The effect of seedtrees on regrowth development in a mixed-species eucalypt forest

Previous studies have shown that the retention of overwood can have suppressive effects on the development of regrowth. In this study we compared the effect of retaining seed trees (mature Eucalyptus pilularis), and removing seed trees, on the regrowth of E. pilularis and the more tolerant eucalypt species such as E. microcorys, E. propinqua, E. acmenoides, and E. paniculata. The study utilised a mixed hardwood stand located within Pine Creek State Forest, near Coffs Harbour in north-eastern New South Wales. The stand had been regenerated in 1972 leaving 15 seed trees/ha. Half of the seed trees were removed in 1990. Measurements of height, diameter, and distance of regrowth trees to the seed trees indicated that the height of regrowth was significantly affected by distance from seed tree (removed or retained). This suppressive effect was significantly more pronounced for E. pilularis than for more tolerant species. Height development of the regrowth improved significantly where seed trees had been removed. For the intolerant species the height-to-diameter ratio decreased with distance from seed tree (removed or retained), whereas for tolerant species the height to diameter ratio remained constant over all distances. The results of this study confirm that intolerant eucalypt species are more sensitive to overstorey competition than more tolerant species, and that the relative loss of production from the retention of mature trees may be smaller in mixed stands consisting of tolerant and intolerant eucalypt species than in mono-specific stands of intolerant species