Gabrielle Vivian-Smith

Lantana (Lantana camara) Seed Bank Dynamics: Seedling Emergence and Seed Survival

Abstract Seed persistence is poorly quantified for invasive plants of subtropical and tropical environments and Lantana camara, one of the worlds worst weeds, is no exception. We investigated germination, seedling emergence, and seed survival of two lantana biotypes (Pink and pink-edged red [PER]) in southeastern Queensland, Australia. Controlled experiments were undertaken in 2002 and repeated in 2004, with treatments comprising two differing environmental regimes (irrigated and natural rainfall) and sowing depths (0 and 2 cm). Seed survival and seedling emergence were significantly affected by all factors (time, biotype, environment, sowing depth, and cohort) (P < 0.001). Seed dormancy varied with treatment (environment, sowing depth, biotype, and cohort) (P < 0.001), but declined rapidly after 6 mo. Significant differential responses by the two biotypes to sowing depth and environment were detected for both seed survival and seedling emergence (P < 0.001). Seed mass was consistently lower in the PER biotype at the population level (P < 0.001), but this variation did not adequately explain the differential responses. Moreover, under natural rainfall the magnitude of the biotype effect was unlikely to result in ecologically significant differences. Seed survival after 36 mo under natural rainfall ranged from 6.8 to 21.3%. Best fit regression analysis of the decline in seed survival over time yielded a five-parameter exponential decay model with a lower asymptote approaching −0.38 (% seed survival  =  [( 55 − (−0.38)) · e (k · t)] + −0.38; R2  =  88.5%; 9 df). Environmental conditions and burial affected the slope parameter or k value significantly (P < 0.01). Seed survival projections from the model were greatest for buried seeds under natural rainfall (11 yr) and least under irrigation (3 yr). Experimental data and model projections suggest that lantana has a persistent seed bank and this should be considered in management programs, particularly those aimed at eradication. Nomenclature: Lantana, Lantana camara L.

Reproductive ecology of invasive Ochna serrulata (Ochnaceae) in south-eastern Queensland

We investigated aspects of the reproductive ecology of Ochna serrulata (Hochst.) Walp., an invasive plant in eastern Australia. O. serrulata drupes were similar in size to fleshy fruits of other local invasive plants, but showed some distinct differences in quality, with a very high pulp lipid content (32.8% of dry weight), and little sugar and water. Seeds were dispersed by figbirds, Sphecotheres viridis Vieillot, a locally abundant frugivore, and comprised between 10 and 50% of all non-Ficus spp. fruit consumed during October and November. The rate of removal of O. serrulata drupes was greater in bushland than suburban habitats, indicating that control in bushland habitats should be a priority, but also that suburban habitats are likely to act as significant seed sources for reinvasion of bushland. Germination occurred under all seed-processing treatments (with and without pulp, and figbird gut passage), suggesting that although frugivores are important for dispersal, they are not essential for germination. Recruitment of buried and surface-sown seed differed between greenhouse and field experiments, with minimal recruitment of surface-sown seed in the field. Seed persistence was low, particularly under field conditions, with 0.75% seed viability after 6 months and 0% at 12 months. This provides an opportunity to target control efforts in south-eastern Queensland in spring before fruit set, when there is predicted to be few viable seeds in the soil.

Comparative Seed and Dispersal Ecology of Three Exotic Subtropical Asparagus Species

Abstract The genus Asparagus includes at least six invasive species in Australia. Asparagus aethiopicus and A. africanus are invasive in subtropical Australia, and a third species, A. virgatus is naturalized and demonstrates localized spread in south east Queensland. To better understand how the attributes of these species contribute to their invasiveness, we compared fruit and seed traits, germination, seedling emergence, seed survival, and time-to-maturity. We further investigated dispersal ecology of A. africanus, examining the diet of a local frugivore, the figbird (Sphecotheres viridis) and the effect of gut passage on seedling emergence. Overall, A. aethiopicus was superior in germination and emergence, with the highest mean germination (98.8%) and emergence (94.5%) under optimal conditions and higher emergence (mean of 73.3%) across all treatments. In contrast, A. africanus had the lowest germination under optimal conditions (71.7%) and low mean seedling emergence (49.5%), but had fruits with the highest relative yield (ratio of dry pulp to fruit fresh weight) that were favored by a local frugivore. Figbirds consumed large numbers of A. africanus fruits (∼30% of all non-Ficus fruits), and seedling germination was not significantly affected by gut passage compared to unprocessed fruits. Asparagus virgatus germinated poorly under cool, light conditions (1.4%) despite a high optimum mean (95.0%) and had low mean performance across emergence treatments (36.3%). The species also had fruits with a low pulp return for frugivores. For all species, seed survival declined rapidly in the first 12 mo and fell to < 3.2% viability at 36 mo. On the basis of the traits considered, A. virgatus is unlikely to have the invasive potential of its congeners. Uniformly short seed survival times suggest that weed managers do not have to contend with a substantial persistent soil-stored seed bank, but frugivore-mediated dispersal beyond existing infestations will present a considerable management challenge. Nomenclature: Basket asparagus, Asparagus aethiopicus L. [syn. Protasparagus aethiopicus (L.) Oberm., Asparagus lanceus Thunb., Asparagus sprengeri Regel, Asparagus densiflorus (Kunth) Jessop]; climbing asparagus, Asparagus africanus Lam. [syn. Protasparagus africanus (Lam.) Oberm]; Asparagus fern, Asparagus virgatus (Baker) Oberm.; figbird, Sphecotheres viridis Viellot.

Seedling recruitment, seed persistence and aspects of dispersal ecology of the invasive moth vine, Araujia sericifera (Asclepiadaceae)

We investigated germination, seedling emergence and seed persistence of the invasive moth vine (Araujia sericifera Brot.) under controlled and field conditions in south-eastern Queensland. Fresh seed showed high viability (99.5%) and germinated readily, with 97.2% of all recorded germinations occurring within 14 days. Mean germination rates ranged from 74 to 100% across the range of temperature (10/20°C, 15/25°C and 20/30°C alternating 12-h thermoperiods) and light (0- and 12-h photoperiods) treatments. Germination was significantly reduced only under cool, dark conditions. In a 24-month field experiment, seedling emergence was greatest for seeds buried at 1 cm (mean = 96.3%), intermediate for seeds buried at 5 cm (mean = 62.7%) and least for surface-sown seeds (mean = 30.7%). Seed persistence under field conditions was low, declining rapidly to 3.9% at 6 months and to 0.67% at 24 months. Moth vine’s capacity to germinate readily and the rapid depletion of seeds under field conditions indicate that the species has a transient seed bank in south-eastern Queensland. In an additional experiment testing the capacity of seeds for secondary dispersal by water, the mean floating time of seeds was 15.4 days, suggesting that water could act as a secondary dispersal vector, contributing to long-distance dispersal. We recommend that surveillance methods for detecting moth-vine populations should consider both water-flow patterns and wind direction.