Mixed-provenance plantings and climatic transfer-distance affect the early growth of knobcone-monterey hybrid pine, a fire-resilient alternative for reforestation

Given increasing forest disturbances, novel solutions are needed to rapidly recover ecosystem services such as carbon storage, while bolstering climate change adaptation. Reforestation with single-species mixed-provenance plantings is an emerging strategy that may enhance stand productivity and disturbance resistance, while assisted gene flow is a potentially powerful tool for matching seed-source with future planting-site climate. We investigated the potential of mixed-provenance plantings and assisted gene flow for maximizing early growth using a historical dataset for knobcone-Monterey pine (Pinus x attenuradiata), a fire-resilient hybrid developed for low-elevation sites in California, USA. We examined (1) 9-year individual-tree relative growth rate (RGR) in response to neighborhood seed-parent provenance diversity at two test sites and (2) 3-year RGR and survival as functions of parent seed-source climate at 4 test sites. We found 9-year RGR varied with seed provenance diversity, with 3 of 5 provenances showing a positive RGR-diversity relationship. Parent seed-source climate affected 3-year RGR but not survival. Closer climate matches in terms of precipitation as snow (PAS) showed fastest growth. Our results suggest careful selection and arrangement of genetically diverse stock may improve carbon sequestration and initial planting success in a hybrid conifer, with implications for reforestation under climate change and reburn risk.