date: Tue, 03 Mar 1998 10:00:15 -0700 from: Connie Woodhouse subject: Nature paper to: Keith Briffa Keith, I found your recent Nature paper on the decreasing sensitivity of tree-growth to temperature in the second half of the 20th century quite interesting. I've been working with a collection of tree-ring chronologies for the Colorado Front Range (you've probably used some of these chronologies in your analysis) and have noted something similar. Although I'm looking at ring widths, and these are more high-elevation than high latitude, I found that most of the higher elevation species (limber pine, lodgepole pine, bristlecone pine) have an inconsistent response to climate. I've been trying to put together a decent regional precipitation reconstruction, so I just deleted those chronologies from my analysis, and have been working with ponderosa pine and Douglas fir, the lower elevation species, which seem to have a stable response to climate. I know Don Graybill noted this inconsistent response with high elevation species when he worked in this area 10 years ago, and he seemed to think the change took place in the 1930s. I haven't looked very closely at these chronologies yet, but this change in response/sensitivity is something I'd like to look at, especially in light of you and your co-authors' findings which suggests a possible hemispheric-scale forcing. Thanks for a thought-provoking paper! Connie Connie Woodhouse NOAA Paleoclimatology Program National Geophysical Data Center 325 Broadway St. Boulder, CO 80303 (303)497-6297 woodhous@ngdc.noaa.gov