THE SCALING OF PLANT HEIGHT - A COMPARISON AMONG MAJOR PLANT CLADES AND ANATOMICAL GRADES

The scaling of plant height h (m) with respect to stem diameter d (m) was determined for a total of 610 species (mosses, n = 40; pteridophytes, n = 16; dicotyledonous herbs, n = 117; palms, n = 17; gymnosperms, n = 105; dicotyledonous trees, n = 315); axial length or mass vs. d was determined for the pteridophyte Psilotum nudum ; and the scaling of critical buckling height hCritof gymnosperm and dicotyledonous trees was calculated based on the record trunk d and average Young’s modulus E and density p of 33 wood species. The scaling exponents (based on least squares and reduced major axis regressions; and αRMA, respectively) of these relations were compared to expected values for three scaling models: elastic similarity, a = 0.666; stress similarity, a = 0.500; and geometric similarity, a = 1.00. Least squares regression of the data from all species yielded h = 22 d0.91(r2= 0-955, n= 610; αRMA= 0.93). The scaling exponent of this formula complied best with the geometric similarity model (a ta 1.00). However, a differed among plant clades and anatomical grades: mosses, = M0 (r2= 0.974; αRMA= 1.12); pteridophytes, aIJ3= 1.69 (r2= 0-S47; αRMA= 1.&3); herbaceous dicotyledons, αLS= 1.26 (r2= 0.742; αRMA= 1.46); palms, αLS= 1.76 (r2= 0-940; αRMA= 1.82); gymnosperm trees, = 0-430 (r = 0.247; αRMA= 0-87); dicotyledonous trees, aLS= 0-488 (r2= 0-515; αRMA= 0-69); woody species (gymnosperm and dicotyledonous trees), = 0-538 (r2= 0-541 ; αRMA= 0.73) ; and non-woody species, αLS= 1.29 (r2= 0-949; αRMA= 1.32). Based on αRMA, the interspecific scaling of woody species complied neither with the stress or elastic similarity model. Regrsession of hCrityielded the formula herit= 97.7 <70 6SB(r2= 0-969; αRMA= 0.70), which was interpreted to support the assumption that Ejp a; a constant among gymnosperm and dicotyledonous woods. Intra- and interspecific variations in αRMAcaution against using any of the three scaling models to predict h based on d across a broad taxonomic spectrum of species, although, on the average, αRMA< 1.0 and αRMA> 1.0 for woody and non-woody species, respectively. © 1993 Annals of Botany Company.