© 2007 Heron Publishing—Victoria, Canada
Maximum plant height and the biophysical factors that limit it
Karl J. Niklas
Department of Plant Biology, Cornell University, Ithaca, NY 14853, USA (kjn2 @ cornell.edu) / Received October 3, 2005; accepted December 4, 2005; published online December 1, 2005
Summary
Basic engineering theory and empirically determined allometric relationships for the biomass partitioning patterns of extant
tree-sized plants show that the mechanical requirements for vertical growth do not impose intrinsic limits on the maximum
heights that can be reached by species with woody, self-supporting stems. This implies that maximum tree height is constrained
by other factors, among which hydraulic constraints are plausible. A review of the available information on scaling relationships
observed for large tree-sized plants, nevertheless, indicates that mechanical and hydraulic requirements impose dual restraints
on plant height and thus, may play equally (but differentially) important roles during the growth of arborescent, large-sized
species. It may be the case that adaptations to mechanical and hydraulic phenomena have optimized growth, survival and reproductive
success rather than longevity and mature size.
Keywords:
allometry, biomechanics, hydraulic constraints, maximum height, plant evolution, power rules.
