Figure 1 Variation with height in physiological and structural features of redwood trees at Humboldt Redwoods State Park, California. a, Xylem pressure of small branches measured at predawn (upper group) and midday (lower group) during September and October 2000. The upper line is the expected gravitational pressure gradient with the same y-intercept as the average of the 5 trees. b, Leaf mass:area ratio (g m22) of secondyear internodes increases with height. c, Foliar carbon isotope composition (d13C, ���) increases with height within the crowns of 5 trees over 110 m tall and among the tops (filled circles) of 16 trees from 85 to 113 m tall. d, Light-saturated photosynthetic rate per unit mass (nmol CO g21 s21) decreases with height. The regression line is fitted to data 2 from six trees. Different symbol types denote different trees and are consistent for a���d.

Published as part of George W. Koch, Stephen C. Sillett, Gregory M. Jennings & Stephen D. Davis, 2004, The limits to tree height, pp. 851-854 in Nature 428 on page 851, DOI: 10.1038/nature02417, http://zenodo.org/record/1401032