Temporal relationship between climate variability, Prosopis juliflora invasion and livestock numbers in the drylands of Magadi, Kenya

摘要

A study was conducted to determine the association of climate variability, Prosopis juliflora spread, and other vegetation trends with livestock population dynamics in Kajiado County, Kenya. Monthly rainfall, mean monthly temperatures, cattle, sheep and goats populations from January 2000 to December 2014, were analyzed to determine time series trends. Normalized Difference Vegetation Index (NDVI) data derived from moderate resolution imaging spectroradiometer (MODIS) 250 m satellite imageries for 2000 to 2014 were used to determine the temporal dynamics of P. juliflora invasion in the study area. Both temperature and rainfall trends showed marked variability over the period under study. The mean monthly temperatures during the long dry season increased erratically from 33°C in 2000 to 37°C in 2014. Moreover, the rainfall during the wettest season was 600 mm in 2000 and 250 mm in 2014. During the study period, divergence from the long term mean rainfall (450 mm) decreased from 585 to 403 mm. At the same time cattle population decreased, sheep and goats populations remained static. P. juliflora invasion correlated positively (r=0.2; P0.05) with mean monthly temperature and negatively (r=-0.4; P0.05) with rainfall and other vegetation cover in drier parts, but not in the higher altitude and wetter parts of the study area. It also correlated negatively with cattle populations (r=-0.4; P0.05). In the 1980’s, bushlands and woodlands constituted 95 and 5% of the land cover, while in 2008, herbaceous vegetation, shrublands, and open trees together with bare areas constituted 50, 30, and 22%, respectively; out of which 70% had been taken over by Prosopis in 2014. This study demonstrated that even though the trends showed that cattle population decreased as climate variability and Prosopis invasion increased, there was no significant correlation among the attributes, over the period under study.