Effect of overwood trees on growth of young stands of Eucalyptus sieberi

Summary The suppressive effect of overwood trees on regrowth was studied by establishing transects from isolated overwood trees into established 20 to 30 year-old regrowth. Plots three metres in diameter were established at five metre intervals along the transects, and the diameter and height of the three regrowth trees of largest diameter on each plot were measured. Basal area was estimated at each plot using “probability proportional to size” (PPS) sampling. The measurements showed that the overwood trees influenced the volume of regrowth on an area of diameter four to six times the diameter of the overwood crowns. The relationship of regrowth volume to distance from single overwood trees was calculated. This relationship was used on hypothetical regrowth stands to estimate the effect on stand volume of a number of overwood trees per hectare. Several hypotheses of the effects in overlapping zones of influence were tested in the course of this synthesis and further field data were collected in an attempt to select the most appropriate hypothesis. An estimate of the loss in standing volume per hectare in the regrowth due to suppression by the overwood was made.