Treeline in the Arctic

As promised, I'm going to consider the Arctic Treeline for this next post. Just as a warning, one of the papers I use in this post includes some sites from below the 66 degrees latitude level, so I hope you'll forgive the slight digression from our brief.

An alpine treeline in the background. Although not an Arctic treeline,
the clear change illustrates the concept well.

Firstly, what is the Arctic treeline? As an intuitive general definition, a treeline separates regions where tree-growth is sustainable, and areas where climatic factors such as low temperatures prohibit the establishment

Shrubland expansion - photographic evidence

To start off the posts on terrestrial ecosystem change, I'd like to share a short (one page!) correspondance article from Nature by Sturm et al (2001). It's pretty simple and is completely qualitative based on only two 'observations', but it's interesting nonetheless. The authors found high quality photographs, taken during oil reserves exploration in 1949 at around 68° latitude in the Alaskan Arctic. By taking 66 modern photographs at some of the same locations, they could compare the vegetation cover at the same sites over the 50 year period. Here's one of the comparisons:


A hillside in the Alaskan Arctic in 1949 and 2000. A and B show identical locations.

Although a crude assessment, it is clear that there is a difference between the two photographs. Abundance