Caladenia congesta caging experiment
Caladenia congesta, the blacktongue finger-orchid, occurs in Tasmania, Victoria, South Australia, ACT and New South Wales. Its conservation status is rare in South Australia and endangered in Tasmania, where it has only been recorded from four sites in the past 20 years. Existing records are generally for a few individual plants in localised areas of heathy woodland and open forest (Threatened Species Section 2012).
The population of about 30 plants at Rubicon grows at one site in dry to damp Eucalyptus amygdalina coastal forest and woodland (DAC).
We have settled on a pattern of management for the small area where Caladenia congesta is known to grow at Rubicon. We slash the area every third autumn. The typical response from the plants is that flowering reaches a maximum during the second spring after the slash and then declines in the third spring. Because emerging orchid plants are especially vulnerable to being grazed after the slashing, over the years we have randomly allocated of half of the known plants to be protected from herbivores by a wire-netting cage.
Results in previous years had found that caging of plants was worthwhile only during the year immediately after disturbance. The area occupied by the Caladenia congesta population was slashed in autumn 2015. However, in spring 2015, there was no significant difference in leaf emergence or flowering between the 15 caged plants and 14 uncaged plants.