Environment and Natural Resources Institute, University of Alaska Anchorage, Anchorage, AK, 99508, USA.
Pacific Northwest Research Station, USDA Forest Service, Anchorage, AK, 99503, USA.
Sci Rep. 2017 Nov 10;7(1):15344. doi: 10.1038/s41598-017-15644-7.
Boreal forests play critical roles in global carbon, water and energy cycles. Recent studies suggest drought is causing a decline in boreal spruce growth, leading to predictions of widespread mortality and a shift in dominant vegetation type in interior Alaska. We took advantage of a large set of tree cores collected from random locations across a vast area of interior Alaska to examine long-term trends in carbon isotope discrimination and growth of black and white spruce. Our results confirm that growth of both species is sensitive to moisture availability, yet show limited evidence of declining growth in recent decades. These findings contrast with many earlier tree-ring studies, but agree with dynamic global vegetation model projections. We hypothesize that rising atmospheric [CO] and/or changes in biomass allocation may have compensated for increasing evaporative demand, leaving recent radial growth near the long-term mean. Our results highlight the need for more detailed studies of tree physiological and growth responses to changing climate and atmospheric [CO] in the boreal forest.
北方森林在全球碳、水和能量循环中发挥着关键作用。最近的研究表明，干旱导致北方云杉生长衰退，预计在阿拉斯加内陆地区会出现广泛的死亡和植被类型的转变。我们利用从阿拉斯加内陆广大地区随机地点采集的大量树木芯样，研究了黑云杉和白云杉的长期碳同位素分馏和生长趋势。我们的研究结果证实，这两个物种的生长都对水分供应敏感，但在最近几十年中，生长速度下降的证据有限。这些发现与许多早期的树木年轮研究结果相反，但与动态全球植被模型的预测结果一致。我们假设，大气[CO]的上升和/或生物量分配的变化可能补偿了蒸发需求的增加，使得最近的径向生长接近长期平均值。我们的研究结果强调，需要对北方森林中树木生理和生长对气候变化和大气[CO]变化的响应进行更详细的研究。
