The effect of Phytophthora cinnamomi on basal area increment of natural stands of Eucalyptus sieberi.  W.D. Incoll and P.C. Fagg.  October 1973.  11 pp. (unpubl.)

SUMMARY

This study examined the effects of infection by Phytophthora cinnamomi on the periodic gross increment of basal area (GBAI) of Eucalyptus sieberi. The study involved well-stocked stands on well-drained foothills near Orbost and Moe in east Victoria.

Seventeen temporary sample plots, each 0.05 acre in area, were used. For each plot a measure of the “infection intensity” of P. cinnamomi was obtained as follows: Soil samples were taken at the intersections of a 10 ft. x 10 ft. grid, and the percentages of the 25 soil samples per plot that were positive for P. cinnamomi was calculated.

For each plot the actual GBAI (two year period) was estimated from increment cores. An estimate of GBAI for the plot was also made using a growth model derived for uninfected stands. The difference between actual GBAI and “infection-free” GBAI was then related to infection intensity.

The results indicated that infection intensity was not related to the difference between the two estimates of GBAI. Thus it could be said at least for the case studied (well-stocked stands on well-drained foothills), that the growth model estimated GBAI without significant bias, regardless of infection intensity. This does not prove that P. cinnamomi did not reduce GBAI in the infected stands, because if the infection had been of long standing it might have affected the estimates of the stand parameters (age, site index and basal area per acre) used in the growth model, in which case biased estimates of “infection-free” GBAI might result. However, further examination of this problem strongly suggested that this source of error was unimportant. It was therefore concluded that infection with P. cinnamomi in fact had little or no effect on GBAI.

Further studies are required to determine how general this conclusion might be.

Also published:

Incoll, W.D. and Fagg, P.C. (1975)  The effect of soil infestation by Phytophthora cinnamomi Rands on basal area growth of Eucalyptus sieberi L. Johnson.  Aust. For. 38 (2): 87-91.