Sampling spruce growth and climate sensitivity on glacial rivers of Alaska

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Glenn Juday
Claire Alix
Steve Winslow

 We are examining the growth, growth history and climate sensitivity of white and black spruce trees on the floodplains of the major rivers fed by glacial meltwater in Interior Alaska. To date we have sampled 624 trees on 41 sites distributed across 1,783 km of the Yukon River, 375 km of the Tanana River, and 370 km of the Kuskokwim River, for a total of 2,528 km of river length. We have analyzed the climatic control of radial growth in 146 large, dominant white spruce trees from 7 sites on the floodplain of the Yukon River, two stands on the Tanana River in BNZ LTER, and 188 white spruce and 77 black spruce trees along the Kuskokwim River. Measurement files were cross-dated with very high confidence of year-to-year correspondence. These trees enter rivers when erosion, which is very active, undercuts the banks and the trees topple into the water. Trees are transported into the Bering Sea and Arctic Ocean. This type of coarse woody debris is one of the main tangible exports of biological material from BNZ LTER. The growth of Interior spruce trees is negatively sensitive to temperature and weakly positive to precipitation, a pattern that is consistent for at least 150 years. Recent years have been the least climatically favorable for the past two centuries at least because of sustained warmth. Spruce populations in cooler maritime climate regions of western Alaska predominately include trees whose growth responds positively to warmth, with a transition zone between the Interior and maritime regions. Our results indicate that recent warming has strong stressed spruce in many Interior locations and has already created an optimum climate region in western Alaska with smaller trees or only young trees.