Assessing the effects of post‐pine beetle forest litter on snow albedo

Abstract

The effect of forest litter on snow surface albedo has been subject to limited study, mainly in the hardwood-dominated forests of the northeastern United States. Given the recent pine beetle infestation in Western North America and associated increases in litter production, this study examines the effects of forest litter on snow surface albedo in the coniferous forests of south-central British Columbia. Measured changes in canopy transmittance provide an indication of canopy loss or total litterfall over the winter of 2007-2008. Relationships between percent litter cover, an index of albedo, snow depth, and snow ablation during the 2008 melt season are compared between a mature, young, and clearcut coniferous stand. Results indicate a strong feedback effect between canopy loss and subsequent enhanced shortwave transmittance, and litter accumulation on the snow surface from that canopy loss. However, this relationship is confounded by other variables concurrently affecting albedo. While results suggest that a relatively small percent litter cover can have a significant effect on albedo and ablation, further research is underway to extract the litter signal from that of other factors affecting albedo, particularly snow depth.

Albedo-induced radiative forcing from mountain pine beetle outbreaks in forests, south-central Rocky Mountains: magnitude, persistence, and relation to outbreak severity

“…Despite wide recognition of the large extent and severity of recent MPB outbreaks, an assessment of the decadal persistence of albedo and radiative forcing effects, as well as an exploration of the impact of outbreak severity on those effects, are both still lacking. Existing studies have documented a decrease in winter albedo in the early attack stages due to needle and litter accumulation on snow (Winkler et al, 2010;Pugh and Small, 2012) and an increase in winter albedo after needle fall, presumably due to the increased visibility of snow (O'Halloran et al, 2012;Vanderhoof et al, 2013). The persistence of winter albedo changes in existing studies has been limited to ∼ 15 yr post-outbreak when albedo change remains large.…”

Spatiotemporal variation of surface shortwave forcing from fire-induced albedo change in interior Alaska

“…First, some trees that might be severely damaged but not killed immediately by the fires could still keep most of the dead needles and branches for 1-2 years before falling to the floor; this structure is similar to the "red attack stage" of the mountain pine beetle (Dendroctonus ponderosae Hopkins, 1902). Existing studies based on Landsat and MODIS (Vanderhoof et al 2014) have documented a decrease in winter albedo in this stage due to needle and litter accumulation on snow (Winkler et al 2010;Pugh and Small 2012). Second, snow might melt faster in some recently burned areas, leading to shorter snow duration and thus a prolonged exposure of burned soil (Liu et al 2005).…”

Climate-driven disturbances in the San Juan River sub-basin of the Colorado River

“…Causes of the reported changes have been related to topography (Schnorbus et al, 2010) and climate variability . Other reported causes are secondary impacts occurring as a result of forest mortality that enhance processes such as radiation (Royer et al, 2011;Varhola et al, 2010), changes in albedo (Winkler et al, 2010), evapotranspiration (Zou et al, 2010;Kang et al, 2006), groundwater availability (Bearup et al, 2014, and soil moisture states (Dale et al, 2001). Snow has been reported to play an important role in changes in streamflow (Solander et al, 2017;Bennett et al, 2015) through increased snow accumulation and snowmelt (Bewley et al, 2010;Boon, 2007), snow cover duration (Boon, 2009), reduced interception, canopy sublimation, and evapotranspiration in disturbed forests (Livneh et al, 2015b).…”

“…Snow also melts quicker in response to increased shortwave radiation and turbulent heat transfers linked to negative longwave radiative fluxes (Burles and Boon, 2011). The responses have also been linked to decreased albedo due to higher litter and/or darker soils associated with dying trees (Bewley et al, 2010;Winkler et al, 2010). Other effects of tree mortality on the water balance include changes to soil moisture states, changes in groundwater recharge , and potential feedbacks to the atmosphere (Bonan, 2008).…”