Results/Conclusions: The empirical evidence of no tree regeneration is from more than 100 openings of ~1 to 4 tree heights in diameter. These small gaps were created more than 50 years ago by hydrologists to increase snow accumulation and extend the spring melt to increase spring runoff. Other openings greater than ~4 tree heights in diameter (wildfires) have trees recruit within 5 years of the opening being created. In the small openings the apparent reason no trees have re-established is the persistence of more than 1 to 2 meters of snow into the spring so that tree seedlings have a much-reduced growing season and are often infected by snow fungus (spp.). The processes that explain the snow accumulation are: 1) in small openings the low sun angle (in these northern latitudes) and surrounding canopy height shade the shortwave radiation from reaching into these small openings while the outgoing longwave radiation has no barrier to the sky, producing a cold hole which allows snow to accumulate; 2) in large openings both shortwave and longwave radiation contribute to snow melt; 3) in closed canopies longwave radiation dominates causing surface snow melt, and shortwave radiation causes snow caught in the conifer canopies to be lost by sublimation. This snow accumulation and delayed melt in small openings is at least one explanation for not finding patch dynamics in these northern forests. Southern deciduous and northern hardwood forests do not have snow accumulation in small openings because higher sun angles and the mostly leafless trees in winter allow more shortwave radiation to penetrate to the forest floor and melt the snow.
