Another angle on denrochronology.
Climate Audit is doing stirling work re-examining tree ring data to see what they tell us about the past climate. There has been quite a bit of discussion as to how damaged bark areas affect subsequent ring growth. To help you visualise it here is one of my logs.
Click for larger version
As you can see twenty years ago something happened to the tree and the resultant rings are uneven. If you imagine coring the tree from different angles you can see how very different data would be obtained. From some places it would show a definite increase in growth, and hence warmer temperatures, and from others a constant or decreasing rate.