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WILL GLOBAL WARMING ALTER PAPER BIRCH
SUSCEPTIBILITY TO BRONZE BIRCH BORER ATTACK?
ROBERT A. HAACK
USDA Forest Service, North Central Forest Experiment Station
1407 S. Harrison Road, East Lansing, M148823, USA
INTRODUCTION
According to several general circulation models, a rapid climatic warming of 1-5°C in the annual global-mean surface
air temperature is predicted by the year 2050 (Shands and Hoffman 1987, MacCracken et al. 1990, Karl et al. 1991,
Schlesinger and Jiang 1991, IPCC 1992, Peters 1992, Bengtsson 1994). Some forest entomologists predict an increase in
outbreak frequency of certain forest insects as a result of global warming (Kellomaki et al. 1988, Hedden 1989, Franklin et
al. 1992, Fleming and Volney 1995), although the actual response may be difficult to predict due to the many interacting
biotic and abiotic factors (Hedden 1989, Porter et al. 1991, Cammell and Knight 1992, Dewar and Watt 1992, Ayres 1993,
Scriber and Gage 1995, Williams and Liebhold 1995).
Is there a way to test whether climate change will alter tree susceptibility to insect attack? One method is to look for
patterns of differential insect attack within genetic test plantations where trees of known genetic background grow together at
the same test site. Frequently, the primary objective of genetic test plantings is to identify either specific families or geographic
seed sources (provenances) that performed well at a particular location, especially with respect to growth and form
characteristics. The trees in genetic test plantings, particularly provenance tests, commonly originate from several distant
locations, often representing several contrasting climates. Because tree populations become genetically adapted to their local
conditions, one major factor that affects their performance when moved to a new location is the difference in climate between
the original and the new location (Wright 1976, Kozlowski et al. 1991, Schmidtling 1994). Data from genetic test plantings
have only recently been examined to elucidate how some tree species might respond to global warming (Matyas 1994,
Schmidtling 1994). Similarly unexplored has been the use of provenance plantation data to predict how global warming will
affect tree susceptibility to insect attack.
In this paper, I explore how global warming might alter susceptibility of paper birch, Betula papyrifera Marsh., to the
bronze birch borer, Agrilus anxius Gory (Coleoptera: Buprestidae). This particular tree-insect combination was selected
because (1) paper birch appears highly sensitive to environmental stress given that several large scale declines of paper birch
have been reported this century in eastern North America, and (2) the bronze birch borer has usually been the ultimate
mortality agent of stressed birch trees (Slingerland 1906, Swaine 1918, Spaulding and MacAloney 1931, Balch and Prebble
1940, Hawboldt 1947, Nash et al. 1951, Barter 1957, Redmond 1957, Clark and Barter 1958, Haack and Mattson 1989, Jones
et al. 1993, Braathe 1995). Birch mortality as a result of bronze birch borer attack has followed stress events such as drought,
extreme cold winter temperatures that follow closely behind a winter thaw, elevated growing season temperatures, high soil
water tables, years of heavy seed crops, and years of severe insect defoliation (Redmond 1955, 1957; Clark and Barter 1958;
Herms 1991; Herms and Mattson 1991; Auclair et al. 1992; Jones et al. 1993; Auclair et al. 1995; Braathe 1995).
Paper birch is a boreal species, and in Michigan it reaches its southernmost range near the center of Michigan's lower
peninsula. The ecotone between boreal and temperate forests closely follows the 47°F (8.3"C) average annual mean temperature
isotherm in Michigan (Fig. 1). Typically, annual mean temperature decreases steadily with increasing latitude, but in
Michigan, the Great Lakes cause a semi-marine type climate, causing isotherms to closely follow the lakes' shorelines (Fig.
1). This feature of moderately vertical isotherms in portions of Michigan allows for great variation in climatic conditions
within a rather narrow latitudinal band. Michigan is relatively flat, ranging in elevation from 174 to 604 m (572-1,980 ft)
above sea level.
Mattson, W.J., Niemel/i, R, and Rousi, M., eds. 1996. Dynamics of forest herbivory: quest for pattern and principle. USDA
For. Serv. Gen. Tech. Rep. NC-183, N.C. For. Exp. Sta., St. Paul, MN 55108.
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