Seed banks of native forbs, but not exotic grasses, increase during extreme drought

Extreme droughts such as the one that affected California in 2012-2015 have been linked to severe ecological consequences in perennial-dominated communities such as forests. In annual communities, drought impacts are difficult to assess because many species persist through facultative multiyear seed dormancy, which leads to the development of seed banks. Impacts of extreme drought on the abundance and composition of the seed banks of whole communities are little known. In 80 heterogeneous grassland plots where cover is dominated by ~15 species of exotic annual grasses and diversity is dominated by ~70 species of native annual forbs, we grew out seeds from soil cores collected early in the California drought (2012) and later in the multiyear drought (2014), and analyzed drought-associated changes in the seed bank. Over the course of the study we identified more than 22,000 seedlings to species. We found that seeds of exotic annual grasses declined sharply in abundance during the drought while seeds of native annual forbs increased, a pattern that resembled but was even stronger than the changes in aboveground cover of these groups. Consistent with the expectation that low specific leaf area (SLA) is an indicator of drought tolerance, we found that the community-weighted mean SLA of annual forbs declined both in the seed bank and in the aboveground community, as low-SLA forbs increased disproportionately. In this system, seed dormancy reinforces the indirect benefits of extreme drought to the native forb community.

Livestock in no-till cropping systems - a story of trade-offs

The trade-offs of incorporating livestock into no-till cropping systems were examined with respect to ground cover, water balance, nutrient cycling, pest management, whole-farm economics and farmer preferences. The hypothesis that livestock and no-till cropping enterprises may co-exist was investigated using a review of scientific literature and technical reports, information from farmer focus groups and an economic analysis based on case study data from farm consultants. The scientific review focussed on work from Australia, especially western and southern Australia, but also included research related to systems in northern New South Wales and southern Queensland and some related international work. The focus groups and case studies were from the cereal-sheep systems of western and southern Australia. It was concluded that the use of livestock in a no-till system is determined by the productive capacity of the land, the relative profitability of cropping and livestock, the management of herbicide-resistant weeds, sensitivity of soil to damage from grazing and trampling and the farmer’s passion, preference and willingness to apply increased management to livestock. Livestock are an important source of farm diversification and risk management. While net farm income tends to decline as the proportion of livestock increases, variation in net farm income also decreases, reducing volatility in revenue. Livestock need to comprise above 10–15% of net farm income to provide a positive impact on variability of return. Adaptation of mixed-farming systems through rotational grazing, temporary agistment of livestock or removal to non-cropping areas are all management options that may be utilised to remove or reduce potential negative impacts, improve integration and to realise triple-bottom-line gains.