SCALE, DIRECTION, AND PATTERN IN RIPARIAN VEGETATION ENVIRONMENT RELATIONSHIPS

Because of the linear nature of riparian environments, direction and scale are closely linked. Cross-valley variation in mountain stream valleys is typically seen on a scale of meters, while variation up- and down-valley may be measured in kilometers. As a result, environmental factors at transverse scale (varying within a cross section) and at longitudinal scale (varying between cross sections) impose different patterns on vegetation. This paper compares these scale influences on the composition of woody riparian vegetation in southern California. Using cover data from 37 valley cross sections in the Transverse Ranges, and dividing these into four-meter segments, I determine segment values for the longitudinal-scale variables of elevation, years since burning, aspect, valley width and lithology, and for the transverse-scale variables of water-table depth, unit stream power (for the 20-year flood), and substrate particle size. The influence of variables at these contrasting scales on the vegetation composition are compared using detrended correspondence analysis, principal components analysis, multiple regression, and analysis of variance. The results show that transverse- and longitudinal-scale variables have significant influences on the vegetation, though neither scale is dominant. All of which suggests that the complex mosaic of riparian vegetation in this environment reflects the coincidence of environmental relationships operating in different directions on contrasting scales.