Tue, Aug 03, 2021:On Demand
Background/Question/Methods
Because of the long generation times of trees, lags in ecological or evolutionary responses to rapid climate change could have negative impacts on forests. Potential management options include assisted migration or gene flow. However, the degree to which a species is locally adapted to climate, and how great a climatic transfer distance can they tolerate is often unclear. Moreover, factors such as competition from local vegetation may limit establishment success. We selected 13-14 source populations of ponderosa (Pinus ponderosa), Jeffrey (P. jeffreyi), and western white pines (P. monticola) to represent the full range of climatic conditions occupied by each species within California. Seedlings were planted in 2017 at four sites within Sequoia National park and have been monitored twice yearly for survival and growth. In 2020 this was replicated in Sierra and Tahoe National forests. Individuals will be removed before reproductive maturity.
Results/Conclusions Overall mortality differed greatly between plots, corresponding more with local natural seedling recruitment than elevation. Relative survival was greater, on average, for the locally dominant species at each plot; however, many populations survived better than average when transferred to sites that are slightly cooler or moister than their source, suggesting they are maladapted to current climate. This is consistent with a recent literature review we performed, in which 38% of tree species examined exhibited higher performance in sites 1-4 degrees cooler than home and an additional 23% showed no cost of moderately cooler conditions. Height growth, however, was highest at the lowest-elevation site and for lower-elevation species (ponderosa > Jeffrey > western white pine).
Results/Conclusions Overall mortality differed greatly between plots, corresponding more with local natural seedling recruitment than elevation. Relative survival was greater, on average, for the locally dominant species at each plot; however, many populations survived better than average when transferred to sites that are slightly cooler or moister than their source, suggesting they are maladapted to current climate. This is consistent with a recent literature review we performed, in which 38% of tree species examined exhibited higher performance in sites 1-4 degrees cooler than home and an additional 23% showed no cost of moderately cooler conditions. Height growth, however, was highest at the lowest-elevation site and for lower-elevation species (ponderosa > Jeffrey > western white pine).