Collaborative Research:Shifting Seasonality of Northern Forest Response to Arctic Environmental Change

AbstractThis award is funded under the American Recovery and Reinvestment Act of 2009（Public Law 111-5）.This is an investigation of the response of北方寒带森林对北极季节性变化的反应，使用现有的百年到千年树轮宽度和密度记录的环极网络，将与有针对性的实地观察，卫星数据和建模工作相结合。北方森林对北极变暖和相关季节性影响的敏感性可能是高度复杂的，涉及可能显著影响树木生长的多种因素的时间和动态变化。研究人员将评估基于网络的以及有限的新树木年轮数据，这些数据来自阿拉斯加东北部沿着纬度梯度的地点，阿拉斯加是当今地球仪上变暖最严重的地区之一。将沿沿着从南到北的梯度对研究中心进行采样，范围包括：1.内陆北方森林2.连续林线林和3.就在主林木线以北这些数据将被用来确定森林对整个温度范围内的季节性环境变化的反应的性质，该温度范围定义了白色云杉（一种主要的北极树线物种）生长的北方极限。它们还将确定最近的气候和森林生长变化相对于过去的自然变化是否具有独特性（可能是人为的）。相关性、卡尔曼滤波器、光谱分析和其他技术将有助于确定与最近变暖和气候季节性变化有关的任何阈值、随时间变化的变化或增长的非线性变化。超高分辨率、季节间和季节内树木生长数据（年轮宽度、最大晚材密度以及最小密度、早材和晚材宽度、可量化的木材解剖测量）将与每月温度、降水、干旱、土壤湿度和辐射观测数据进行比较，并在可能的情况下，与适合计算生长季节长度和其他季节参数的每周和每日记录进行比较。形成层生长模型将允许确定那些对北方森林生长影响最大的参数。季节内的生长信息将被应用到参数化的模型和事后控制的增长变化到过去使用的树木年轮数据。他们还将比较？在原地？树木年轮数据与高分辨率卫星派生的植被观测表明生长季节？绿化？然后呢？布朗宁？在北极圈森林生物群落的不同区域。因此，这一项目将提供一种手段，以测试协调遥感和地面监测的能力。在原地？北极北部森林生长活动的观测。

AbstractThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This is an investigation of the response of northern boreal forests to changes in arctic seasonality using an existing circumpolar network of centennial to millennial-length tree-ring width and density records that will be integrated with targeted field observations, satellite data and modeling efforts. The sensitivity of northern forests to arctic warming and related seasonality effects is likely to be highly complex, involving shifts in the timing and dynamics of multiple factors that can significantly impact tree growth. Researchers will assess network-based as well as limited new tree-ring data from sites along a latitudinal gradient in northeastern Alaska, one of the regions of greatest warming on the globe today. Sites will be sampled along a south to north gradient spanning from areas of: 1. interior boreal forest to 2. continuous treeline forest and 3. just north of main treeline. These data will be used to identify the nature of forest response to seasonal environmental changes across a temperature range that defines the northern limit of growth for white spruce, a dominant arctic treeline species. They will also determine if recent climate and forest growth changes appear unique (possibly anthropogenic) relative to past natural variability. Correlation, Kalman filter, spectral analyses and other techniques will allow identification of any thresholds, time-dependent changes or nonlinear shifts in growth linked to recent warming and changing climate seasonality. Ultra-high resolution, inter- and intraseasonal tree growth data (ring width, maximum latewood density as well as minimum density, early and latewood width, quantifiable wood anatomical measurements) will be compared to monthly temperature, precipitation, drought, soil moisture and radiation observations, and, where available, weekly and daily records suitable for computing the length of growing season and other seasonal parameters. A cambial growth model will permit identification of those parameters that are having the greatest impact on northern forest growth. Intraseasonal growth information will be applied to parameterize the model and hindcast controls on growth variations into the past using the tree-ring data. They will also compare the ?in situ? tree-ring data with high-resolution satellite-derived vegetation observations that have indicated growing season ?greening? and ?browning? in different regions of the circumpolar arctic forest biome. This project will thus provide a means to test the ability to coordinate remote sensing and ground-based ?in situ? observations of boreal forest growth activity in the Arctic.