© 1990 Heron Publishing—Victoria, Canada
Theoretical study of variables affecting the export of assimilates from branches of Picea
M. G. R. Cannell (1) and J. Morgan (2)
1. Institute of Terrestrial Ecology, Bush Estate, Penicuik, Midlothian EH26 0QB, Scotland / 2. Department of Civil Engineering, University of Edinburgh, King’s Buildings, Edinburgh EH9 3SU, Scotland / Received November 20, 1989
Summary
A theoretical analysis was done to identify the features of conifer branch development, based on a model for Picea sitchensis (Bong.) Carr., that affect the ability to export assimilates, assuming (i) a branch’s requirement for assimilates is determined
by its need for mechanical support, and (ii) the production of assimilates is a simple function of total shoot length. There
were three salient findings. First, there is an optimum and maximum shoot length for assimilate export by unbranched shoots.
Second, the less a shoot extends itself each year, the more assimilate it may export, all else being equal. Third, there is
a larger surplus of assimilates for export when a shoot develops laterals. A combination of lateral branching, deflection
and decreased elongation can enable branches to continue growing and exporting assimilates for many years, as occurs at the
bases of tree crowns.
