DOI: 10.5061/dryad.9w0vt4bsm
title: Tree-ring width, and tree-ring stable carbon isotope data from SW Alaska

description: These data include tree-ring chronologies and stable carbon isotope data
 for locations in southwestern Alaska that were used in the study
 Decoupling of temperature and growth of white spruce at western treeline,
 Alaska is unrelated to intrinsic water stress. The ring-width index (RWI)
 chronologies were produced by first removing age-related declines in
 growth by fitting a modified negative exponential curve, or a zero-slope
 curve if there were no age-related declines, to each ring-width series and
 then by averaging the individual indices together using a Tukey bi-weight
 robust mean (Cook and Kairiukstis 1990) using the dplR package (Bunn 2008)
 in R (R Core Team 2018). RWI is a dimentionless index used for tree ring
 chronologies. Carbon stable isotope chronologies were produced for a 30-50
 year period from each side. Wood was sub-sampled to alpha cellulose using
 the modified Brendel et al. (2005) method (Gaudinski et al. 2011) and
 analyzed at the University of Arizona, Environmental Isotope Laboratory.
 Uncorrected Carbon isotopes (δ13C) are provided with the units in per mil.
 Analytical error is 0.03 per mil. δ13C was converted
 to 13C discrimination (Δ13C) to correct for changing atmospheric
 δ13CO2 since the Industrial Revolution and is also provided in the data
 set. 
description: # Tree-ring width, and tree-ring stable carbon isotope data from SW Alaska
 Dataset DOI: [10.5061/dryad.9w0vt4bsm](10.5061/dryad.9w0vt4bsm) ##
 Description of the data and file structure The study sites comprise a
 subset of a larger network of monitoring plots on the northern Alaska
 Peninsula, on and adjacent to National Park Service lands (Csank et al.
 2016; Sherriff et al. 2017). At each site, we preferentially cored a
 minimum of 20 mature, large diameter canopy trees at a distance of at
 least 10 m from one another. At forest sites we sampled trees &gt;20 cm
 DBH and &gt;10 m in height. At woodland sites, where trees were smaller,
 we sampled trees &gt;8 cm DBH. Additional details regarding field methods
 can be found in previously published studies from these sites (Csank et
 al. 2016; and Sherriff et al. 2017).  Cores were collected at 30-50 cm
 above the root crown and crossdated using standard dendrochronological
 techniques (Stokes and Smiley 1996). Tree-ring widths for each core were
 counted using a binocular scope, measured to 0.001 mm using WinDendro
 (Regent Instruments, Inc.) at a scan resolution of 600-1200 dpi, and were
 visually and statistically crossdated using the COFECHA program (Holmes et
 al. 1983). We generally found very consistent inter-series growth patterns
 within sites, with inter-series correlations averaging 0.47 across sites. 
 Prior to detrending long-term growth trends and averaging the individual
 indices, we grouped the cores from each site according to their recent
 growth patterns to develop separate chronologies for the following: (1)
 trees that exhibited at least a 2-fold increase in growth during the most
 recent 10 years, relative to growth in the prior decade; and (2) trees
 that showed reduced or stationary growth over the same period (n = 6-10
 cores per group). Two sites affected by beetle kill included separate
 chronologies from live and dead trees, both of which were identified as
 having reduced or stationary growth. A third beetle kill site included
 cores from dead trees only. The groupings allowed us to differentiate
 between trees with recent growth increases well above long-term growth
 trends (i.e., &gt;2-fold increase in the most recent decade) from other
 trees at the same site that showed declining or stationary growth. It is
 possible that some trees identified as having stationary growth could have
 been grouped with trees showing increasing growth if we had used a lower
 threshold (e.g. 1.5x), but we believe that the 2x threshold effectively
 captures the variation in growth patterns that we observed at our sites.
 Five sites had chronologies that showed only increasing growth, two sites
 had only stationary growth, and four sites included separate chronologies
 that showed both increasing and stationary growth.  For more details
 please see Miller et al. (2025) Ecology ### Files and variables #### File:
 Miller\_et\_al\_2025\_Ecology\_AK\_Spruce\_Data.xlsx
 **Description:** Excel worksheet contains 4 sheets. The first is metadata
 including site locations, species, coordinates and time period covered.
 The second worksheet is RWI for each site, the third is the raw carbon
 isotope data and the fourth is the corrected carbon isotope discrimination
 data. Data were corrected using the Point Barrow d13CO2 and PCO2 data.
 Missing data is indicated as 'NaN' ##### Variables * RWI
 (dimentionless) * d13C (raw) (per mil) * D13C (discrimination) (per mil)
 ## Code/software The R statistical program was used with the packages
 dplR.  ## Access information Other publicly accessible locations of the
 data: * These data will also be uploaded to the ITRDB