Climate and the Boreal Forest: Investigating Climatic Drivers and Effects of Climate Change at Multiple Scales

Evans, Andrew

ABSTRACT: Eastern North American boreal forests shifted poleward and upslope during the Holocene period, and anthropogenic disturbance and changing climate have accelerated that shift. To better understand the causes of northward shift, I performed a two-part analysis. First, I determined structure and composition across 45 plots in an ecotone between the temperate-deciduous forest community and a relict boreal-conifer community within undisturbed areas of Great Smoky Mountains National Park (GRSM). Analysis of those data suggested boreal forests are undergoing succession in structure and composition, from boreal-conifer dominated forests to a mixed composition that includes deciduous trees from the temperate-deciduous community. Under continued anthropogenic stress and a changing climate, temperate-deciduous species will continue to increase in dominance. Although boreal-conifer species will decrease, they will retain an understory presence. I then expanded analysis to the full continent. I created an ensemble Species Distribution Model (SDM) from paleo-pollen, forestry inventory, and gridded climate data. That analysis identified the climatic drivers of the ecotone between temperate-deciduous and boreal-conifer forests. Winter temperatures were important across all models, a result of frost damage caused by frost hardening and breaking of deciduous species. Growing season temperatures were significant in the paleo-pollen and relict boreal-conifer forest models, suggesting growth strategy and competition play a key role in maintaining community composition.