Reviewing the bidding: at Niwot Ridge, a short drive from UCAR world headquarters, we have disparate chronologies from Graybill and Woodhouse for limber pine at similar elevations (with Graybill’s chronology also discrepant from nearby chronologies from Kienast and Schweingruber for very close PCEN series). Despite the disparate appearances, the correlation between the Graybill and Woodhouse chronologies was a surprisingly high 0.46.
To shed a little more light on this, I’ve plotted up spaghetti graphs and grassplots for the measurements by individual trees. On the left is Woodhouse (co511) and on the right is Graybill (co545). As you can see, the Woodhouse sample has a lot of trees which started growing in the 15th century, while the Graybill sample has trees starting later. The majority of the Woodhouse trees have a fast start; the Graybill sample has quite a few cores with elevated 20th century ring widths – which are not present in the Woodhouse sample.
Both samples appear to have 2 cores per tree. The Woodhouse sample has trees numbered up to 21, lists 21 unique trees and shows 40 cores. The Graybill sample has trees numbered up to 18, but only lists 15 unique trees and only shows 27 cores. Auditors never like missing invoice numbers.
Pat Frank wondered whether the differences might result from the construction of the ecological station – who knows? However, the 20th century ramp is typical of Graybill series and I’d be more inclined to think that it results from something in Graybill’s methodology, as opposed to the sewage. Remember that Graybill was seeking out strip-bark trees: I’d be more inclined to think that the answer lies there. For example, Graybill and Idso  showed a difference between strip-bark and whole-bark trees in the 20th century at Sheep Mountain. I’ll check, but I’ll bet that the difference is comparable to the difference between Woodhouse and Graybill here.
But something is sure different between these series. You’d think that someone from UCAR world headquarters in Boulder would put down their latte and find out.