“Past episodes of unfavorable climate led to the death of the most marginal individuals (those within approximately 100 m of tree line; Lloyd & Graumlich 1997), while leaving individuals short distances from the edge (100-200m) unaffected (this study).”

Lloyd (Fig 2) shows peak per capita mortality occurring during the megadrought of AD1150, at a rate of 0.09/50 years. I note that death rates for “marginal” and less marginal trees would not need to differ by much to produce strong survivorship bias in the tree-ring record.

Further to #34. See:

Horsley, S.B., Long, R.P., Bailey, S.W., Hallett, R.A., and Hall, T.J. 2000. Factors associated with the decline disease of sugar maple on the Allegheny Plateau. Can. J. For. Res. 30: 1365–1378.

Horsley, S.B., Long, R.P., Bailey, S.W., Hallett, R.A., and Wargo, P.M. 2002. Health of Eastern North American Sugar Maple Forests and Factors Affecting Decline. Northern Journal of Applied Forestry 19: 34-44.

Bourque, C., Cox, R., Allen, D., Arp, P., Meng, F. 2005. Spatial extent of winter thaw events in eastern North America: historical weather records in relation to yellow birch decline. Global Change Biology 11 (9): 1477-1492.

Each finger “root storage carbohydrates” as the mechanism by which Mg/Mn nutrition, soil thaw-freeze events, and insect defoliation cause hardwood decline.

One wonders whether bcp “storage carbohydrates” (roots or foliage) might be part of:
-the 20th c. uptick in annual growth of strip-bark forms
-the divergence problem (positive and negative responders)
-drought-caused decline of high-elevation pines

Surprised no one has mentioned “megadroughts” here yet. Sounds like the kind of thing that could burn up bristlecone pines, thus forcing them out of the tree-ring record.

http://tinyurl.com/ewpac