Evidence for population differentiation among Jeffrey and Ponderosa pines in survival, growth and phenology

Ecological restoration projects that include reforestation require that land managers select appropriate source of seeds for long-term persistence. In California, the standard approach for making this choice is based on seed zone and elevational band, both geographically-based measures. However, given the pace of contemporary climate change, populations previously adapted to local conditions may become increasingly mismatched to the changes in climate. If there is a lag in adaptation, current seed zones which assume local is best, would be less useful for reforestation guidelines. Here we use a historic provenance test to evaluate genetic differences among provenances of two species of pine, Pinus ponderosa and P. jeffreyi, and assess performance following seedling transfer across an elevational gradient. Growth in Ponderosa pine shows evidence of a lag in adaptation: trees transferred from lower elevations had consistently increased growth when compared to those trees from higher elevations. In contrast, Jeffrey pine showed no evidence of a lag in adaptation for height. However, survival of Jeffrey pine provenances showed a significant quadratic relationship with transfer distance, consistent with local adaptation. In particular, Jeffrey pine trees from cooler, higher elevation sites had increased survival at high elevation. Jeffrey pine trees from higher elevation also exhibited earlier bud burst than trees from lower elevation grown in the same site, consistent with counter-gradient adaptation in phenology. Together, our results show that genetic variation within species is important for tree survival, growth and phenology in different climates. However, species-specific responses to elevational transfer indicates generalizing seed transfer guidelines across conifer species may be challenging and additional information is necessary to inform managed relocation in a changing climate.