The ornamental tree Cascabela thevetia (L.) Lippold has naturalised and formed large infestations at several locations in northern Australia. To better understand its ecology and invasiveness, a field experiment in North Queensland quantified the growth, time to seed formation and survival of seedlings of the peach biotype of C. thevetia growing under two levels of canopy cover (light and dense) within a riparian habitat. Measurements were undertaken 0, 14, 83, 147, 432, 692, 840, 1064, 1204 and 1558 days after new seedlings were tagged in respective treatments.
In the light cover treatment, C. thevetia plant height and basal diameter averaged 275 cm and 39 mm after 1558 days, respectively, compared with 68 cm and 8 mm, respectively, in the dense cover treatment. The quickest time to seed formation occurred in the light cover treatment (between 432 and 692 days), with no seeds recorded in the dense cover treatment after 1558 days. Seedling survival was 83% under light cover compared with 51% under dense cover, at the end of the experiment.
This study has shown how the growth, reproduction and survival of young C. thevetia plants will vary in the landscape. Growth will be most rapid if seedlings are located away from, or on the edge of infestations. Within infestations, seedlings will be constrained by parent plants. The findings also suggest that land managers have a reasonable period (at least 12 months) to detect new plants in susceptible areas (such as riparian habitats) or control seedling regrowth following control programs, before plants could set seed and replenish soil seed banks.
Cite this article as:
Bebawi, F.F., Campbell, S.D. and Mayer, R.J. (2015). The growth, reproduction and survival of Cascabela thevetia seedlings under two levels of canopy cover. Plant Protection Quaterly, 30(1), 21-26.