DOI: 10.5061/dryad.vt4b8gv3q
title: Data from: Betting on rains that do not come: Monsoon failure and leaf area overshoot relate to increased tree mortality from drought

description: Structural overshoots, where biomass is overallocated to tree leaf area
 compared to sapwood area, could result in lethal stress during droughts.
 Climate change may alter climatic cues that drive leaf area production,
 such as temperature and precipitation, as well as seasonal dynamics that
 underlie summer rainfall due to the North American Monsoon (NAM).
 Combined, this could lead to temporal mismatches between leaf area-driven
 water demand and availability, and increased drought-induced mortality
 events. We used leaf area to sapwood area ratios to investigate the
 prevalence of overshoots and whether overshoots increase drought-induced
 mortality. We measured populations of aspen spanning the northern
 transition zone of the NAM during and following severe droughts. We
 observed increased overshoots and drought-induced mortality in southern
 latitude populations that rely more on summer monsoon rainfall. Changes in
 convective activity from low snowpack the preceding winter may be a
 climatic driver of heightened summer monsoon rainfall in the region and
 therefore may also trigger increased production of leaf area during wetter
 summers. Our results suggest that an overshoot of leaf area to sapwood
 area (AL:AS) ratios is associated with drought-induced tree mortality and
 highlight that climate-change driven alterations to the NAM could have
 major consequences for tree species’ acclimation to environment change.
   Supplemental data files provide for: Kerr KL, Anderegg LDL,
 Trugman AT, Anderegg WRL (2025) Betting on rains that do not come: Monsoon
 failure and leaf area overshoot relate to increased tree mortality from
 drought. Functional Ecology. Data were gathered from national forests (NF)
 throughout Utah and Colorado, USA in the summers of 2014, 2018, 2019,
 2020, and 2021. See Methods for details.
description: # Data from: Betting on rains that do not come: Monsoon failure and leaf
 area overshoot relate to increased tree mortality from drought Dataset
 DOI: [10.5061/dryad.vt4b8gv3q](10.5061/dryad.vt4b8gv3q) ## Description of
 the data and file structure Datafiles provided for: Kerr KL, Anderegg
 LDLA, Trugman ATT, Anderegg WRL (2025) Betting on rains that do not come:
 Monsoon failure and leaf area overshoot relate to increased tree mortality
 from drought Data were gathered from national forests (NF) throughout Utah
 and Colorado, USA in the summers of 2014, 2018, 2019, 2020, and 2021. See
 Methods for specific details on measurements. Three datasets are provided,
 and are described below: Kerr_fe_2024_01119_main_dataset.csv: This file
 contains the main dataset used in the analyses. Among its features are
 tree- and plot-level values for functional traits, leaf area to sapwood
 area ratios, and percent canopy dieback.
 Kerr_fe_2024_01119_dbh_sapwood.csv: This file contains the dataset used to
 generate the sapwood area (SA) allometric equations using Equation 2 as
 described in the methods. Kerr_fe_2024_01119_alltrees_dbh.csv: This file
 contains the dataset used to apply the SA equations to all trees in the
 plot and obtain plot-level estimates of sapwood area. Empty cells in these
 files reflect N/A (not applicable) data and are kept empty for easier
 uploading and correct interpretation in R. These data were not collected
 for that particular value. ### Files and variables #### File:
 Kerr\_fe\_2024\_01119\_metadata.csv **Description:** Metadata for
 supplemental data files provided for: Kerr KL, Anderegg LDL, Trugman AT,
 Anderegg WRL (2025) Betting on rains that do not come: Monsoon failure and
 leaf area overshoot relate to increased tree mortality from drought.
 Functional Ecology. #### File: Kerr\_fe\_2024\_01119\_main\_dataset.csv
 **Description:** This file contains the main dataset used in the analyses.
 Among its features are tree- and plot-level values for functional traits,
 leaf area to sapwood area ratios, and percent canopy dieback. #####
 Variables * year: Year of measurement * pop: Aspen population (For 2020:
 DIXIE=Dixie NF, SJNF=San Juan NF, UNCO=Uncompahgre NF, WR=White River NF,
 UINTA=Uinta NF) (For 2014-2019: names of plots within the San Juan NF of
 the form SpeciesCode-Elevation-plot_letter (e.g., POTR-H-A = high
 elevation aspen plot A) * elev: Elevation Band of species range (L: low
 elevation range margin, M: mid elevation range center, H: high elevation
 range margin). *Note: only applies to stands within the San Juan NF* *
 tree.tag: Tree # * plot: Sub plot for each population (or elevation band
 within the San Juan NF in 2014-2019) * dbh.cm: Tree diameter at breast
 height (~1.3m from ground) (cm) * age: Tree age based on increment cores
 (years) * lat: Latitude * long: Longitude * plot.elev.m: Plot elevation
 (m) * mean.elev.m: Mean elevation of all plots in the population (or
 elevation band within the San Juan NF in 2014-2019) (m) *
 plot.mort.percent: Plot-level mean canopy dieback scored during 2021 (all
 aspen populations) or 2019 (sub plots within the San Juan NF) (%) *
 july.precip: Precipitation total (mm) for month of July during the year of
 measurement (year column) * stem.length.mm: Length of the branch sample
 used for hydraulic conductance (mm) * stem.dia.mm: Stem diameter of branch
 sample used for hydraulic conductance (mm) * sapwood.dia.mm: Sapwood
 (xylem) diameter of branch sample used for hydraulic conductance (mm) *
 sapwood.area.m: Area of sapwwod basal area for branch sample used for
 hydraulic conductance (m^2) * knat: Branch-level native hydraulic
 conductivity (Knat, kg/s/m/kPa) * kmax: Branch-level maximum hydraulic
 conductivity (Kmax, kg/s/m/kPa) following embolism removal via vaccuum
 infiltration * PLC: Branch-level percentage loss of conductivity (kmax -
 knat)/kmax*100 (%) * leaf.area.m: Area of leaves on branch sample used for
 hydraulic conductance (m^2) * branch.al.as.mcm: Branch-level leaf area to
 sapwood area ratio (m2/cm2) * total.plot.sapwood.area.m: Plot-level total
 sapwood area determined using Equation 2 as described in the methods (m^2)
 * lai.LICOR: Plot-level LAI measured in 2018 for plots in the San Juan NF
 with the Licor LAI-2000 plant canopy analyzer (unitless) * lai.4ring:
 Plot-level LAI measured in 2020 for all aspen populations with
 hemispherical photos and Gap Light Analyzer software (unitless) * LAI.SA:
 Plot-level ratio of LAI to total sapwood area (m^-2) * bai.8total.m:
 Plot-level basal area increment (BAI) for the most recent 8 years of
 growth (2013-2020) for all aspen populations measured in 2020 (m^2) *
 bai.8.2018total.m: Plot-level basal area increment (BAI) for the most
 recent 8 years of growth (2011-2018) for the San Juan NF plots measured in
 2018 (m^2) * lai.bai8: Plot-level ratio of LAI to BAI for the most recent
 8 years of growth for all aspen populations measured in 2020 (m^-2) *
 lai.bai8.2018: Plot-level ratio of LAI to BAI for the most recent 8 years
 of growth for the San Juan NF plots measured in 2018 (m^-2) #### File:
 Kerr\_fe\_2024\_01119\_dbh\_sapwood.csv **Description:**  This file
 contains the dataset used to generate the sapwood area (SA) allometric
 equations using Equation 2 as described in the Methods. ##### Variables *
 pop: Aspen population (For 2020: DIXIE=Dixie NF, SJNF=San Juan NF,
 UNCO=Uncompahgre NF, WR=White River NF, UINTA=Uinta NF) * plot: Sub plot
 for each population * tag: Tree # * dbh: Tree diameter at breast height
 (~1.3m from ground) (cm) * sapwood.depth.cm: Sapwood depth measured on
 increment core (cm) #### File: Kerr\_fe\_2024\_01119\_alltrees\_dbh.csv
 **Description:** This file contains the dataset used to apply the SA
 equations to all trees in the plot and obtain plot-level estimates of
 sapwood area. ##### Variables * pop: Aspen population (For 2020:
 DIXIE=Dixie NF, SJNF=San Juan NF, UNCO=Uncompahgre NF, WR=White River NF,
 UINTA=Uinta NF) * plot: Sub plot for each population * dbh.cm: Tree
 diameter at breast height (~1.3m from ground) (cm) ## Code/software We
 used the freeware R (version 4.2.1) for all analyses. The following
 packages were used: lme4 (version 1.1.30) lmerTest (version 3.1.3) emmeans
 (version 1.8.3) car (version 3.1.0)