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Measurements of treeline white spruce needle carbon, nitrogen and phosphorus concentrations, along with stable isotopes of carbon and nitrogen. Samples were collected of the most recent needle cohort at breast height in August and September. The purpose of this dataset was to examine spatial variation in white spruce needle nutrition and gas exchange physiology across the Brooks Range and in relation to local microclimates. The 2021 and 2022 datasets contain data for treeline trees that were treated with NPK fertilizer at a sub-set of the research sites. 

Measurements of treeline white spruce needle length and needle mass per unit projected needle area on needles produced and sampled 2019, 2021 and 2022. Measurements of needle length and projected area were made using WinSeedle software on scans of the needle samples. The purpose of of this dataset was to examine spatial variation in treeline white spruce needle attributes across the Brooks Range and in relation to local microclimates. 

This dataset includes measurements and estimated variable values from treelines in Alaka's Brooks Range mountains. It includes locations of colonists above treelines found in 2018, 2019, 2020, 2021, and 2022; forest advance rates from the 1970s to 2010s from repeat imagery; growth rates of leaders of juveniles during 2015-2020 and lateral branch growth of adults in 2019; counts of saplings; temperatures of air at 2 meters (m) and soil at 10 centimeters (cm) from 2019-2022; soil moisture in 2019; estimated snow depth in January 2020, 2021, and 2022; foliar nitrogen and phosphorous; and foliar stable isotope ratios for nitrogen (15N:14N) and carbon (13C:12C). The purpose of the dataset is to show the effect of sea ice retreat on treeline advance. 

We destructively sampled up to 15 white spruce (Picea glauca) seedlings (<140 centimeters tall) from 2 study treelines (1 upper elevation, Alpine, and 1 lower elevation, Arctic) at 16 sites across Alaska's Brooks Range in August-September 2021. We harvested 3 seedlings each in 5 height classes (0-10, 10-30, 30-60, 60-100, 100-140cm). Height (cm) was measured in the field before harvest as vertical distance from ground to tallest living tissue. The target of harvest was the root-shoot boundary, where above ground stem interfaces with roots. The earliest years of a seedling should be located in the wood of this section. For very small seedlings we harvested whole seedlings. In the laboratory we cut ~1cm thick "cookies" of the harvest root-shoot section, progressively sanded until cells were visible under the microscope and then counted rings back to the pith. For small seedlings, we counted bud scars along the stem. We used the earliest date obtained from these counts as the germination date (the innermost year, or In.year in the data csv). The general purpose of the sampling was to examine west-east variation in white spruce growth and reproduction responses to changes in climatic gradients and ongoing climate change. 

Measurements of treeline white (Picea glauca) and black (P. mariana) spruce abundance during 2019, 2020, 2021 and 2022 as sampled within n = 695 5-meter (m) radius plots (area = 78.5 square meters), each centered on a selected white spruce adult called "Focal Tree". Measurements included height of stems between 0.5 and 1.4 m tall and diameter at 1.4 m for individuals taller than 1.4 m. Those individuals taller than 1.4 m tall were also stem mapped in polar coordinates with r = distance and theta as magnetic direction from a focal center white spruce tree. The purpose of this dataset was to examine spatial variation in treeline white spruce densities and basal area across the Brooks Range and in relation to local microclimates. It also provides a baseline for future stem mapping to determine changes in abundance. 

Stem counts of tall shrubs (height from 0.3 to greater than 2 meters) during 2019, 2020, 2021 and 2022 as sampled within n = 594 5-meter radius plots (area = 78.5 square meters), each centered on a selected white spruce adult called "Focal Tree". The purpose of this dataset was to examine spatial variation in tall shrub densities of the most important genera across the Brooks Range and in relation to local microclimates. It also provides a baseline for future shrub stem counts to determine changes in abundance. 

This data set represents 23 study sites across 22 degrees of longitude along treeline in Alaska's Brooks Range. Each study site was approximately 50 square kilometers in area and sampled with approximately n = 3,000, randomly-placed 6 meter (m) diameter disks. Each of the 63,224 disks were classified by humans into coarse vegetation classes twice, once using 1970s aerial orthophotos (e.g., Alaska High-Altitude Photography) and again using 2010s very-high resolution satellite imagery (e.g., MAXAR World-View). In addition, annual maximum Landsat normalized difference vegetation index (NDVI) values were extracted from a subset of these disks (n = 27,835 from 12 study sites) for Theil-Sen regression on greening trends using the R package LandsatTS. 

Cover rankings of ground cover during 2019, 2020, 2021 and 2022 as sampled within n = 553 5-meter (m) radius plots (area = 78.5 square meters), each centered on a selected white spruce adult called "Focal Tree." The purpose of this dataset was to examine spatial variation in ground cover (less than 0.2-0.3 m tall) of the most important genera across the Brooks Range and in relation to local microclimates. It also provides a baseline for future ground cover rankings to determine changes in abundance. Taxa were ranked in order of cover from Rank1 with the most cover down to Rank5 with the lowest cover in most cases. 

Photograph-derived counts of seed cones on white spruce (Picea glauca) trees at elevational (alpine) & lower (arctic) treelines at 19 research sites along a west-east gradient in Alaska's Brooks Range. Photographs are from a single angle and thus represent a "cone production index" rather than a complete count of all the cones on a tree. The general purpose of the sampling was to examine west-east variation in white spruce growth and reproduction responses to changes in climatic gradients and ongoing climate change. 

Measurements of air temperature at 2 meter height made along elevation gradients from the valley bottom to the alpine at 16 sites along a west to east gradient in the Brooks Range. The purpose of this dataset was to examine spatial variation in white spruce needle nutrition and gas exchange physiology across the Brooks Range and in relation to local microclimates.