Diversity and distribution of sedges on multivariate environmental gradients

Abstract

Relationships between environmental factors and the distribution patterns of sedges were studied in the wetland important bird areas of Uganda. Vegetation data were collected using the transect and quadrat methods. Four quadrats were located at each sampling point at 10 m intervals along the transect from dry land to open water. Relative abundances of sedges were recorded in each quadrat. Inventory sampling was done to record species that were not recorded on the transects so as to generate near complete species lists. Human influences on vegetation such as harvesting, fire and vegetation modification were examined along the transects. Soil samples were collected along the transects for analysis of P, K, Na, Ca, Mg and organic matter. Other parameters recorded from water samples included water levels, pH and water conductivity. Rainfall and altitude were also recorded. Canonical correspondence analysis was used to correlate the relative abundances of the species to measured environmental variables. Linear correlation of the environmental variables with principal components indicated that water levels, altitude and rainfall were major factors that influenced the abundance and occurrence of sedges in the different bird areas. Sedge distribution patterns are a function of local geological and edaphic factors; and human-induced exogenous disturbances.