Snow was monitored for five years in plots from which 30% of the timber had been previously removed in the form of group selection and in an unlogged control at a sub-alpine site in British Columbia. Average peak snow water equivalents (SWE) ranged from 38 to 52 cm and occurred between late March and mid-April. Canopy density was measured in circular areas of sky in 10-degree increments from the zenith to the horizon. The optimum parameter for explaining the variability of peak SWE was canopy density within a 60-to 80-degree-wide cone. Results suggest that where openings are 1 ha or less, peak SWE approached a locally consistent maximum value when canopy density approached zero. This improves our ability to predict the effects of group selection on snow accumulation in high elevation forests.Key words: forest canopy, snow interception, snow accumulation, group selection La quantité de neige a été mesurée pendant cinq ans dans des parcelles où 30 % du bois avait été extrait sous forme de sélection de groupe d'arbres et dans des parcelles témoins non exploitées sur une station sub-alpine de la Colombie-britannique. Les quantités maximales équivalentes en eau de la neige ont varié de 38 à 52 cm et se sont produites entre la fin mars et la mi-avril. La densité du couvert forestier a été mesurée par des superficies circulaires du ciel augmentant par tranches de 10 degrés à partir du zénith jusqu'à l'horizon. Le paramètre optimal pour expliquer la variabilité de la quantité équivalente en eau maximale était la densité du couvert comparable à un cône de 60 à 80 degrés de largeur. Les résultats suggèrent que lorsque les ouvertures sont d'un hectare ou moins, la quantité équivalente en eau maximale s'approchait d'une valeur maximale localement constante lorsque la densité du couvert était proche de zéro. Ceci améliore notre capacité à prédire les effets de la sélection par groupe d'arbres sur l'accumulation de la neige dans les forêts de hautes altitudes.

Concentrations of the major cations and silica were monitored in four small British Columbia CoastMountain streams during the 1976 snowmelt season. The four streams could be grouped into three unique classes using logarithmically transformed calcium and potassium concentrations. The two most similar basins fed streams that were chemically indistinguishable. The next most similar basin yielded runoff that was chemically similar to the other two except for unusually low K + concentration, possibly due to a shortage of biotite in the bedrock. The fourth stream had unusually high Ca + +, Mg + +, Na +, and silica concentrations due to the long residence time of groundwater from metamorphic rocks in its basin. Another different feature of that basin was the earlier depletion of its spring snowpack due to its south aspect. Time-variant differences in chemistry among streams were measured as changing ratios of solute concentrations over time. Differences among streams were time-variant due to time variance of interbasin runoff components. The relative contribution of groundwater increased in the basin with the metamorphic rocks and decreased in the other three basins over the summer. The chemical differences among streams were reflected in solute loads as well as solute concentrations. Therefore the major components of variable runoff and solute sources in the study area were high runoff and low solute yield from three basins on granite and low runoff but high solute yield from a basin on metamorphic rocks. INTRODUCTIONThe major controls of stream chemistry under natural conditions were identified by Gorham [1961] as climate, geology, topography, biota, and time. Although lithology and climate have more recently been identified as the dominant factors by some authors [e.g., Garrels and MacKenzie, 1971; Gregory and Walling, 1973], this is partly a result of the scale at which comparisons have been made. In comparing large rivers draining basins with rather different runoff and/or geology, it is not surprising that biologic and topographic factors would appear to be less important. However, the variables are statistically confounded, a situation that is well illustrated by Gibbs [1967], who accounted for 78% of the variability of dissolved solids in Amazon basin tributaries by the surrogate variable "relief' and found that 86% of the total solute load was derived from the mountainous headwaters which comprised only 12% of the drainage area. The importance of organic reactions and ecosystems in the mobilization, uptake, storage, and release of solutes to streams is well documented [e.g., Johnson et al., 1969; Cleaves et al., 1970; Edwards, 1973; Johnson, 1975; Freeze and Cherry, 1979, p. 117]. However, there have been few studies that have identified biologic differences as the controlling factor in chemical differences between streams. During periods of nonequilibrium, net changes in biomass chemical budgets have caused changes in stream chemistry. Feller [1976] observed increases in stream solute concentrations after logg...

We evaluated the suitability of several different instruments for surveying stream shade, selected one as most suitable for our purposes, and tested its accuracy. Five different operators used the instrument to estimate shade as angular canopy density (ACD), canopy density above 60°,, and canopy density above 80° in two plots—one in a mixed-age coniferous stand and one in a mixed-age deciduous stand. We compared operator estimates (ocular method) with measurements from fisheye photographs (computer-fisheye method). In a random coefficients regression model, the effect of “plot” on regression slopes and intercepts was not significant at α = 0.05. The regression line for ACD by the ocular method versus the computerfisheye method had a slope of 0.87 and an intercept of 0.02. The slope was significantly different from 1 at α = 0.05, indicating a tendency for human operators to underestimate ACD. Estimates of mean ACD on the two plots by individual operators were 2–11 percentage points lower, respectively, than mean ACD calculated from fisheye photos and the effect of operator was highly significant (ρ < 0.0001). Operators who received 45 minutes of training performed better than did an operator who received 15 minutes of training. Results suggest that operator variability is a large potential source of error in ocular estimates and that an investment of at least 1 hour of formal training may be worthwhile. The errors associated with any ocular-type canopy density measuring instrument should be documented before it is used to make statistical inferences.

These findings are relevant to watershed management be-

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