The use of fluorescent dye and site characteristics to evaluate surface erosion on harvested areas in the Vernon Forest District, B.C.

Surface erosion on forest lands can cause stream sedimentation and reduce site productivity. In the North Okanagan downstream irrigation and municipal demand require low sediment levels in their water. Higher elevation forest lands have shallow soils developed from nutrient-poor glacial till. To evaluate erosion occurrence on forest lands a research project was initiated in the summer of 1984 on 10 sites in mid-elevation, recently harvested cutblocks in the Vernon Forest Region. The objective of the study was to evaluate surface erosion and relate erosion intensity to site characteristics. Two separate methods were used to accomplish this. Line transects sampled soil disturbance and examined causal factors for erosion occurrence. Fluorescent dye plots, established on four of the 10 sites, examined rate, distance and patterns of downslope soil particle movement. Transects were surveyed in a grid pattern across the cutblock and results indicated areal distribution of disturbance. Soil disturbance at the sample point was recorded using 10 classes ranging from bare soil and litter disturbance to deep gouges and deep deposits of soil. Assessment of care-in-logging and identification of existing and potential erosion sites completed the site evaluation. Day-Glo fluorescent pigment was used to tag soil in situ. Dye was applied in August, 1984, in one metre strips across the slope on plots varying in aspect, slope and disturbance. Field measurement of soil movement was completed in the spring of 1985, shortly after snowmelt. Tagged particles were located and illuminated at night by ultraviolet light. A hand held mineral lamp provided sufficient illumination and fluorescence was recorded on color film. Soil-movement ratings, based on visual perception of particle movement, were assigned to each plot. These ratings were compared to plot and site characteristics to identify possible erosion trends. The results of this study support the consensus of research results reported in the literature. The major sites of erosion are skid trails and the road system. Steep slopes, fine' soil, north aspects and compaction increase potential erosion. Fluorescent dye is an effective soil particle tag allowing distance and pathways of movement to be identified. Day-Glo fluorescent pigment in a solution of acetone was fully satisfactory in adherence to the particle and in persistence under prevailing climatic conditions.Forestry, Faculty ofGraduat