What common‐garden experiments tell us about climate responses in plants

Abstract

1. Common garden experiments are indoor or outdoor plantings of species or populations collected from multiple distinct geographic locations, grown together under shared conditions. These experiments examine a range of questions for theory and application using a variety of methods for analysis. The eight papers of this special feature comprise a cross section of contemporary approaches, summarized and synthesized here by what they tell us about the relationships between climate-related trait spectra and fitness optima.2. Four of the eight papers are based on field experiments in prairie, desert, Mediterranean and boreal biomes. Representative of many common garden experiments, these experiments reveal consistent evidence of traits varying with population climate provenance, but evidence of a tradeoff between growth and tolerance traits or of consistent fitness optimization at home is scant, in contrast to trait theory. Two synthesis papers highlight dominant patterns of trait divergence, including for an exotic invasive species. One theoretical paper warned that unknown kinship relationships between populations can result in the misidentification of adaptive trait divergence. A third synthesis paper formulated novel and ambitious goals for common-garden studies through including measurement of response variables at multiple levels of biological organization.3. The featured papers discuss multiple avenues for improving common garden studies. Genomic analysis, together with the quantification of kinship relationships, will continue to reveal the influence of environmental drivers on gene selection. Measuring a more complete set of fitness traits, especially for traits related to regeneration, will permit the development of projection models to explicitly link trait spectra, climate patterns and fitness consequences. More standardized data reporting will additionally improve abilities to synthesize findings across experiments. Testing population performance in competition with other species will produce more robust fitness comparisons between genotypes, especially for slower-growing genotypes in higher-resource environments. Adding gardens in and beyond climatic edge locations will furthermore strengthen the understanding of population failure and species exclusion. Finally, there is unrealized potential in

Forest tree species adaptation to climate across biomes: Building on the legacy of ecological genetics to anticipate responses to climate change

“…Common garden experiments evaluating populations from a species natural range are particularly useful to understand intraspecific variation and quantify both genetic variation and phenotypic plasticity (Schwinning et al, 2022). When grown in these common environments, the association between fitness‐related traits and home environment is interpreted as evidence of genetic adaptation to climate (Davis et al, 2005; Etterson et al, 2016; Kawecki & Ebert, 2004; Lortie & Hierro, 2022; Schwinning et al, 2022), even though neutral evolutionary processes, sometimes related to postglacial recolonization routes, can result in neutral genetic variation associated with environmental gradients (e.g., López‐Goldar et al, 2019). When populations are tested in several common gardens, their phenotypic plasticity can also be quantified (e.g., Schwinning et al, 2022).…”

The role of dominant prairie species ecotypes on plant diversity patterns of restored grasslands across a rainfall gradient in the US Great Plains

“…Species composition was surveyed in a reciprocal common garden experiment after four and 11 years. A reciprocal transplant garden provides a powerful resource to demonstrate the association between phenotypic variation and environmental gradient, local adaptation across regions, and the performance of ecotypes in native and foreign habitats (Johnson et al, 2021; Schwinning et al, 2022). We illustrate our hypotheses schematically (Figure 1).…”

Seed sourcing strategies for ecological restoration under climate change: A review of the current literature

“…Common garden and reciprocal transplant experiments, especially when the maternal identity of propagation materials is maintained throughout the experiment, are the optimal way to test how climate and other environmental conditions interact with the genetic background of individuals and population to affect heritable traits and phenotypic plasticity (Schwinning et al, 2022). Such genecological studies undertaken for tree species have far outpaced those focused upon shorter-lived species (Aitken and Bemmels, 2016).…”