LTREB: Long-Term Consequences of Asymmetric Warming at the Tundra-Taiga Interface

LTREB：苔原-针叶林交界处不对称变暖的长期后果

• 批准号: 2133494
• 负责人: Patrick Sullivan
• 金额: $ 59.99万
• 依托单位: University of Alaska Anchorage Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-01-01 至 2026-12-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2133494&HistoricalAwards=false
• 关键词: LTREB; Long; Term; Consequences; Asymmetric

The location of the Arctic treeline (the northernmost extent of trees) has important implications for carbon cycling, land surface energy exchange, wildlife habitat, and the availability of subsistence resources to Arctic human communities. The prevailing theory of treeline formation states that growth of treeline trees is strictly limited by cold growing-season air temperature. While this perspective is superficially supported by global-scale correlations between summer air temperature and treeline elevation, it is not supported by the observation that only about 50% of global treelines have advanced in response to anthropogenic climate warming. There is increasing evidence that other factors can determine treeline position, particularly in the Arctic. This project tests the hypothesis that warming winters with deepening snowpacks increase the growth and reproduction of treeline trees, thereby fueling treeline advance into Arctic tundra. Results are improving predictions of where and under what circumstances future treeline advance can be expected. The project provides education and training opportunities for graduate students and native residents of northwest Alaska. The Arctic is warming much faster than the rest of the globe and the warming is seasonally asymmetrical, with modest warming during the summer months and extreme warming during the winter months. In many regions of the Arctic, extreme winter warming is coupled with increasing snowfall. The combination of extreme winter warming and deeper, insulating winter snowpacks will lead to rapid winter soil warming, with wide-ranging consequences for ecosystem function. Warmer winter soils are generally associated with greater overwinter microbial activity, enhanced breakdown of soil organic matter, and a flush of nutrients that may be available for uptake by trees following snowmelt. This project leverages long-term observations of winter snowpack and corresponding tree growth in the Alaskan Arctic. It also extends a snowfence experiment, which builds deeper snowpacks around individual trees at three contrasting treelines. Long-term measurements are essential to identify the effects of seasonally asymmetric warming on treeline position in the Arctic, because of high interannual variability in winter weather and time lags associated with altered soil nutrient cycling, storage of resources in trees, and the episodic nature of tree investment in reproduction.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

北极树线（树木的最北端）的位置对碳循环、地表能量交换、野生动物栖息地以及北极人类社区生存资源的可用性具有重要影响。流行的树线形成理论指出，树线树木的生长受到寒冷的生长季节气温的严格限制。虽然这一观点表面上得到了夏季气温和树线海拔之间全球尺度相关性的支持，但只有大约50%的全球树线在应对人为气候变暖方面有所进展的观察结果并不支持。越来越多的证据表明，其他因素可以决定树线的位置，特别是在北极。该项目测试的假设是，冬季变暖，积雪加深，增加了树木的生长和繁殖，从而推动树木向北极苔原前进。结果是改善预测在哪里和在什么情况下，未来的树线前进可以预期。该项目为阿拉斯加西北部的研究生和土著居民提供教育和培训机会。 北极变暖的速度比地球仪其他地区快得多，而且变暖是季节性不对称的，夏季温和变暖，冬季极端变暖。在北极的许多地区，极端的冬季变暖伴随着降雪量的增加。极端的冬季变暖和更深的冬季隔热积雪相结合，将导致冬季土壤迅速变暖，对生态系统功能产生广泛的影响。温暖的冬季土壤通常与更大的越冬微生物活动，土壤有机质的分解增强，以及融雪后树木可吸收的营养素的冲刷有关。该项目利用了对阿拉斯加北极冬季积雪和相应树木生长的长期观测。它还扩展了一个雪栅栏实验，在三条对比鲜明的树线上的每棵树周围建立更深的积雪。长期测量对于确定季节性不对称变暖对北极树线位置的影响至关重要，因为冬季天气的年际变化很大，与土壤养分循环改变、树木中的资源储存、以及树木繁殖投资的偶发性。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准。