Assessment of the impact of land use practices on vegetation , soil and carbon-nitrogen sequestration potential in Mopane rangelands of Central Northern Namibia

This study was conducted in Ogongo district, situated in Omusati Region of the central northern Namibia. The objectives of this study were to assess the impact of land use practices on 1) vegetation distribution and status; 2) soil properties; 3) carbon-nitrogen sequestration potential, and 4) investigate the indigenous pastoralists’ knowledge and perceptions on livestock production, rangeland degradation and its indicators in three villages (Omaandi, Epukunoyana and Oshitutuma) in Mopane savannah rangelands of central northern Namibia. For vegetation and soil assessment, three grazing land management systems (communal, game reserve and cattle ranch) were identified adjacent to each other. In each grazing system, three sites (for game reserve and cattle ranch, these were camps) were selected. In each site, three belt transects of 50 m x 5 m2 were marked to record vegetation and soil data as well as to collect vegetation samples for analysis. Grass species composition was recorded using step point methods from 250 points per belt transect. A total of five 0.25 m2 quadrats were randomly laid within each 250 m2 belt transect to record the herbaceous plant density, tuft diameter, tuft distance and biomass. All woody plants in the belt transect (250 m2) were measured and recorded for species plant height and canopy diameters. Three soil samples per belt transect were collected at the time of forage sampling down to a depth of 20 cm using a soil auger. Soil and plant samples were analysed for macro and micro minerals, total organic carbon, total nitrogen, carbon-nitrogen ratios, and carbon and nitrogen isotopes. For bulk density, soil samples were collected using soil core samplers. In the social study, a total of 90 households were randomly selected from three villages and a total of 48 elders were purposefully selected based on the age, time spent in the village and livestock ownership. A combination of structured and semi-structured questionnaires were used to gather household information, while a structured questionnaire and open ended discussion were used to interview elders on the constraints of livestock production, rangeland degradation related issues and their consequences on livelihood. Field vegetation and soil data were analyzed using a General Linear Model (GLM) in SAS (2007), whereas the social data were analyzed using SPSS version 21 (2014). A total of 23 grass species were identified in all three land management systems, of which 48% were perennials and the remaining 52% were annuals. Aristida meridionalis dominated the game reserve and the ranch, whereas Eragrostis trichophora was dominant in all land management systems. Forbs occurred commonly in the game reserve and the ranch, but were dominant in the communal areas. The abundance of A. meridionalis responded significantly (P 0.05) between the three land management systems. Woody plant density of height classes were significantly different (P 0.05) concentrations in soils obtained from all land management systems in both seasons. Soil Calcium (Ca) levels showed differences between land management systems in winter only being greater (P ranch > communal area and the trend was similar in both seasons. In summer, the game reserve had the greatest (P 0.001) δ15N values. In summer, both the communal and ranch had slightly higher (P 0.05) differences between land management systems. Soil δ13C level was remarkably (P < 0.05) affected by land management systems, but did not interact with seasons. In both seasons, the communal land had slightly higher (P < 0.001) δ13C level than the other two land management systems. In both seasons, δ15N levels showed great differences (P < 0.001) between land management systems, with highest soil δ15N levels observed in the communal area than the ranch and game reserve. Results on social survey showed that the majority of the interviewed households in Omaandi (63percent), Oshitutuma (53percent) and Epukunoyana (50percent) were female headed families and the remaining were male headed. The mean population of goats and cattle were significantly higher (P < 0.05) in Omaandi and Epukunoyana than in Oshitutuma village, respectively. In this study, household respondents in all villages indicated that all livestock species were primarily kept for wealth status and provision of meat for consumption. Respondents in all villages also indicated that lack of grazing lands and shortage of feed were the primary constraints of livestock production followed by water scarcity and recurring droughts. Elder respondents in all villages perceived overgrazing and climate change as the primary cause of rangeland degradation. Elder interviewees in Omaandi and Oshitutuma villages regarded low grass cover and dominance of poor quality grass (Epukunoyana only) as the primary vegetation indicators of rangeland degradation. The animal related indicators such as stunted animal body as a result of mineral deficiency, high livestock mortality, emaciated body and animals traveling long distance for grazing and water (Oshitutuma only) were regarded in all villages as the primary livestock related indicators of rangeland degradation. Elders from Epukunoyana village ranked low rainfall, high soil and atmospheric temperatures as the primary climate related indicators of rangeland degradation, although in Omaandi and Oshitutuma, high soil and atmospheric temperatures were considered as the primary climate related indicators of rangeland degradation. Based on the findings, this study concludes that land management systems had great influences on the distribution and production of herbaceous and woody vegetation in summer and winter seasons. This study also observed that land management systems interacted strongly with season to influence most vegetation and soil variables. Lastly, based on the study findings, the study concludes that all three communal rangelands are degraded and degradation led to a gradual declining trend in the livestock population over the past 10 to 20 years in the communal areas as a result of feed shortage