DOI: 10.5061/dryad.6hdr7sr08
title: Data from:Radial growth decline of White Spruce (Picea glauca) during hot summers without drought: Preliminary results from a study site south of a boreal forest border

description: Climate warming and more frequent droughts threaten the effectiveness of
 circumpolar boreal forests as carbon sinks.  To the immediate
 south of boreal forests in eastern North American lie regions that still
 support natural island-like growths of boreal conifers, where warming
 (expressed by higher temperature maxima) has increased at similar rates
 but with seasonal precipitation increases rather than the decreases that
 are commonly seen in other warming regions.  Studying tree growth
 under these circumstances offers the opportunity to examine effects of
 heat stress in the absence of drought.  We studied growth of
 mature White spruce (Picea glauca), planted as pure stands in east-central
 New York State, at the top of the Helderberg Plateau (600 m above sea
 level) during the 1920s. During 2013-2017 period we observed 1) radial
 growth of spruce trees, 2) sap flow, 3) soil moisture in the top 10 cm
 layer as well as timing of spruce budbrake and detailed survey of tree
 species at two 30x30 meters plots.  Results demonstrate that the
 spruce responded to the early arrival of a warmer-than-average spring with
 a 3-4 day advance in the start of radial growth (SRG).  During
 the same years, the end of radial growth in late summer occurred earlier
 by 14-18 days indicating a cessation in growth despite moist
 soils and favorable solar conditions. Therefore, the observed advance in
 the SRG did lead to a shorter radial growth period due to early cessation
 dates.  Abundant precipitation and relatively high soil moisture
 supported relatively stable sap flow and allowed us to dismiss soil
 drought as a factor.   If heat stress is leading to
 declines in photosynthesis, a likely explanation based on previous
 experimental work on this species, reduced allocation of non-structural
 carbon to tree stems leads to early cessation of radial growth and
 therefore reduced carbon storage, independent of seasonal
 precipitation. 
description: This work took place in the
 Edmund Niles Huyck Preserve (42.5155° N, 74.1402° W https://phenocam.sr.unh.edu), an 800 ha nature preserve and biological research station established in 1931 about 300 km south of the southern border of the boreal forest biome.  The preserve is located on the Helderberg Plateau within the Glaciated Low Allegheny Plateau Ecoregion. We surveyed and mapped two 30x30 m plots within White spruce (<i>Picea glauca</i>) plantations begun as seedlings in 1924-1927. The plots are separated by 1500 m and lie uphill from two different water bodies Lincoln Pond (LP) and Lake Myosotis (LM). Locations of all trees &gt;10 cm dbh were mapped.  Radial growth of trees during 2013-2017 was monitored with six ICT high resolution ( <i>±</i> 0.001 mm) two-point dendrometers at 30 min intervals. These records were averaged over 24 h intervals to match the resolution of weather data. In addition to radial growth, every spring we recorded the date of budbreak. This final stage of bud break was estimated directly by visual inspection of the spruce canopy as the day when bud scales burst and fresh needles became visible. Volumetric soil moisture content was measured in the top 10 cm of soil profile in 2016 at LP and LM sites and in 2017 at only LP site. These measurements were derived from 5 “wave” soil moisture sensors (MP3063, ICT International), with 3 sensors installed at the LP site and 2 sensors at LM site.  The rate of radial growth was modeled with partial least square regression (PLSR) with a nonlinear iterative partial least squares (NIPALS) algorithm that uses the Variance Inflation Factor (VIF) to measure the impact of collinearity among the variables in a regression model. 
description: File
 Contains raw and modeled
 data. 
 Survey_LP_LM_plots 
 Coordinates of 106 trees with species name, diameter at breast
 height (dia), and field notes. 
 LPSpruce,
 LMSpruce Maps of two surveyed plots of white
 spruce with marked locations of used instrumentation. 
 
 Radialgrowth  
 Radial growth increments of six white spruce trees during
 2013-2017 seasons and GAM smoothed models.  
 
 lpsoilmoist_2016, lpsoilmoist_2017, lmsoilmoist_2016
 Soil moisture records from two soil
 moisture meters located at LP and ML plots. 
 
 PLSR_modeling1 Estimates of VIP for each year of
 observations (variables with VIP&gt;1 are considered statistically
 significant.   
 PLSR_modeling2 Loading Coefficients of Variables in
 the first Principal Component of PLSR models. 
 
 PLSR_modeling3 Estimates of adjusted coefficient of
 determination and the Variable Inflation Factor for PLSR models with one
 principal component and two variables with largest VIP.