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A NEW METHOD TO RECONSTRUCT BARK BEETLE OUTBREAKS: RECURRENCE INTERVALS AND HISTORY OF SPRUCE BARK BEETLE (DENDROCTONUS RUFIPENNIS) INFESTATION IN SOUTHWEST YUKON, CANADA

SEIFERLING, IAN S  Univeristy of Regina, Saskatchewan.
Vetter, Mary  University of Regina.

It is widely accepted today that disturbance is a major force structuring vegetation mosaics (De Grandre et al. 1993) by altering vegetation composition and processes of the system. Spruce bark beetles (Dendroctonus rufipennis) are considered a major force of disturbance in boreal forest ecosystems as they have the potential to remove large proportions of the forest canopy. Outbreaks of these pests are of great concern because it appears that the patterns of beetle attacks are changing. Evidence suggests that the size, level of tree mortality, and frequency of outbreaks may be increasing as of the last few decades (Ross et al. 2001). Garbutt (2000, pers comm.) observed that the current outbreaks in the Yukon Territory and Alaska have already outlasted all of the known historic spruce bark beetle attacks that have occurred in British Columbia. Yet we know surprisingly little about the influence of these outbreaks on forest dynamics (Veblen et al. 1991), and the historical record of spruce beetle activity is presently limited to tree ring data (dating back two to three centuries in the Yukon and up to five centuries in the Rockies) and written records that only reach back to the 1800s in North America. Bark beetles will typically attack and kill all mature spruce trees within the infested area. Subsequently, all of the needles on these trees will fall off about one year after being attacked. If an infested spruce stand occupies the land within a lake’s basin, many of these needles will presumably be transported into the lake waters where the needles will break down. The stomata from conifer needles are very resistant to decomposition and are typically reworked from shallow into deep regions of lakes and preserved in these sediments. The massive influx of needles from an infested stand around lakes should produce a long-term proxy record of spruce bark beetle outbreaks in the area. A sediment core was extracted from a small lake within the Kluane Lake region of the southwest Yukon in order to determine the historic occurrences, recurrence intervals, and levels of past spruce bark beetle outbreaks in this currently infested area. The core was sectioned at 3 mm intervals to provide high temporal resolution over the past 900 years. A 1 cc sub-sample from each sample was processed to extract fossil stomata using standard pollen extraction techniques (Faegri et al., 1989). Fossil stomata will then be identified and counted on slides under light microscope. A select fewer samples will be analysed for beetle remains as per the kerosene flotation method (Elias, 1994) and hand picked bark beetle fragments from the samples will be identified. Bark beetle remains, found in the sediments which stomata concentrations have indicated outbreaks, would confirm the presence of an outbreak. The concentration of conifer stomata of each sample will be extrapolated from slide counts and plotted over time. I expect a large rise in stomata concentrations, over that of the immediately previous years, will indicate the occurrence of spruce defoliation and thus bark beetle infestation. This research is needed to establish the recurrence intervals of bark beetles and, to not only relate these data to other proxy indicators (e.g. pollen and charcoal and dendrochronology) of vegetation, fire history, and climate, but to also shed light onto the possible effects of climate change on insect pests and forest disturbance dynamics.

REFERENCES
De Grandpre Louis, Gagnon Danieal, and Bergeron Yves, 1993, Changes in the understory of Canadian southern boreal forest after fire: Journal of Vegetation Science, v.4, p. 803-810.



Elias, S.A., 1994, Quaternary Insects and Their Environments: Smithsonian Institution Press, Washington and London. 284 pp.



Faegri, K.J., Iverson, J., Kaland, P.E., and Kryzwinsnki, K., 1989, Textbook of Pollen Analysis 4th Edition: Toronto, Wiley, 328 pp.



Ross Darrell W {a}, Daterman Gary E, Boughton Jerry L, and Quigley Thomas M., 2001, Forest health restoration in south-central Alaska: A problem analysis: US Forest Service Pacific Northwest Research Station General Technical Report PNW-GTR.



Veblen T T {a}, Hadley K S, Reid M S, and Rebertus A J., 1991, Methods of Detecting Past Spruce Beetle Outbreaks in Rocky Mountain USA Subalpine Forests: Canadian Journal of Forest Research, v. 21, p. 242-254.


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