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Soil moisture in seasonally snow‐covered environments fluctuates seasonally between wet and dry states. Climate warming is advancing the onset of spring snowmelt and may lengthen the summer‐dry state and ultimately cause drier soil conditions. The magnitude of either response may vary across elevation and vegetation types. We situated our study at the lower boundary of persistent snow cover and the upper boundary of subalpine forest with paired treatment blocks in aspen forest and open meadow. In treatments plots, we advanced snowmelt timing by an average of 14 days by adding dust to the snow surface during spring melt. We specifically wanted to know whether early snowmelt would increase the duration of the summer‐dry period and cause soils to be drier in the early‐snowmelt treatments compared with control plots. We found no difference in the onset of the summer‐dry state and no significant differences in soil moisture between treatments. To better understand the reasons soil moisture did not respond to early snowmelt as expected, we examined the mediating influences of soil organic matter, texture, temperature, and the presence or absence of forest. In our study, late‐spring precipitation may have moderated the effects of early snowmelt on soil moisture. We conclude that landscape characteristics, including soil, vegetation, and regional weather patterns, may supersede the effects of snowmelt timing in determining growing season soil moisture, and efforts to anticipate the impacts of climate change on seasonally snow‐covered ecosystems should take into account these mediating factors. Copyright © 2015 John Wiley & Sons, Ltd.

Tree mortality because of beetle outbreaks has become substantial and widespread in conifer forests in western North America. A number of environmental and physiological factors influence patterns of mortality. Tree diversity may reduce the severity and extent of insect damage to host trees by providing associational resistance, but the existence and importance of associational resistance varies by forest type and by tree and insect species. We assessed whether plot-level tree diversity contributed to survival of Engelmann spruce (Picea engelmannii Parry ex Engelm.) following a spruce beetle (Dendroctonus rufipennis Kirby) epidemic. Our study plots comprised 2 to 5 tree species including Engelmann spruce, subalpine fir (Abies lasiocarpa (Hook) Nutt.), Douglas-fir (Pseudostuga menziesii (Mirb.) Franco), quaking aspen (Populus tremuloides Michx.), and white fir (Abies concolor (Gordon & Glend.) Hildebr.). We used a model-selection analysis to compare the importance of tree diversity with other known factors that influence spruce survival. We found lower rates of spruce survival in stands where spruce was the dominant tree species (by percent of stand density index) and higher survival in stands where nonspruce conifers (Douglas-fir, subalpine, and white fir) were dominant. We also found that tree diversity (Shannon index) did not show a positive correlation to spruce survival and that there was no additional benefit derived from the presence of aspen, which has higher phylogenetic distance from Engelmann spruce than the other trees in this study. The relationship between diversity and survival is complicated by factors that naturally co-vary with diversity, such as elevation, aspect, and stand density of spruce. Our results best support an explanation that if associational resistance does increase spruce survival during a beetle epidemic, it is due to host or resource dilution, which may be an indirect effect of higher stand diversity.Résumé : La mortalité des arbres due à des épidémies de scolytes est devenue importante et très répandue dans les forêts de l'ouest de l'Amérique du Nord. Plusieurs facteurs physiologiques et environnementaux influencent les patrons de mortalité. La diversité des espèces d'arbre peut réduire la sévérité et l'étendue des dommages causés par les insectes sur les arbres hôtes en procurant une résistance d'association mais l'existence et l'importance de la résistance d'association varient selon le type de forêt et l'espèce d'arbre et d'insecte. Nous avons déterminé si la diversité des arbres à l'échelle de la parcelle contribuait à la survie de l'épicéa d'Engelmann (Picea engelmannii Parry ex Engelm.) à la suite d'une épidémie de dendroctone de l'épinette (Dendroctonus rufipennis Kirby). Nos parcelles expérimentales comprenaient 2 à 5 espèces d'arbre incluant l'épicéa d'Engelmann, le sapin subalpin (Abies lasiocarpa (Hook.) Nutt.), le douglas de Menzies (Pseudotsuga menziesii (Mirb.) Franco), le peuplier faux-tremble (Populus tremuloides Michx.) et le sapin concolore (A. concolor (Gordon ...