Phenology of Eucalyptus marginata on Sites Infested With Phytophthora cinnamomi

Abstract

The phenology of Eucalyptus marginata (jarrah) was followed at three sites, Churchmans, Karnet and Ross, in the high rainfall zone of the jarrah forest for a minimum of 3 years. On each site, trees growing in an area infested with the soil-borne, pathogenic fungus Phytophthora cinnamomi (dieback area) were compared with trees of similar diameter in the adjacent, uninfested forest (healthy area).

Phenology of jarrah on these dieback sites did not follow a consistent pattern. In the dieback area at Churchmans, the cambium was active more often, and trees had young leaves in their crown more frequently than trees in the healthy area, while at Karnet the reverse occurred. This is consistent with growth measurements. At Ross, in the dieback area, the cambium was active less often but young leaves were seen more frequently than in trees in the healthy area.

The trees did not flower every year. At Ross flowering started in early October while at Karnet and Churchmans it started at least 1 month later. New leaves were produced intermittently during autumn and winter while the main leaf flush occurred in spring and summer. Data from all years showed that the leaf flush started earlier at Ross than at Karnet and Churchmans. The cambium was intermittently active throughout the year with most trees growing in late autumn, winter and spring.

Observations of stem growth following unseasonable summer rainfall suggest that cambial activity is triggered by high, surface soil moisture, but only if soil aeration is adequate. It is unlikely that timing of the main leaf flush and flowering are determined solely by temperature, soil moisture or photoperiod.