© 1990 Heron Publishing—Victoria, Canada
Influence of male and female cones on assimilate production of Pinus contorta trees within a forest stand
Janet McP. Dick (1), Paul G. Jarvis (2) and Craig V. M. Barton (2)
1. Institute of Terrestrial Ecology, Bush Estate, Penicuik, Midlothian, EH26 0QB, Scotland / 2. Institute of Ecology and Resource Management, University of Edinburgh, Darwin Building, The King’s Buildings, Mayfield Road,
Edinburgh, EH9 3JU, U.K. /
Summary
Studies on branches of field-grown Pinus contorta Dougl. trees showed that: (i) branches with fully developed male or female cones were heavier than vegetative branches; (ii)
the production of female cones decreased neither the number of laterals nor the length of the terminal or lateral shoots on
the cone-bearing branches; (iii) the production of male cones decreased both the number of laterals and the number of needles
on the cone-bearing branches; (iv) needles on male cone-bearing branches had significantly higher photosynthetic rates and
needles on female cone-bearing branches generally also fixed more CO2 per quantum of light. In addition, both male and female cones refixed a significant proportion of respired CO2 when illuminated.
The simulation model, MAESTRO, was used to estimate light penetration through two stands (3690 and 1845 trees ha–1) of P. contorta trees and to calculate the resultant CO2 assimilation of a vegetative, a male and a female cone-bearing tree on sunny, partly sunny and cloudy days in Scotland. Generally,
the CO2 efflux from female cones was less than 3% of the CO2 assimilated by the whole tree. The presence of male cones resulted in an average 33% decrease in needle complement, but an
increased quantum efficiency of associated needles in the autumn. It was estimated that, on a sunny day, male
cone-bearing trees assimilated as much CO2 as vegetative trees in the high density stand and only 6% less in the low density stand. On cloudy days, the smaller needle
complement was beneficial to the carbon economy of the tree because of lower respiration losses compared with a vegetative
tree.
