Spatial synchrony of the two‐year cycle budworm outbreaks in central British Columbia, Canada

Abstract

R. I. 2003. Spatial synchrony of the two-year cycle budworm outbreaks in central British Columbia, Canada. -Oikos 102: 146-154.Outbreaks of forest defoliating insects are usually synchronized over a large spatial scale. Observed records of past outbreaks are usually short and incomplete, therefore long proxy data are useful for better understanding of the spatial synchrony. In this study, we developed tree-ring proxy records of two-year cycle spruce budworm (Choristoneura biennis Freeman) outbreaks in central British Columbia, Canada, and examined the spatial patterns of past outbreaks. This budworm is a major defoliating insect of the interior spruce (Picea engelmannii Parry × P. glauca Moench) and subalpine fir (Abies lasiocarpa [Hook.] Nutt.) forests in the Prince George Region of British Columbia. Four outbreaks occurred in relatively close synchrony over the entire region in the period 1880-1999, however, the initiation year, the intensity and extent of outbreaks varied spatially and from one outbreak to another. In some instances, the occurrence of outbreaks was restricted to only one area. The general synchrony of outbreaks suggested that a large-scale extrinsic factor, such as weather, was at play. However, the imperfect synchrony of outbreaks suggested that local stand characteristics, such as canopy structure, composition of tree species and host plant quality, probably played a major role in preconditioning outbreaks. Dispersal might play a role in synchronizing outbreaks, but the extent to which it contributed to the synchrony was limited in this mountainous region.Q. Cold and Arid Regions En6ironmental and Engineering Research Institute, Chinese Academy of Sciences,

Comparative ecology of conifer-feeding spruce budworms (Lepidoptera: Tortricidae)

“…These reveal that the spruce budworm has been resident in northern forest ecosystems of Canada for at least 8500 years and outbreaks have been recurrent for at least the past four centuries. There is also evidence of outbreaks of western and two-year cycle spruce budworms for several centuries (Zhang and Alfaro 2002;Alfaro et al 2014). Interpreting these patterns assembled from a combination of direct and indirect evidence gathered at different scales and variable sampling intensities is hazardous in detail (Régnière and Lysyk 1995) but nonetheless represents our best evidence of historical population patterns.…”

“…Historical evidence for budworm outbreaks has been reconstructed by study of growth rings in trees (e.g., Blais 1954Blais , 1965aBurleigh et al 2002;Zhang and Alfaro 2002;Alfaro et al 2014), lumber in old buildings (Krause 1997;Boulanger et al 2012), insect remains in sediments (Simard et al 2006), and defoliation surveys (Kettela 1983;Volney 1988;Parfett et al 1994;Simpson and Coy 1999). These reveal that the spruce budworm has been resident in northern forest ecosystems of Canada for at least 8500 years and outbreaks have been recurrent for at least the past four centuries.…”

Northern range limit mountain pine beetle outbreak dynamics in mixed sub-boreal pine forests of British Columbia

“…We then fit a spline curve with a frequency response period of 20 years over each series and tested 10 year windows of forward to backward spline values for years with a doubling of radial growth. The spline helped to remove the effects of sudden, short-term suppression/recovery events, while the 10 year window and 200% release threshold ensured that flagged events would be sufficiently longer and higher in magnitude than typical budworm recoveries (Zhang and Alfaro 2002) or responses to interannual climate variability. The length of the final release chronologies was determined by the interval containing at least 5 recording trees.…”

“…This produced corrected index series emphasizing only deviations from baseline growth unique to the disturbed sites. This is common practice in outbreak reconstructions for defoliators such as the two-year cycle budworm (Zhang and Alfaro 2003), larch sawfly (Girardin et al 2001) and western spruce budworm (Campbell et al 2006) which use a non-host species to remove the influence of climate. Our method differed in that we were able to use same species as a control because canopy mortality events can be readily identified in the field.…”

“…It has been successfully used to study the disturbance dynamics of defoliators (Swetnam and Lynch 1993, Speer et al 2001, Zhang and Alfaro 2002 foliar pathogens (Welsh et al 2009), and a number of bark beetle species (Veblen et al 1991b, Stuart et al 1989, Berg et al 2006. For MPB, evidence of past outbreaks can be found directly through the dating of pine mortality events and indirectly in the accelerated radial growth response of surviving individuals in the affected stand.…”