This article examines the adaptability of Douglas-fir across climatic gradients, evaluates the validity of existing seed transfer guidelines under changing climate conditions, and reports preliminary findings from regionally coordinated field trials
Drought, catastrophic wildfires, and increasing global demand for wood products are major stressors on both the wood supply chain and the ecosystem services provided by forested landscapes of the western United States. Seed supply from native forests and seed orchards is in high demand to support reforestation of drought- and wildfire-impacted lands, while maintaining industrial-scale forest management.
The need for seed transfer and knowledge gaps
Extensive research in the western United States has focused on the genetics of commercially and ecologically important conifer species, as well as their capacity to survive and thrive across landscapes with challenging moisture and temperature regimes. However, modern operational field research testing the limits of genotype × environment interactions on seed transferability remains limited. This gap is particularly significant for the Mediterranean and Continental climates of the interior Northwest.
Regionally, seed transfer guidelines across the interior Northwest and northern Rocky Mountains are typically based on decades-old provenance and progeny trials. These guidelines are often defined by latitude, longitude, elevation, and maximum distance from the seed source. A pressing question for forest managers is whether such guidelines remain valid in light of observed climate shifts over the past several decades and projected climate patterns. Several climate-based seed transfer models for western conifers have been developed to address these issues (O’Neill et al., 2014; Rehfeldt et al., 2014), but they have yet to be operationally tested.
Testing the limits of Douglas-fir seed transfer
Douglas-fir (Pseudotsuga menziesii) exhibits one of the widest ecological amplitudes of any conifer in the western United States, Europe, and New Zealand. Yet, it has relatively narrow seed transfer breeding zones due to its fine-tuned genetic adaptation to local climates. This adaptability raises several key questions:
- Are current seed transfer guidelines too restrictive, too broad, or outdated?
- How far is “too far” geographically and climatically?
- Does seed from a breeding zone remain viable in that same zone decades later?
- Should transfer guidelines be revised to reflect observed shifts in climate?
- Is assisted migration a viable strategy for a genetically diverse species such as Douglas-fir?
Douglas-fir seed transfer trials: the Intermountain Forestry Cooperative
To address these questions, the Intermountain Forestry Cooperative established a network of Douglas-fir seed transfer trials across the interior Northwest. Seed from wild (phenotypically superior native parents) and selected (genotypically improved orchard families) sources were identified, grown, and outplanted across a broad range of climatic and geographic conditions. Climate envelopes were constructed for all seed sources, and outplanted seedlings are being evaluated for survival and growth relative to local climatic regimes.
Preliminary results indicate that wild seed exhibits greater survival across a wider climatic range, while selected seed shows higher growth performance, though within a narrower climatic window. These findings suggest trade-offs between broad adaptability and growth potential. Ultimately, this research will inform the development of refined Douglas-fir seed transfer guidelines that optimize both survival and productivity under diverse climate conditions found across the interior Northwest, USA.
References
O’Neill, G. A., Stoehr, M., & Jaquish, B. (2014). Quantifying safe seed transfer distance and impacts of tree breeding on adaptation. Forest Ecology and Management, 328, 122–130. https://doi.org/10.1016/j.foreco.2014.05.039
Rehfeldt, G. E., Jaquish, B. C., Sáenz-Romero, C., Joyce, D. G., Leites, L. P., St. Clair, J. B., & López-Upton, J. (2014). Comparative genetic responses to climate in the varieties of Pinus ponderosa and Pseudotsuga menziesii: Reforestation. Forest Ecology and Management, 324, 147–157. https://doi.org/10.1016/j.foreco.2014.02.040
