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.

Site preparation alleviates the effects of pinegrass (Calamagrostis rubescens Buckl.) interference on conifers in British Columbia, but little is known about interference mechanisms and appropriate site preparation methods for steep slopes. In this study, lodgepole pine (Pinus contorta Dougl. ex Loud.) was planted in pinegrass controls and small (90 × 90 cm) and large (180 × 90 cm) patches where (i) only pinegrass was removed using glyphosate or (ii) both pinegrass and the forest floor were removed using an excavator. Treatments were replicated three times in east-and west-facing clearcuts and effects were followed for 9 years. Two-year pine survival was 78% in the control and >97% in large patches. All patch treatments improved pine growth, but it was greatest in large chemical patches during the initial 6 years and in both large patch treatments thereafter. Removal of the forest floor reduced foliar and soil nutrients, increased bulk density and soil water availability, decreased porosity and aggregate stability, and reduced ectomycorrhizal diversity and richness. These changes were not observed in chemical patches. All patch treatments increased soil temperatures and reduced frost relative to controls, but more so in large patches. Pinegrass can suppress early pine performance, and large chemical patches that retain the forest floor are best for relieving the multiple environmental stressors.Résumé : La préparation de terrain réduit l'interférence causée par Calamagrostis rubescens Buckl. sur les conifères de la Colombie-Britannique, mais les mécanismes d'interférence et les méthodes de préparation de terrain appropriées pour les pentes fortes demeurent peu connus. Dans cette étude, des pins de Murray (Pinus contorta Dougl. ex Loud.) ont été plantés dans des parcelles témoins avec Calamagrostis, des petits placeaux (90 × 90 cm) et des grands placeaux (180 × 90 cm) où le Calamagrostis avait été éliminé (i) en utilisant le glyphosate seulement ou (ii) en enlevant aussi la couverture morte avec l'aide d'une excavatrice. Les traitements ont été répétés trois fois dans des coupes à blanc faisant face à l'est et à l'ouest et les effets ont été suivis durant 9 ans. La survie des pins après 2 ans était de 78 % dans les témoins et supérieure à 97 % dans les grands placeaux. Tous les traitements en placeaux ont amélioré la croissance du pin, mais l'effet le plus important a été observé dans les grands placeaux traités à l'herbicide au cours des six premières années, et dans les deux traitements en grands placeaux par la suite. L'élimination de la couverture morte a réduit la concentration en éléments nutritifs dans le sol et le feuillage, a augmenté la densité apparente et la disponibilité en eau du sol, a réduit la porosité et la stabilité des agrégats, et a réduit la diversité et la richesse des ectomycorrhizes. Ces changements n'ont pas été observés dans les placeaux traités à l'herbicide. Tous les traitements en placeaux ont augmenté la température du sol et réduit les gelées en comparaison avec les témoins, mais de...

No abstract

This study quantified changes in snow accumulation and ablation with forest defoliation in a young pine stand attacked by mountain pine beetle, a mature mixed species stand, and a clearcut in south‐central British Columbia. From 2006 to 2012, as trees in the pine stand turned from green to grey, average canopy transmittance increased from 27% to 49%. In the mixed stand, transmittance remained constant at 19%. In 2009, the year of greatest needle loss, average snow surface litter cover in the pine stand was 29% (range 4 – 61%), compared to ≤9% in other years and over double that in the mixed stand. By 2012, litter accumulation in the now‐grey pine stand was only a sixth of that in the mixed stand. Inter‐annual variability in the weather had the greatest effect on snow accumulation and ablation, with the greatest differences between both forested stands and the clearcut occurring in 2010, the year of lowest SWE. Differences in snow accumulation between the pine and mixed stand increased in 2010 as a result of decreased snow interception in the young stand after needlefall. Average ablation rates in the attacked stand were most different from the mixed stand in 2009 and 2012, the years with the largest and smallest over‐winter needle loss, respectively. This study shows that grey, non‐pine, and understory trees moderate snow response to changes in the main canopy. It also highlights the complex interrelationships between ecohydrological processes key to assessing watershed response to forest cover loss in snow dominated hydrologic regimes. Copyright © 2012 John Wiley & Sons, Ltd.

Long-term studies at Mayson Lake (ML) and Upper Penticton Creek (UPC) in British Columbia's southern interior quantify snow-dominated hydrologic response to natural disturbances and logging. Following natural disturbance at ML, changes in snow accumulation related directly to mountain pine beetle attack were measurable by the fifth year following attack, when canopy transmittance had increased 24% due to needlefall. In year 1, April 1 snow water equivalent (SWE) was 48% higher in the clearcut than in the pine forest. This difference was reduced to 23% by year 8. A 3-year lag in snow response was also observed in a nearby burned stand where SWE was on average 27 and 59% higher in the clearcut than in the burn and forest, respectively. At UPC, April 1 SWE averaged 12% more and 12% less in a low and high elevation clearcut than forest, respectively, and snow disappeared ∼10 days earlier in both clearcuts. Partially as a result of snowmelt synchronization from higher with lower elevations after 50% of the treatment watersheds had been clearcut, April water yield increased and June to July yield decreased. Research results improve evaluation of hydrologic response to forest disturbance, including retention of beetle-killed stands versus salvage logging.