Seed Ecology of the Invasive Tropical Tree Parkinsonia aculeata

Parkinsonia aculeata is an invasive tree native to tropical America, but introduced to Australia. Propagation and stand regeneration is mainly by seed. To gain baseline knowledge for management decisions, seed bank dynamics were monitored for two months during the fruit dispersal period at a coastal wetland in Costa Rica (native habitat), and at a coastal wetland and two semi-arid rangeland sites in Northern Queensland, Australia (introduced habitats). Seed bank densities underneath dense, uniform Parkinsonia stands were found to be lowest in the Australian wetland but highest in the Costa Rican wetland. Post-dispersal seed losses were highest in the Australian wetland, primarily due to seed germination and/or death. At the other sites, seed losses were minor during the study period, and predation was the most important cause of losses. At the two rangeland sites bruchid beetles accounted for more than 95% of the seed losses by predation. Total predation was lowest in the Costa Rican wetland. In order to test for intrinsic differences of seed characteristics, germination trials were conducted using both canopy seeds and seeds from the soil seed bank. Dormancy release and germination rate were studied under four temperature treatments. In all populations, dormancy release increased with increasing temperature, but averaged responses were significantly different between Costa Rican and Australian seed populations, and between seeds collected from the soil and from trees. Germination rate of scarified seeds was fastest at 35°C in all tested seed populations. While high seed germination levels seem to explain low seed bank densities in the Australian wetland, the large seed banks at the rangeland sites reflect the lower incidence of favourable conditions for germination. In the Australian wetland biocontrol with bruchids is unlikely to be successful, while control by conventional methods, such as killing stands by basal bark spraying, seems feasible, due to a lower long-term risk of re-infestation from the soil seed bank. At the rangeland sites conventional control will be difficult and costly. Parkinsonia stands may be better left to their own, while bruchid populations are monitored and management efforts are concentrated on preventing further invasio

Pollination processes in Idiospermum australiense (Calycanthaceae), an arborescent basal angiosperm of Australia's tropical rain forests

Idiospermum australiense (Diels) S.T. Blake, a rainforest canopy tree restricted to a few small populations in northeast Australia, is the only southern hemisphere representative of the Calycanthaceae. Pollination processes in Idiospermum were investigated. Flowers are protogynous, with some populations of the species being andromonoecious, whilst others are hermaphrodite. Over their 10 – 16 day floral lifespan, movements of floral organs enforced spatial and temporal separation of male and female floral function. Changes in colour and intensity of fragrance may also influence their attractiveness to potential pollinators. Pollen is present in large quantities, and appears to act as a reward for floral visitors. Insect trapping was carried out both within flowers, and immediately adjacent to inflorescences. A wide variety of arthropods was trapped, with thrips being the most abundant. Other arthropods were trapped, including fourteen species of beetle. For arthropods other than thrips, the mean numbers of adults trapped on flowers remained more or less constant throughout the floral lifetime. However, there was a significant interaction between floral age and the number of pre-adult arthropods present – as the flower aged, the mean number of larvae and eggs per flower increased. The flowers appear to act as sheltered mating and brooding sites for small insects

Figuring out the figs: the Ficus obliqua - Ficus rubiginosa complex (Moraceae: Urostigma sect. Malvanthera)

A revision of the Ficus obliqua—F. rubiginosa complex (Moraceae: Urostigma sect. Malvanthera Corner) is presented. A phenetic analysis of morphometric characters using clustering techniques and multidimensional scaling was used to identify the taxa in this complex. Three taxa are recognised, F. obliqua G.Forst., F. rubiginosa Desf. ex Vent. f. rubiginosa and F. rubiginosa f. glabrescens (F.M.Bailey) D.J.Dixon. Each taxon is redescribed. The epithet glabrescens of F. rubiginosa f. glabrescens is resurrected with a change in status. The data from the pollinator wasps strongly supports the taxonomy, with F. obliqua pollinated by Pleistodontes greenwoodi (Grandi) and F. rubiginosa sens lat. pollinated by P. imperialis Saunders. A key to the species and infraspecific taxa of F. rubiginosa as well as notes and distribution maps are provided for both species

Isozyme markers in Saccharum spp. hybrids and Erianthus arundinaceus (Retz.) Jeswiet

Verification of the authenticity of the hybrid origin of progeny from interspecific or intergeneric crossing in introgression studies in plant improvement is essential before usage of such progeny. This study undertook to determine whether isozyme phenotypes verified the hybrid origin of apparent crosses between a clone of Erianthus arundinaceus (Retz.) Jeswiet and several Saccharum spp. hybrid clones. Starch gel electrophoresis was used to resolve 18 isozyme systems for markers that would distinguish E. arundinaceus from Saccharum spp. hybrid clones. Eight isozyme systems revealed 16 bands that were present in E. arundinaceus but absent from the sugarcane parents. When a population of putative E. arundinaceus × Saccharum spp. hybrid progeny was screened using these isozyme systems, none of the clones expressed the bands characteristic of E. arundinaceus. Thus, their intergeneric nature was disproven

Seed ecology of the invasive tropical tree Parkinsonia aculeata

Parkinsonia aculeata is an invasive tree native to tropical America, but introduced to Australia. Propagation and stand regeneration is mainly by seed. To gain baseline knowledge for management decisions, seed bank dynamics were monitored for two months during the fruit dispersal period at a coastal wetland in Costa Rica (native habitat), and at a coastal wetland and two semi-arid rangeland sites in Northern Queensland, Australia (introduced habitats). Seed bank densities underneath dense, uniform Parkinsonia stands were found to be lowest in the Australian wetland but highest in the Costa Rican wetland. Post-dispersal seed losses were highest in the Australian wetland, primarily due to seed germination and/or death. At the other sites, seed losses were minor during the study period, and predation was the most important cause of losses. At the two rangeland sites bruchid beetles accounted for more than 95% of the seed losses by predation. Total predation was lowest in the Costa Rican wetland. In order to test for intrinsic differences of seed characteristics, germination trials were conducted using both canopy seeds and seeds from the soil seed bank. Dormancy release and germination rate were studied under four temperature treatments. In all populations, dormancy release increased with increasing temperature, but averaged responses were significantly different between Costa Rican and Australian seed populations, and between seeds collected from the soil and from trees. Germination rate of scarified seeds was fastest at 35°C in all tested seed populations. While high seed germination levels seem to explain low seed bank densities in the Australian wetland, the large seed banks at the rangeland sites reflect the lower incidence of favourable conditions for germination. In the Australian wetland biocontrol with bruchids is unlikely to be successful, while control by conventional methods, such as killing stands by basal bark spraying, seems feasible, due to a lower long-term risk of re-infestation from the soil seed bank. At the rangeland sites conventional control will be difficult and costly. Parkinsonia stands may be better left to their own, while bruchid populations are monitored and management efforts are concentrated on preventing further invasion