Regrowth of Cassinia rugata
Cassinia rugata is our top priority threatened plant species. Plants appear to dislike shading and tend to become leggy and senescent over time in their preferred open habitat.
Many of the Cassinia rugata shrubs at Rubicon were burnt in an ecological burn of Wet Heathland (SHW) on 4 April 2013. These shrubs, and others at Rubicon, had previously regenerated from a burn in 2007 at the property, but we knew little about the process of regeneration. The purpose of this experiment is to monitor the process of regeneration, and to determine whether caging of re-sprouting plants is beneficial.
Following a burn, many plants re-sprout from the base, but the regrowth tends to be heavily grazed when plants are unprotected.
In total, 204 burnt plants were identified by June 2013. Within one of the burn units, we randomly selected for monitoring 10 of the 13 apparently dead plants and 20 of the 120 re-sprouting plants, with an alternate allocation to caged and uncaged treatments. Plants were labeled with flags and cages were installed on 10 June 2013.
By October 2013 four of the 10 apparently dead plants had re-sprouted: three caged plants and one uncaged plant. By this stage there was a stark grazing effect: the maximum stem height for caged plants was 114.4mm compared with 55.5mm for uncaged plants.
The plants have been monitored twice a year since then. After the 2014-15 growing season, in February 2015, one of the robust caged plants was flowering as if it hadn't been burnt.
By February 2016, we find that caging has no significant effect on plant mortality. Median heights for living caged and uncaged plants are 855 mm and 270 mm respectively, and the distributions of the two groups of plant heights differ very significantly. Eight of the caged plants but only one uncaged plant flowered, mostly for the second consecutive year. With respect to the original population of living caged and uncaged plants, this is significant difference. In summary, cages apparently protect plants from grazing, and the caged plants are able to recover more quickly from the burn and start to flower sooner than caged plants.