The eco-evolutionary risks of not changing seed provenancing practices in changing environments

Sourcing seed from local populations has been the long-standing default for native restoration plantings for numerous eco-evolutionary reasons. However, rapidly changing environments are revealing risks associated with both non-local and local provenancing. As alternative strategies gain interest, we argue to progress seed sourcing discussions towards developing risk-based decision-making that weighs the risks of changing and not changing in a changing environment, transcending historic default positions and local versus non-local debates.

How well do revegetation plantings capture genetic diversity?

Revegetation plantings are a key management tool for ecological restoration. Revegetation success is usually measured using ecological traits, however, genetic diversity should also be considered as it can influence fitness, adaptive capacity and long-term viability of revegetation plantings and ecosystem functioning. Here we review the global literature comparing genetic diversity in revegetation plantings to natural stands. Findings from 48 studies suggest variable genetic outcomes of revegetation, with 46% demonstrating higher genetic diversity in revegetation than natural stands and 52% demonstrating lower diversity. Levels of genetic diversity were most strongly associated with the number of source sites used-where information was available, 69% of studies showing higher genetic diversity in revegetation reported using multiple provenances, compared with only 33% for those with lower diversity. However, with a few exceptions, it was unclear whether differences in genetic diversity between revegetation and natural stands were statistically significant. This reflected insufficient reporting of statistical error and metadata within the published studies, which limited conclusions about factors contributing to patterns. Nonetheless, our findings indicate that mixed seed sourcing can contribute to higher genetic diversity in revegetation. Finally, we emphasize the type of metadata needed to determine factors influencing genetic diversity in revegetation and inform restoration efforts.

Plant community response to switchgrass (Panicum virgatum) population source in establishing prairies

Ecological restoration and revegetation efforts entail the translocation of native plant populations. Risks associated with these efforts include failure of translocated populations to establish or, conversely, such strong establishment that they excessively dominate the recipient community. The role that selective breeding plays in mediating these risks is unclear but of increasing importance as efforts to restore and establish multifunctional grasslands also increase. In a three-year, spatially replicated study, we seeded experimental prairie communities with either domesticated (cultivar) or undomesticated strains of Panicum virgatum (switchgrass), a North American C₄ species under development as a biomass crop. We evaluated the composition, performance, and diversity of the recipient plant communities and compared the performance of cultivar and undomesticated switchgrass in those communities. We found little evidence that switchgrass population source affected community response. Switchgrass cultivars modestly exceeded undomesticated strains with respect to stand establishment, third-year stand density, and aboveground biomass; effect size and significance differed among sites. Our results suggest that including cultivars in ecological restorations and multifunctional grasslands may enhance success of switchgrass establishment with little risk of impairing the composition or diversity of plant communities for up to three years, as reflected in the measures used here. However, the incorporation of undomesticated switchgrass into multifunctional grasslands may enhance landscape-scale genetic variation and mitigate risks associated with gene flow between translocated and local wild switchgrass populations; more research on these dynamics is needed.

Extensive variation, but not local adaptation in an Australian alpine daisy

Alpine plants often occupy diverse habitats within a similar elevation range, but most research on local adaptation in these plants has focused on elevation gradients. In testing for habitat‐related local adaptation, local effects on seed quality and initial plant growth should be considered in designs that encompass multiple populations and habitats. We tested for local adaptation across alpine habitats in a morphologically variable daisy species, Brachyscome decipiens, in the Bogong High Plains in Victoria, Australia. We collected seed from different habitats, controlled for maternal effects through initial seed size estimates, and characterized seedling survival and growth in a field transplant experiment. We found little evidence for local adaptation for survival or plant size, based on three adaptation measures: Home versus Away, Local versus Foreign, and Sympatric versus Allopatric (SA). The SA measure controlled for planting site and population (site‐of‐origin) effects. There were significant differences due to site‐of‐origin and planting site effects. An important confounding factor was the size of plants directly after transplantation of seedlings, which had a large impact on subsequent seedling survival and growth. Initial differences in plant width and height influenced subsequent survival across the growing season but in opposing directions: wide plants had higher survival, but tall plants had lower survival. In an additional controlled garden experiment at Cranbourne Royal Botanic Gardens, site‐of‐origin effects detected in the field experiments disappeared under more benign homogeneous conditions. Although B. decipiens from different source areas varied significantly when grown across a range of alpine habitats, these differences did not translate into a local or habitat‐related fitness advantage. This lack of local advantage may signal weak past selection, and/or weak adaptive transgeneration (plasticity) effects.