Ideas and perspectives: use of tree-ring width as an indicator of tree growth.

By taking core samples, dendroecological studies can reconstruct radial growth over the lifespan of a tree, providing a valuable way to estimate the sensitivity of tree productivity to environmental change. With increasing prevalence of such studies in global change science, it is worth cautioning that the incremental growth rate of a sub-dimension of a tree organ, such as annual ring width (w), does not respond to extrinsic perturbations with the same relative magnitude as the primary production of that organ. For example, if an extrinsic force causes a two-fold increase in the absolute growth rate of stemwood biomass (AGR), it should only theoretically translate into a 1.3-fold increase in w, or a 1.7-fold increase in basal area increment (BAI), when a 2 : 1 ratio in resource allocation to lateral and apical meristems is assumed. Expressing the magnitude of a response in relative terms does not, therefore, provide a valid means of comparing estimates of relative growth derived from measurement of different dimensional traits of the tree. From our perspective, enough conformity to facilitate comparison of environmental sensitivity across studies of tree growth is warranted so we emphasize the benefit of dimension analysis to transform measurements of w and BAI into the AGR. Although conversion to AGR introduces an error from the use of allometric equations, the approach is widely accepted in mainstream ecology and global change science at least partially because it avoids discrepancies in response magnitude owing to differences in dimension. Studies of organ elongation have historically provided invaluable information, yet it must be recognized that they systematically underestimate the response magnitude of primary production, and confound comparisons of growth sensitivity between many dendroecological studies that focus on w and studies of primary production. [ABSTRACT FROM AUTHOR]