An ecological and climatic transition zone: warming, disturbance and forest response in Southwest Alaska

Keywords: Forests, boreal, climate change, dendroecology, Alaska
Session Type: Virtual Paper
Day: Wednesday
Session Start / End Time: 4/7/2021 01:30 PM (Pacific Time (US & Canada)) - 4/7/2021 02:45 PM (Pacific Time (US & Canada))
Room: Virtual 9

Abstract

Recent warming has impacted growth, recruitment, and mortality in high-latitude forests, and models suggest that increasing temperatures will lead to increases in net primary production and potential range shifts. Warming has also been linked to growth declines and tree mortality. Southwest Alaska marks an ecological and climatic transition zone between interior Alaska, where summers are warmer and drier, and western Alaska, where summers are cooler and wetter. Recent growth declines in black and white spruce (Picea mariana; P. glauca) across interior Alaska and western Canada have been attributed to warm summers and temperature-induced drought stress. This presentation reviews our current understanding from dendroecological (i.e., growth, isotopes, stand structure, disturbance) studies in Southwest Alaska showing mixed responses of white spruce to warming in recent decades, with divergent responses across a range of environmental conditions including: 1) Forest expansion; 2) restriction of spruce beetle disturbance to the central and western regions; 3) low spruce beetle mortality, and favorable responses to recent warm-season temperatures by the dominant woodland forest type; 4) high spruce beetle mortality, and declines in growth in dense forests; and 5) inference that temperatures have yet to exceed a physiological threshold resulting in severe drought stress, or that trees are compensating for water limitation through conservative strategies, which contrasts tree-ring records from interior Alaska showing declines in carbon isotopes, and/or increases in water-use efficiency concurrently with growth declines.