Effects of African Elephant (Loxodonta Africana) Population on Vegetation around Water Points In Arabuko Sokoke Forest, Kilifi County, Kenya
Kinyanjui, Priscilla Wangui
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The African elephants (Loxodonta africana) are keystone species in its ecosystem. They have been ranked by the International Union on Conservation of Nature (IUCN) as vulnerable species and are of high conservation concern. In Kenya, Arabuko Sokoke Forest (ASF) has been ranked as one of the priority areas for elephant population estimates by the IUCN African Elephant Specialist Group. This study aimed at determining the elephant population density and distribution in Arabuko Sokoke Forest and to assess the impacts of elephants on vegetation around water points within the Forest. Elephant population and distribution was determined using the Faecal Standing crop method which incorporates dung decay rate, defecation and dung density. Elephant dung decay rate was determined by identifying and monitoring 59 fresh dung piles at an interval of 7 days until they completely decayed. Dung decay rate was calculated using the reciprocal of mean survival time. Dung density was determined by counting dung piles along 34 line transects each measuring 1 Kilometre systematically placed at an interval of 5 Km from each other and calculated using the DISTANCE Version 7 software. Impacts of elephants on vegetation were determined by laying two 1 Km long line transects on each of the two water points at Arabuko Swamp and Kwa Muiru respectively. On each line transect, 20m by 10m plots were laid at an interval of 100m. On each plot the variables measured and recorded included: The local name, height, diameter at breast height and the rate of utilization of the plant species; in form of browsing and debarking. Linear regression and analysis of variance were used to determine the statistical difference in the variables in relation to distance from water points. The mean survival time for elephant dung pile in Arabuko Sokoke Forest was estimated to be 147.90 (SE ±6.09) while the elephant dung pile decay rate was 0.0068. Elephant dung density (Y) was 1365.4 dung piles/Km2 (95%, CI=931.6 to 2001.2) while the elephant density (E) was 0.51 elephants/km2. Elephant population in Arabuko Sokoke Forest was estimated to be 215 (95% CI=145 to 318). Both height and diameter at breast height (dbh) had a strong negative relationship with distance from Arabuko Swamp (Height: P < 0.0001; r2 =0.605 and dbh:P=0.0038; r2=0.1194 respectively). Around Kwa Muiru water point, there was a strong positive correlation between the distance from water point and height (P<.0001;r2 =0.232) and diameter at breast height (P<0.00; r2 =0.0009). Eighty five (85) plant species were recorded around Arabuko Swamp while around Kwa Muiru water point, 99 plant species were recorded. There was a significant difference in species richness (P=0.023), diversity (P=0.005) and dominance (P=0.41) between the two water points. Plant utilization by elephants around the two water points was associated with browsing than debarking. Around Kwa Muiru, browsing was higher with 77.8% of the plant species recorded being browsed compared to 68.2% browsed plant species around Arabuko Swamp. Debarking was high around Arabuko Swamp compared to Kwa Muiru water point with 62.4% and 47.5% of the total plant species recorded being debarked respectively. Compared to other studies done to determine elephant population in Arabuko Sokoke Forest, this study shows that there is an increase in elephant population from the previous estimates. It is therefore vital to continue monitoring their population and the associated ecological effect they have on vegetation on temporal and spatial scale.