D1: Oral Presentation C Thursday, 10:30 � 11:00 am C Lake Superior Ballroom MN

Predicting Tree Species Range Limits

Karen V. Walker
University of Minnesota
Department of Forest Resources
Remote Sensing and Geospatial Analysis Laboratory
115 Green Hall
1530 Cleveland Avenue North
St. Paul, MN  55108
kwalker@gis.umn.edu

Margaret B. Davis, Shinya Sugita
University of Minnesota
Department of Ecology, Evolution and Behavior
100 Ecology Building
1987 Upper Buford Circle
St. Paul, MN  55108
 

Range limits of ten important timber trees in the Great Lakes Region were predicted using an equilibrium model (STASH). STASH uses bioclimatic variables to predict a spatial �envelope� of suitable climate for each species. A ten-minute grid of bioclimatic variables derived from weather records was obtained, and contour lines were created using ArcView. The contours were overlaid on digitized maps of current species range limits. Contour lines coincided well with species range limits; values along these lines were chosen as minimums or maximums tolerated by the species to establish the climate-space envelope for that species. 

Potential future shifts in species ranges under climate change scenarios were predicted using climate data from two general circulation models (CGCM1 and HadCM2). Monthly predictions for the years 1994-2099 were obtained on a 0.5-degree grid. Bioclimatic variables were derived from the raw data, and interpolated onto the same ten-minute grid used for current climate using a distance-weighted average. Additional adjustments were made to account for differences between modeled �current� climate and observed current climate.

A comparison of contour lines of observed and predicted bioclimatic variables illustrates the mechanisms behind the predicted changes in species range limits. Trees with southern range limits within the Great Lakes region, including white, jack, and red pine, aspen and yellow birch are predicted to retreat northward due to increasing summer temperatures. Trees that currently occur in both the northern and southern portions of the region (red oak, sugar maple, and beech) are expected to remain in the region. Trees with northern range limits within the Great Lakes region are predicted to gain potential habitat to the north due to increases in growing degree-days, and coldest month temperatures. However, retreating species will likely die off sooner than expanding species will be able to migrate into newly suitable area, potentially leaving less diverse forests.