SNOWFALL INTERCEPTION ON BRANCHES OF 3 CONIFER SPECIES

Measuring the mass of snow on cut branch tips soon after snowfalls during two winters provided comparisons of catch by Engelmann spruce (Picea engelmannii Parry), subalpine fir (Abies lasiocarpa (Hook.) Nutt.), and lodgepole pine (Pinus contorta var. latifolia Engelm.). Analysis of these and other reported measurements confirmed (i) snow bridging by cohesion, (ii) bouncing of snow crystals by elastic rebound, and (iii) branch bending as mechanisms that determine the sigmoidal growth curves characterizing snow interception relative to snowfall. The fraction of snowfall intercepted by the branches was largest when storm accumulations were 3-4 mm water equivalent, with low specific gravity (0.04-0.07). Percent catch in snowfalls with 10 mm water and low specific gravity was near 50% for Engelmann spruce and about 45% for subalpine fir and lodgepole pine, but values decreased to near 30% in 20-mm storms. Catch was inversely proportional to the density of snow accumulations in the specific gravity range 0.04-0.13. Average branch catch was only about 10% of a storm with 10 mm water equivalent at 0.13 specific gravity. Meterological conditions were more important than branch growth form in determining snow interception amounts on the conifers tested. The results suggest, as a hypothesis, a computational function for the fraction of snowfall caught on conifer crowns.