Relations between reproductive growth and vegetative growth of Pinus radiata

Abstract

Growth of female cones and male cones of Pinus radiata was measured and compared with vegetative growth in 10- to 14-year-old plantations given a range of water and nutrient supplies on a site near Canberra, Australia. Although P. radiata trees take about 3 years from ‘flower’ initiation to seed maturation, most of the growth in dry weight occurred in two relatively brief periods: male cones grew mainly in the 3 months before shedding their pollen; female cones grew mainly during the 4 months starting about 13 months after the time of pollen shed. As both male cones and foliage fascicles originate as short-shoot initials, each male cone is produced at the expense of one fascicle of foliage. The number of short-shoots produced was positively related to rainfall during their initiation: about September to January. When this period was dry, fewer short-shoots were initiated and a much lower proportion of these was devoted to male cones. The flowering shoots did not compensate for their loss of fascicles by producing more short-shoots or by growing larger needles. On average, about 13% of the potential foliage was diverted to the production of male flowers. Because female cones originate as long-shoot buds (i.e. buds which otherwise would produce branches), they are also produced at some cost in foliage. Reproductive growth also entailed considerable nutrient cost. Even so, there was no evidence that increased reproductive growth caused any decrease in vegetative growth. Within a stand, stem growth per tree during and shortly after the main growth of male cones did not vary with the abundance of male cones on those trees. The weight of matured male and female cones produced by all five treatments from the four flowerings of 1984–1987 averaged 1.1 t ha −1 year −1. This amount was equal to about 10% of stem growth or 5%% of total above-ground growth. The production of both male and female cones was positively related to rainfall during the September to January period in which the male cones were initiated and also to the vegetative growth that occurred during the year of flower initiation.