Modeling spatial variability of white spruce (Picea glauca) growth responses to Climate Change at and below treeline in Alaska - A case study from two National Parks

Abstract

Aim of this study was to develop a spatially explicit, medium-scale model of the climate sensitivity of recent white spruce growth at and below treeline in Denali National Park (DNP) and Gates of the Arctic National Park (GAAR) in Alaska and then use the model to project changes in extent of boreal forest under future warming scenarios. We developed a decision-tree model to examine tree growth-environment relationships and used a GIS to extrapolate model results into space. In DNP our results indicate possible dieback of white spruce at low elevations and treeline advance and infilling at high elevations. If recent warming continues, the road corridor in DNP would experience forest increase of about 50%, mainly along the road decreasing the possibility for visitors to observe wildlife across open tundra. In GAAR our results indicate increased rate of white spruce growth at low elevation areas while other areas would experience changes in forest structure (dieback of tree-islands, infilling of existing stands). Changes in distribution of white spruce forests in Alaska are within the range of possibility on a regional scale (treeline advance, dieback). Structural changes within existing forest are possible on a medium (landscape) scale through changes in tree density, infilling and dieback. Changes in growth performance of individual trees due to climate warming are already underway, and further warming would intensify these changes with landscape-wide consequences.