The response of Eucalyptus obliqua regrowth to release in irregular stands of mixed eucalypts in west-central Victoria. R.O. Squire and J.G. Edgar.  June 1975.  22 pp. (unpubl.)

SUMMARY

Preliminary results are presented of a study established in 1970 to test the growth responses of individual regrowth stems of Eucalyptus obliqua (messmate) growing in irregular stands of mixed species of eucalypts, in the Wombat State Forest.

Growth responses during the period 1970-73 are investigated by examination of gross periodic basal area increment (BAI) and crown activity (an index of potential for height growth following release). Stems were examined within each of six initial competition classes and five diameter classes. Four release treatments, covering the range from zero to near complete removal of competition, were applied to stems within each of the 30 stem size:competition classes.

Graphical techniques have been used to examine the relationships between growth responses and measures of stem diameter (DBHOB), density of competing stems and crown position (dominance class), which were taken at the time of stem release (1970).

Results showed that heavy release treatments have produced high BAI on individual stems for all diameters studied (0-12 in - 0 to about 30.5 cm). For most diameters (2 to 8 in - about 5 to 20 cm), BAI of heavily released stems is at least double that of unreleased stems of the same diameter.

In linear regression models of BAI on pre-release diameter, 71.3% of the variation in BAI is accounted for by the measure of diameter. By contrast, only a small amount of variation in BAI is explained by regressions of BAI on pre-release density of competition or on crown position.

If BAI is measured in relative terms as a percentage of initial stem basal area, the results indicate that stems in all of the pre-release combinations of diameter, density and crown position classes which were examined, have a high capacity to respond to release treatments.

Crown activity is also stimulated by release. Stems of all crown classes possess reasonable potential for active crown development following release.

Taken together, the BAI and crown activity responses indicate that regrow stems from a broad range of diameter, density of competition and crown position classes are of crop tree potential. Such results indicate a clear opportunity for economic gain by exploiting the potential of existing regrowth for accelerated development. Such actions will reduce the production time for specific forms of final crop trees and thereby potentially improve both the economics of production and the flow of products. The ability to respond also represents an inherent flexibility which can be used to advantage in coping with less material objectives of forest stand management.