Fig. 4.

Upslope shift of the ecotone between northern hardwood and boreal forest. The location of the ecotone is shown in 1962, 1995, and 2005 for Camels Hump (A) and Mount Abraham (B). The black points represent the normalized pixel values (z scores) from aerial photographs or satellite images for pixels along narrow transects that cross from northern hardwood to boreal forest. Higher pixel values are indicative of northern hardwood forests. Identical transects were examined in all 3 years for each mountain. The blue line represents the smoothed model fit to these data, and the red dashed lines represent the estimated change-point locations, which delineate the ecotone. The arrows in the 2005 graphs indicate elevations where northern hardwood species have moved into former areas of boreal forest.