Quantification of change in forest structure before and after the confinement of Elephants (Loxodanta Africana, Blumenbach) in Arabuko Sokoke forest

Abstract

Incidents of human-wildlife conflict emanating from farm raids by elephants and baboons led to the construction of an electric fence in Arabuko Sokoke Forest (ASF). Consequently, wildlife was confined and this has aggravated localized ecological degradation, particularly around the watering points. However, the aforementioned impacts have not yet been quantified. In this study, anniversary satellite images before and after fencing were acquired and processed using ERDAS and Arc GIS software. Normalized Difference Vegetation index (NDVI) was used to assess vegetation change dynamics which were categorized into three forest change types (positive, negative and no change). Samples from each of the NDVIs were randomly selected and their coordinates fed into Global Positioning System (GPS) and used to establish transects to ascertain the status quo and associated factors. To assess the impact of prolonged elephant browsing near water points, four diverging line transects measuring 4 kilometers each were made from three major watering points. Nested plots were laid along each transect and vegetation data collected. Graduated elephant vegetation damage score ranging from no damage (0) to high damage (5) was used to assess elephant's impact on vegetation in the plots. Variation in elephants' impacts on vegetation was evaluated using Analysis of Variance (ANOVA). The area under negative change increased at rate of2.4 ha per annum resulting to a decrease in areas under positive and no change. There was a significant difference in tree height (p<0.001), Diameter at Breast Height (DBH) (p<0.001) and tree density (p=0.04) in all the three forest change types. The intensity of elephant induced damage was highest in areas under negative change. A significant difference in DBH (p=0.04) was observed along water point-forest gradient. Tree density did not vary significantly along water point-forest gradient. Tree debarking by elephants was significantly different along the water point-forest gradient (p=0.03) in all the water points. The number of trampled trees did not vary significantly (p=O.35) along water point-forest gradient in the three water points. These findings show that confinement of elephants in Arabuko Sokoke forest has negatively affected the forest structure and exacerbated destruction of the forest ecosystem. There is need to develop measures that can reduce the pressure of elephants on vegetation in the forest for conservation of biodiversity and provision of ecosystem services.