Linking Climate with Invasive Species Dynamics on the Landscape

R. Talbot Trotter, Michael Montgomery and Kathleen Shields

USDA Forest Service Northeastern Research Station

 Outside the issues of host specificity and non-target effects, the effective and efficient use of biological control methods depends on two specific pieces of information: 1) knowing where (and when) the biocontrol agent is needed; and 2) knowing where (and when) it can establish.  Over the last few decades, the hemlock woolly adelgid (HWA) has become a prime target for biological control programs, as chemical controls have proven to be impractical at landscape scales because of both ecological and logistical problems.  To date, at least ten species of arthropods have been imported to the U.S., and several have been released in the eastern U.S. for the control of HWA.  To date however, successful establishment of the species in varying locations has been erratic.
Risk mapping and climate/landscape modeling offer opportunities to improve our understanding of factors related to successful establishment of invasive pests and their biocontrols.  Previous HWA risk mapping has focused on the distribution of the host species, providing the critical baseline estimate for the potential maximum distribution of the species.  However, the expressed distribution may differ as a result of both biotic and abiotic factors such as temperature limits.  The spread of HWA populations in the late 1990s provides a possible example of temperature acting as a limiting factor in pest establishment.  Prior to 1998, HWA populations were largely limited to the eastern aspect of the Appalachian Mountains.  Estimation of minimum January temperatures across the landscape using data from ~1600 weather stations (available from NOAA NCDC) in combination with county infestation records suggests the high altitudes of the Appalachians produced a cold barrier to establishment of HWA.  However, regional weather data shows that around 1998, warmer-than-average winter temperatures may have provided a temporal window in this barrier, allowing the HWA to expand rapidly west.  Patterns such as these provide insight into the dynamics of species movements across the landscape, and provide a starting point for the prediction of the expected limits of establishment for the invasive species - a key to understanding where biological control is likely to be needed.

corresponding author:

R. Talbot Trotter III
Northeastern Center for Forest Health Research
51 Mill Pond Road
Hamden CT 06514
203-230-4312
rttrotter@fs.fed.us