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Alaska's Changing Boreal Forest$
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F. Stuart Chapin, Mark W. Oswood, Keith Van Cleve, Leslie A. Viereck, and David L. Verbyla

Print publication date: 2006

Print ISBN-13: 9780195154313

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195154313.001.0001

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Summary and Synthesis: Past and Future Changes in the Alaskan Boreal Forest

Summary and Synthesis: Past and Future Changes in the Alaskan Boreal Forest

(p.332) 21 Summary and Synthesis: Past and Future Changes in the Alaskan Boreal Forest
Alaska's Changing Boreal Forest

Marilyn W. Walker

Mary E. Edwards

Oxford University Press

Historically the boreal forest has experienced major changes, and it remains a highly dynamic biome today. During cold phases of Quaternary climate cycles, forests were virtually absent from Alaska, and since the postglacial re-establishment of forests ca 13,000 years ago, there have been periods of both relative stability and rapid change (Chapter 5). Today, the Alaskan boreal forest appears to be on the brink of further significant change in composition and function triggered by recent changes that include climatic warming (Chapter 4). In this chapter, we summarize the major conclusions from earlier chapters as a basis for anticipating future trends. Alaska warmed rapidly at the end of the last glacial period, ca 15,000–13,000 years ago. Broadly speaking, climate was warmest and driest in the late glacial and early Holocene; subsequently, moisture increased, and the climate gradually cooled. These changes were associated with shifts in vegetation dominance from deciduous woodland and shrubland to white spruce and then to black spruce. The establishment of stands of fire-prone black spruce over large areas of the boreal forest 5000–6000 years ago is linked to an apparent increase in fire frequency, despite the climatic trend to cooler and moister conditions. This suggests that long-term features of the Holocene fire regime are more strongly driven by vegetation characteristics than directly by climate (Chapter 5). White spruce forests show decreased growth in response to recent warming, because warming-induced drought stress is more limiting to growth than is temperature per se (Chapters 5, 11). If these environmental controls persist, projections suggest that continued climate warming will lead to zero net annual growth and perhaps the movement of white spruce to cooler upland forest sites before the end of the twenty-first century. At the southern limit of the Alaskan boreal forest, spruce bark beetle outbreaks have decimated extensive areas of spruce forest, because warmer temperatures have reduced tree resistance to bark beetles and shortened the life cycle of the beetle from two years to one, shifting the tree-beetle interaction in favor of the insect (Chapter 9).

Keywords:   anchor ice, biogeochemistry, forest dynamics, ignition, nitrogen limitation, organic nitrogen, species richness, turning point

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