This thesis attempts to determine to what extent fluvial allogenic factors affect the development of vegetation in the Lillooet Valley, north-west of Pemberton, B.C. Microenvironments exist within the floodplain, based on height, flood frequency, drainage conditions, tree cover and soil development. The area is in a constant state of flux with respect to the change of species over time and the associated nature of the river channels that cause new areas to become available while constantly destroying other vegetated areas. The major hypothesis that vegetation, both individual species and species groups, can be spatially related to elevation differences as a measure of flood frequencies, cannot be proved in isolation from other hypotheses. Mo species were found to be solely related to the elevation factor. Although six species were found to be significantly related to height, they can only be used in very general terms to estimate flood frequency, however, as it is the rare 15 to 50 year event that determines the major vegetation pattern. Pioneer, scrub and young deciduous forests on the lower elevations and the understorys of the mature forests are entirely destroyed by such an event, thus changing the direction and pace of the development of many sites markedly. The second hypothesis was that sediment type as a measure of drainage conditions is important in differentiating species distribution, especially at the pioneer stage. It has been successfully demonstrated that during initial species invasion sediment type is important. This initial spatial differentiation causes major species variation in young forests and these differences may still be noticeable in mature coniferous forests. Finally, the importance of time and associated autogenic processes was noted to be of importance. It has been shown that there are several species groups existing within the field area that reflect the age of the sediment surface, and that the sites must be discussed within the age groups for meaningful results. / Arts, Faculty of / Geography, Department of / Graduate