This pair of photos shows the south facing slopes of a small bluff and a riparian corridor cutting through an area likely underlain by permafrost in the flats between the Outer Range and the main escarpment of the Alaska Range near the Teklanika R. An increase in spruce abundance over the 29 year interval between these photos is apparent along the base of a south-facing slope where air and soil temperatures are warmed by solar radiation. Note that the bench areas away from the creek, which are likely on permafrost, have not seen an equivalent increase in spruce abundance. Studies of the factors controlling tree species distribution in Denali suggest that soils in these areas are probably too cold and wet to sustain vigorous growth of white spruce. As a result, changes in the patterns of spruce distribution in treeline areas of the park are likely uneven - occurring more rapidly in areas with warmer soils and higher solar radiation, and more slowly in areas with impeded drainage and cold soils.