Tree-ring Data from Treelines near the John River, central Brooks Range, Alaska, 1832-2021

The position of the Arctic treeline is an important regulator of land surface energy budgets, ecosystem-atmosphere carbon cycling, wildlife habitat and availability of subsistence resources to local communities. The prevailing hypothesis states that treeline position is determined by air temperature during the growing season. Because trees are taller than tundra vegetation and their canopy extends above the warmer boundary layer, their tissues are colder than tundra vegetation. These colder conditions are hypothesized to limit cell division and growth, such that seedlings are unable to grow into trees. However, our early work revealed that air temperature is warmer than previously thought near the Arctic treeline in Alaska and the indirect effects of temperature on soil nutrient availability may be important determinants of tree growth. We hypothesized that cold soils at treeline, particularly during winter, limit microbial activity and nutrient availability to the point where trees are barely able to survive and grow. This dataset contains tree-ring measurements made on increment cores collected in late August of 2021 at three treelines that varied in soil moisture and tundra vegetation near the John River in the central Brooks Range (Gunsight = dry heath tundra, Eagle Creek = mesic shrub tundra. Sheep Pond = wet sedge tundra). Our objective was to relate the tree-ring data to the weather record for Bettles, Alaska and test the hypothesis that winters with greater precipitation and/or deeper snow were associated with greater tree growth.北极林线（Arctic treeline）的位置是调控陆地表面能量收支、生态系统-大气碳循环、野生动物栖息地以及当地社区生计资源可获得性的关键因子。当前主流假说认为，林线位置由生长季的气温所决定。由于树木较苔原植被更为高大，且其冠层延伸至温度更高的大气边界层之上，因此树木组织的温度低于苔原植被。这类低温环境被假说认为会限制细胞分裂与植株生长，使得幼苗无法成长为成熟树木。然而，我们的早期研究发现，阿拉斯加北极林线附近的气温较此前认知水平更高，且气温对土壤养分可获得性的间接效应或许是调控树木生长的关键因素。我们据此提出新的研究假说：林线处的低温土壤（尤其是冬季）会抑制微生物活动与土壤养分供给，致使树木难以存活与生长。本数据集包含2021年8月下旬在阿拉斯加布鲁克斯山脉中部约翰河附近三处不同土壤湿度与苔原植被类型的林线采集的树木生长钻芯（increment core）的年轮测量数据。三处林线分别为：Gunsight（干石楠苔原）、Eagle Creek（中生灌丛苔原）、Sheep Pond（湿生薹草苔原）。本研究的目标是将树木年轮数据与阿拉斯加贝茨（Bettles）的气象记录进行关联分析，并验证"冬季降水量更高或积雪更深与树木生长更旺盛相关"这一研究假说。