INTRASPECIFIC COMPETITION IN IRRIGATED AND FERTILIZED EUCALYPT PLANTATIONS

A field experiment to study the biomass production of Eucalyptus globulus under different irrigation and fertilization regimes was established in March 1986 in central-west Portugal. In this paper the start of competition under different availability of water and nutrients was analyzed through its consequences both at the individual and stand level. Individual-tree size frequency distribution and size variability, the relationship between mean annual relative growth rate and social status of the tree and percentage of survival were examined in each treatment. It was found that the start of asymmetric competition was strongly influenced by irrigation and fertilization as it occurred by the time of canopy closure, about 2.8 years and 4.8 years of age, respectively, in the irrigated and fertilized plots and in the control plots. Although at that time none of the plots had begun to suffer density-dependent mortality, severe suppression of smaller trees by the dominants (therefore asymmetric competition) was observed in all plots. Asymmetric competition was also detected by an increase in size variability occurring also at the time of canopy closure.