PROCEEDINGS: Index of Abstracts
HERBIVOROUS INSECTS AND CLIMATE CHANGE: POTENTIAL
CHANGES IN THE SPATIAL DISTRIBUTION OF FOREST DEFOLIATOR OUTBREAKS
1-USDA Forest Service, Northeastern Forest Experiment
Station, Newtown Square, PA 19073. 2-USDA Forest Service, Northeastern
Forest Experiment Station, Morgantown, WV 26505.
The geographical ranges and spatial extent of outbreaks of herbivorous
insect species are likely to shift with climatic change. We investigate
potential changes in spatial distribution of outbreaks of the western
spruce budworm, Choristoneura occidentalis Freeman, in Oregon and
the gypsy moth, Lymantria dispar (L.), in Pennsylvania using maps
of historical defoliation, climate, and forest composition in a
geographic information system. Maps of defoliation frequency were
assembled using historical aerial reconnaissance data. Maps of monthly
means of daily temperature maxima and minima and of monthly precipitation
averaged over 30 years were developed using an interpolation technique.
All maps were at a spatial resolution of 2 H 2 km. Relationships
between defoliation status and the environmental variables were
modeled using a linear discriminant function. Five climatic change
scenarios were investigated: an increase of 2 EC, a 2 EC increase
with an increase of 0.5 mm per day in precipitation, a 2 EC increase
with an equivalent decrease in precipitation, and equilibrium projections
of temperature and precipitation by two general circulation models
(GCMs) at doubled CO2 levels.
With an increase in temperature alone, the projected defoliated
area decreased relative to ambient conditions for the budworm and
increased slightly for the gypsy moth. With an increase in temperature
and precipitation, the defoliated area increased for both species.
Conversely, the defoliated area decreased for both when temperature
increased and precipitation decreased. Results for the GCM scenarios
contrasted sharply. Using the scenario projected by the Geophysical
Fluids Dynamics Laboratory (GFDL) GCM, defoliation by budworm was
projected to cover Oregon completely, whereas no defoliation was
projected by gypsy moth in Pennsylvania. Under the scenario projected
by the Goddard Institute for Space Studies (GISS) GCM, defoliation
disappeared completely for the budworm and slightly exceeded that
under ambient conditions for the gypsy moth. The results are discussed
in terms of potential changes in forest species composition.