Azadirachta indica (Neem tree) has become widely naturalised and invasive across many countries and regions including northern Australia. To aid management of A. indica where it has become a weed, a series of studies were undertaken to determine its potential soil seed bank persistence. In a field trial, packets of seeds were buried, retrieved periodically over two years and the seed viability assessed. Viability declined rapidly, with a single viable seed retrieved after 12 months burial and none thereafter. Burial depth, soil type, and pasture cover (present and excluded) significantly influenced viability (%) at 3- and 6-month retrievals. Similar data were obtained from repeated runs of a controlled ageing laboratory experiment, which categorized seeds as forming a ‘transient’ seed bank. In a third trial, fresh fruits were placed on the soil surface in replicated field enclosures over two consecutive years and seedling emergence monitored fortnightly. In both years there was no emergence from pasture excluded soil plots and emergence ceased after 2.3 and 8.4 months in plots with pasture present. A fourth (glasshouse) trial found most seeds will emerge from the soil when buried from 1 to 4 cm. However, more fatal germination than successful emergence was recorded for seeds buried at 8 cm. Seed desiccation and fatal germination are factors in A. indica developing a transient soil seed bank, and infestations require shorter-term control programs where seed input is prevented.

Stevia ovata Willd. is an invasive weed that has become naturalised in northern Queensland, Australia. To aid management of current infestations, this study evaluated seed germination under a range of constant (13-48°C) and alternating (11/7 to 52/42°C) temperature regimes and quantified the potential longevity of soil seed banks. The effect of different soil types, levels of pasture cover and burial depths on seed longevity was investigated in both the dry- and wet-tropics of North Queensland. Germination of S. ovata occurred under a wide range of both constant (13-39°C) and alternating day/night temperatures (16/12 to 52/42°C), but optimum conditions ranged between 24 and 27°C and 24/20 and 37/31°C respectively. As temperatures declined below the optimum, an increasing proportion of seeds went into a state of enforced dormancy. In contrast, higher than optimum temperatures caused a proportion of seeds to lose viability. Differential responses in seed longevity of S. ovata occurred between the two experimental sites. In the wet-tropics, seed viability was <1% after 12 months and fully expired after 18 months, irrespective of burial depth. In the dry-tropics, seeds persisted for longer (nil viability after 24–42 months) and burial depth had a significant effect. Surface located seeds tended to exhibit a faster rate of decline in viability than seeds buried below ground. These findings have implications for the duration of control/eradication programs and also suggest that S. ovata has the potential to greatly expand its current distribution, particularly into cooler areas of Australia.

Parthenium hysterophorus L. is highly invasive across many countries, impacting agriculture, human and animal health and the environment. Despite a widespread invasive range, the persistence of P. hysterophorus seeds (achenes) in the soil profile has been identified as a gap in current knowledge. A long-term seed persistence field trial was under-taken, where packets of P. hysterophorus seeds were buried, retrieved periodically over 10 years and the viability assessed. Time, burial depth and soil type (clay or loam) significantly influenced seed viability. Overall viability was <5% after 5 years, and <0.2% of viable seed was recovered after 7 to 10 years. The decline was faster in seeds at 0 cm (on the soil surface) and buried at 20 cm and slower in seeds buried at 2.5 cm and 10 cm. At most retrieval times viability was higher in seeds retrieved from clay soil plots than from loam soil plots. Pasture cover (present or excluded) did not significantly influence the viability of seeds. Data from controlled ageing laboratory experiments indicated persistent seeds and complemented the field trial data. Based on the weight of 1000 seeds, less than 20 mm of rainfall could incorporate 50% of seeds into three soil types. Parthenium hysterophorus develops a persistent seed bank when incorporated into the soil and infestations will require longer-term control even if seed input is prevented.