COS 187-6 - Can association genetics help guide seed selection for restoration plantings in a warming climate?

Background/Question/Methods

Climate change is motivating a reassessment of how seeds are selected for reforestation, as seed zones identified in the 20^th century may increasingly fail to represent populations best adapted to current local conditions. Comparisons of past seed source climate to projected climate of planting sites and the use of marker-assisted selection have potential to help, but combining these approaches has not been done on a large scale or been tested as part of an operational planting program. We are currently combining analyses of genetic markers (SNPs) associated with environmental gradients in sugar pine (P. lambertiana) and ponderosa pine (P. ponderosa) with an analysis of seedling survival and growth from a large-scale post-fire restoration experiment. Seedlings of both species from different elevation bands within the three nearest seed zones were planted in 2017, 2018, and 2019 at three sites within the King Fire burn scar. We aim to test A) whether seedlings from lower (warmer) elevations already perform better than local seed sources and B) whether seedlings with genotypes predicted to do well in the current planting site climate based on genetic associations identified in adult trees actually grow or survive better under field conditions.

Results/Conclusions

In both species, the majority of environment-associated SNPs were associated with average April 1^st snowpack – a factor that is changing rapidly as the climate warms. This may be because in the Mediterranean climate of California’s Sierra Nevada most precipitation comes as snow, and a thicker snowpack both insulates seedlings during winter and provides slow-release moisture for spring growth. Since 2017, the ponderosa pines from low-elevation sources (2,500 - 4000 ft) tend to exhibit better growth than the mid-elevation (4,001-5,000 ft) sources, which in turn grew more than the high-elevation (5001-6,000ft) seed sources, while survival was similar across seed sources. The low-elevation seed sources, on average, had similar snowpack and winter temperatures in 1921-1950 as the planting sites did in 1981-2010, further indicating the likely selective importance of snowpack. Survival of sugar pine seedlings was lower overall, but slightly higher for the lowest-elevation source (35% over 5 years for 3500-4000 ft compared to ~25%); Height growth, however, was highest for sources close to the local elevation (4500-5000 ft). Ponderosa pine seedling genotyping is currently ongoing. When this step is concluded, we plan to test whether including genotypes in Bayesian models of survival or growth improves the performance of these models.