I’ve written on a number of occasions on Briffa’s Polar Urals reconstruction, which is used in nearly every multiproxy reconstruction, no doubt because of its uniquely cold MWP. It’s one of the key series in Crowley and Lowery  and Jones et al ; it’s not as important in MBH98-99 (which is more or less just the bristlecones in the MWP. Here’s some information from a relatively inaccessible source: Shiyatov, S.G. Reconstruction of climate and the upper treeline dynamics, Publications of the Academy of Finland 6/95, 144-147.
The full article is posted up here. It says (and this sure sounds different than Crowley):
From the middle of the 8th to the end of the 13th, there was intense regeneration of larch and the timberline rose up to 340 a.s.l. The 12th and 13th centuries were most favorable for larch growth. At this time the altitudinal position of the timberline was the highest, stand density the biggest, longevity of trees the longest, size of trees the largest, increment in diameter and height the most intensive as compared with other periods under review.
Here’s a diagram (rotated from the original) showing the height of the medieval trees as contrasted with the modern trees.
Figure 1. Height of Polar Urals Trees (Shiyatov, Acad. Finl)
By comparison, here is Briffa’s reconstruction, which hardly seems to represent the same area. Briffa’s reconstruction shows a cold period around AD1200, while this is the time of the highest treeline in the entire record.
Figure 2. Briffa’s Polar Urals Temperature Reconstruction
For someone supposedly concerned with low-frequency changes, you’d think they’d pay some attention to the altitude of the trees. I’ve tried unsuccessfully to get data on the altitude of individual cores to do a more detailed study. I really do have an interest in this stuff; I’m not pounding on unarchived data for the sake of pounding on it. I’ve had a practical interest in it or I wouldn’t have inquired.