB), SE = 1832.6, t = -3.09, p = 0.010. The agroecological distribution potential of A. mexicana in South Wollo, Ethiopia, is bound above 1500 masl and below 3,700 masl. Agroecologies found below 1,500 masl and above 3,700 masl are unsuitable for A. mexicana distribution in current and future periods. The density, biomass, fruit, and seed production of A. mexicana are not the same across farmlands, settlements, roadsides, and grazing land uses and between the midland and highland agroecology. In the farmlands and the midlands, agroecology had the highest mean values, whereas it had the lowest mean values in the grazing land and highland agroecology. Their distribution is favorable and depends on climate change and land use type or change. It has an allelopathic inhibitory effect on the tested crops and grasses in the order of leaf > stem > root. It has an impact on the livelihood income of the household obtained from crop and livestock production. Effective coordination among xxiv local community, government, and non-government bodies is needed to minimize the agroecological distribution potential of A. mexicana in South Wollo, Ethiopia