Restoring dryland ecosystems is challenging, especially when plants must survive hotter, drier, and less predictable conditions. Many restoration tools assume that seeds taken from climates similar to a project site will perform best.
This study put that idea to the test by growing three native plant species from dozens of wild populations in a shared garden. The results showed that no single environmental factor, including climate, soil, or location, explains plant survival on its own. Each species responded differently to temperature, rainfall patterns, soil texture, and even how far the seed had been moved.
During years of extreme heat and drought, only one species benefited from being sourced from similarly harsh climates. The research suggests that relying on one best-matched seed source may be risky, and that using a mix of regionally appropriate sources could better support long-term restoration success.
Research article
Rethinking seed selection based on climate matching during restoration: geographic, soil, and climate variation help explain species-specific mortality patterns
Roybal C.M., Samuel E.M., Mitchell R.M., Winkler D.E., Massatti R.
Impact statement
Restoration professionals often rely on science-based products to help with sourcing plant materials, frequently native seeds, to bolster restoration outcomes. Common products include seed transfer zones, which are geospatial polygons delimiting areas of environmental similarity, and web-based tools that calculate environmental distances between seed sources and restoration sites. These tools are used under the assumption that restoration success is supported when distance between the seed source and restoration site is minimized, an assumption grounded in abundant research on local adaptation.
Analyses of mortality patterns across three plant species, each represented by 10-18 wildland seed sources collected from different environmental distances from an experimental garden, indicate that outcomes vary widely among species when strictly considering climate distance. Many facets of environmental variation influence species, including climate, soils, and unknown aspects correlated with geographic distance. Species also respond to suites of environmental variation uniquely, which makes broad generalizations difficult.
Although a model can be constructed to explain mortality across species, mortality was positively correlated with climate distance for only one species. For each species, the climatically closest population to the experimental garden did not have the lowest mortality. However, averaging mortality rates across seed sources with roughly similar, but not identical, climates always resulted in lower mortality.
The study also assessed mortality in the context of abnormally hot and dry weather at the experimental garden compared to average climates. Predictive provenancing, or tailoring seed sources to current or future weather at a restoration site, worked in retrospect for only one species. These results highlight a potential dryland restoration strategy: if multiple intraspecific, genetically appropriate, and climatically approximate seed sources are available, regional admixture provenancing may increase the probability that plants can establish and persist.
Abstract
Implicit in the construction of seed transfer zones is the assumption that plant populations are adapted to their home climate and that transferring native seed to different climatic areas risks maladaptation and poor plant performance. However, plants are adapted to many aspects of their environments that are often excluded in the construction of seed transfer zones.
The study uses models that include combinations of geographic distance, climate distance, and soil metrics to predict plant mortality in an experimental garden for three species important to restoration in the southwestern United States: Bouteloua curtipendula, Heterotheca villosa, and Sporobolus cryptandrus. While climate distance performed better than geographic distance in predicting mortality, increasing climate distance was not consistently correlated with higher mortality, while geographic distance was.
Species responded uniquely to environmental gradients, indicating that site-specific details beyond climate may provide more accurate predictions. Seed sources from hotter, drier climates of H. villosa had improved survival during abnormally hot and dry weather, but there was no consistent signal in B. curtipendula or S. cryptandrus. These results indicate that more diverse seeding strategies may be important for successful restoration outcomes, especially when comprehensive, species-specific information is not available.
