Shoreline vegetation distribution in relation to wave exposure and bay characteristics in Lake Victoria

The concept that wind-wave exposure is a major regulator of vegetation distribution within lakes was investigated. Along a 675 km stretch of shore in northern Lake Victoria (Uganda), the pattern of vegetation distribution in relation to shoreline features, and the variation of shoreline swamp area along a wave exposure gradient were examined. The ability of wave exposure, when combined with bay morphometric characteristics, to predict the lakeward limit of vegetation distribution was assessed. Data was collected through a shoreline survey and from maps. Maximum effective fetch, computed from topographic maps, was used as a surrogate for wave exposure. The results amplify the hypothesis that wave exposure is an important regulator of the within-lake distribution of vegetation. Shoreline plants were found to either occupy stretches of shore shielded by coastal islands or hidden by convolutions of the lake margin. Swamp area declined exponentially with increasing wave exposure and appeared to be affected by the magnitude as well as the frequency of wave disturbance. Of the coastal characteristics examined, bay area had the strongest influence on the lakeward expansion of vegetation. Wave exposure, acting together with bay area and bay aspect ratio, accounted for 65.1% of the variance in the limit of lakeward vegetation advancement.