Vulnerability of white spruce with slowly expanding lower boles on dry, cold sites to early seasonal attack by spruce beetles in south central Alaska

Abstract

Two stands of white spruce (Piceaglauca (Moench) Voss), one on a south aspect and one on a north aspect on the Kenai Peninsula of Alaska, were sampled intensively to determine site and host variables associated with high attack densities by spruce beetle, Dendroctonusrufipennis (Kirby). Attacks peaked during the early phase of tree radial growth on both aspects as the rate of tree expansion slowed. Generally, the first trees attacked, also the most heavily attacked, expanded more slowly before and after beetle attack than did trees attacked later or not at all. High attack densities were concentrated in trees on dry, cold soils. Mean percent basal-area growth of plots was inversely related to stocking of live spruce and to percentage of sample trees attacked and killed.

Spruce beetle outbreaks on the Kenai Peninsula, Alaska, and Kluane National Park and Reserve, Yukon Territory: Relationship to summer temperatures and regional differences in disturbance regimes

“…Spruce beetles concentrate their attack on mature spruce in the late spring when trees experience seasonal drought stress because cold or partially frozen soils retard water uptake and precipitation is normally low (Hard, 1987). Spruce on southfacing slopes are typically less prone to infestations by spruce beetles than spruce growing on north-facing slopes because of warmer soil temperatures (Hard, 1987).…”

“…Spruce on southfacing slopes are typically less prone to infestations by spruce beetles than spruce growing on north-facing slopes because of warmer soil temperatures (Hard, 1987). However, during warm summers, excessive heat causes drought stress of white spruce on south-facing slopes and can cause radial growth to slow (Barber et al, 2000.…”

“…Spruce beetles selectively attack mature spruce, because large, slow-growing spruce are less able to resist the establishment of adult spruce beetles in the inner bark or phloem layer (Hard et al, 1983;Hard, 1987). After the overstory spruce are killed by spruce beetles, the smaller surviving spruce have less competition for light, soil moisture, and nutrients, and often increase their growth abruptly (Veblen et al, 1991a,b).…”

Spruce beetles and forest ecosystems in south-central Alaska: A review of 30 years of research

“…Spruce beetles initially colonize only a few highly susceptible spruce within stands before soils completely thaw and the temperature threshold is reached to elicit mass dispersal by spruce beetles. As air and soils warm, the spruce adjacent to these initial points of attack are subsequently infested by emerging adult spruce beetles with spruce located further from the ''focus trees'' attacked at lower rates (Hard, 1987(Hard, , 1989.…”

Cross-scale Drivers of Natural Disturbances Prone to Anthropogenic Amplification: The Dynamics of Bark Beetle Eruptions

“…For example, temperature, precipitation, and tree physiology interact to synchronize the flight activity of these short-lived adults with relatively brief windows of host vulnerability that are associated with seasonal drought stress (Bentz et al 1991, Hansen and Bentz 2003, Berg et al 2006. Likewise, winters with low snow cover can delay thawing of spruce roots, which reduces their ability to translocate defensive resins during peak spruce beetle emergence (Hard 1987). At an even finer scale, temperature can determine the relative success of various mutualistic versus antagonistic microbial symbionts (Six and Bentz 2007).…”