Abstract
Abstract. Forest cover modifies snow accumulation and ablation rates via canopy interception and changes in sub-canopy energy balance processes. However, the ways in which snowpacks are affected by forest canopy processes vary depending on climatic, topographic and forest characteristics. Here we present results from a 4-year study of snow–forest interactions in the Oregon Cascades. We continuously monitored snow and meteorological variables at paired forested and open sites at three elevations representing the Low, Mid, and High seasonal snow zones in the study region. On a monthly to bi-weekly basis, we surveyed snow depth and snow water equivalent across 900 m transects connecting the forested and open pairs of sites. Our results show that relative to nearby open areas, the dense, relatively warm forests at Low and Mid sites impede snow accumulation via canopy snow interception and increase sub-canopy snowpack energy inputs via longwave radiation. Compared with the Forest sites, snowpacks are deeper and last longer in the Open site at the Low and Mid sites (4–26 and 11–33 days, respectively). However, we see the opposite relationship at the relatively colder High sites, with the Forest site maintaining snow longer into the spring by 15–29 days relative to the nearby Open site. Canopy interception efficiency (CIE) values at the Low and Mid Forest sites averaged 79 and 76 % of the total event snowfall, whereas CIE was 31 % at the lower density High Forest site. At all elevations, longwave radiation in forested environments appears to be the primary energy component due to the maritime climate and forest presence, accounting for 93, 92, and 47 % of total energy inputs to the snowpack at the Low, Mid, and High Forest sites, respectively. Higher wind speeds in the High Open site significantly increase turbulent energy exchanges and snow sublimation. Lower wind speeds in the High Forest site create preferential snowfall deposition. These results show the importance of understanding the effects of forest cover on sub-canopy snowpack evolution and highlight the need for improved forest cover model representation to accurately predict water resources in maritime forests.
Highlights
Events that lasted for a single day had an average canopy interception efficiency of 87 % with a reduction in average Canopy interception efficiency (CIE) with increasing event length, from 73 % for a 2-day event and 57 % for a 3-day event to 51 % for any event lasting longer than 4 days
We note an apparent threshold behavior where events less than 15 cm have a stronger linear relationship between event size and CIE (Fig. 3) and the canopy was more effective at snow removal for events in that range compared with events greater than 15 cm
This paper highlights the complex snow–forest process relationships and suggests that forest cover is a principal control on snow persistence due to reduced accumulation from canopy interception and earlier/faster melt due to increased longwave radiation
Summary
A considerable amount of effort has been expended in research into the snow–forest processes that control the distribution of snow in mountainous regions (Stähli and Gustafsson, 2006; Jost et al, 2007; López-Moreno and Latron, 2008; Musselman et al, 2008; Ellis et al, 2013; Moeser et al, 2015) While these studies have focused on cold, predominately continental snowpacks, few have investigated snow–forest process interaction in warm maritime environments where snow is especially sensitive to changes in energy balance (Storck et al, 2002; Lundquist et al, 2013)
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