DOI: 10.5061/dryad.s4mw6m9fw
title: Data from: Linking physiological drought resistance traits to growth and mortality of three northeastern tree species

description: Climate change is raising concerns about how forests will respond to
 extreme droughts, heat waves, and their co-occurrence. In this greenhouse
 study, we tested how carbon and water relations relate to seedling growth
 and mortality of northeastern US trees during and after extreme drought,
 warming, and combined drought and warming. We compared the response of our
 focal species red spruce (Picea rubens Sarg.) to a common associate (paper
 birch, Betula papyrifera Marsh.) and a species expected to increase
 abundance in this region with climate change (northern red oak, Quercus
 rubra L.). We tracked growth and mortality, photosynthesis, and water use
 of 216 seedlings of these species through a treatment and a recovery year.
 Each red spruce seedling was planted in containers either alone or with
 another seedling to simulate potential competition and seedlings were
 exposed to combinations of drought (irrigated, 15-day ‘short’, or 30-day
 ‘long’) and temperature (ambient or 16 days at +3.5 ℃ daily maximum)
 treatments. We found dominant effects of the drought reducing
 photosynthesis, midday water potential, and growth of spruce and birch,
 but that oak showed considerable resistance to drought stress. The effects
 of planting seedlings together were moderate and likely due to competition
 for limited water. Despite high temperatures reducing photosynthesis for
 all species, the warming imposed in this study minorly impacted growth
 only for oak in the recovery year. Overall, we found that the diverse
 water-use strategies employed by the species in our study related to their
 growth and recovery following drought stress. This study provides
 physiological evidence to support the prediction that native species to
 this region like red spruce and paper birch are susceptible to future
 climate extremes that may favor other species like northern red oak,
 leading to potential impacts on tree community dynamics under climate
 change.
description: # Data from: Linking physiological drought resistance traits to growth and
 mortality of three northeastern tree species
 [https://doi.org/10.5061/dryad.s4mw6m9fw](https://doi.org/10.5061/dryad.s4mw6m9fw) Produced by Alexandra Barry. 2024-07-25. a.m.barry15[at]gmail.com. This research was supported by ME0-42121, USDA McIntire-Stennis Program, administered through the Maine Agricultural and Forest Experiment Station. This research was also supported by the University of Maine School of Forest Resources (SFR). This dataset contains data collected during a two-year greenhouse experiment using containerized seedlings of *Picea rubens* (Sarg.), *Quercus rubra* (L.), and *Betula papyrifera* (Marsh.). The goal of this study was to examine the photosynthesis and water use responses of seedlings growing as individuals and in competition with current and future associates, and how these responses affect mortality and growth among these species. The 'treatment year' (2022) included planting of bare-root seedlings in containers, growth and vigor measurements, gas exchange measurements including photosynthesis and stomatal conductance, midday leaf water potential measurements, and measurements/analysis to calculate species-level drought resistance traits including osmotic potential at turgor loss (turgor loss point, TLP), minimum epidermal conductance during drought (gmin), leaf water potential at 90% stomatal closure (gs90). The 'recovery year' began at the end of the growing season in 2022 and included a full growing season during which seedlings were not subject to experimental stressors. Height, stem diameter, and brown foliage of seedlings were measured at the end of the growing season in 2022, and again at the end of the growing season in 2023 once seedlings had been in 'recovery' (not receiving warming or drought treatment) for one year. The difference between minimum midday leaf water potential and species TLP was modeled as a predictor variable for end-of-season relative growth in order to determine whether degree of water stress could predict seedling growth shortly after stress or after stress recovery. Data were entered by hand on paper, then entered in Microsoft Excel and saved as .csv to be analyzed in R. All calculations and statistical analyses were performed in R (R version 4.2.3; R Core Team 2023), using RStudio (RStudio Team, 2023). ## Description of the data and file structure **Soil Moisture Log_2022.csv** - log of container planting media (informally, 'soil') moisture values from beginning to end of experiment in 2022. Measured using a 12-cm probe measuring volumetric water content (VWC) of container media, inserted halfway between the stem and the container edge on two sides of the media. Columns are as follows: Date: in mm/dd/yyyy format, the date on which diameter measurement was recorded in 2022. Tree.ID: unique ID number associated with a single seedling. Seedlings planted together in one container each had a unique ID number. ID numbers were assigned upon planting. Any missing ID numbers were seedlings removed prior to the beginning of the experiment. species: seedling species. piru =* Picea rubens* (red spruce), quru =* Quercus rubra* (northern red oak), bepa =* Betula papyrifera* (paper birch) drought treatment: one of three drought treatment levels, assigned to each container. long = long drought (30 days water reduction); short = short drought (15 days water reduction); irrigated = no water reduction, container irrigated to field capacity. N/A values indicate this seedling was measured as an 'extra' control but was not assigned an experimental treatment. warm treatment: one of two warming treatment levels assigned to each container, by half-block. heat = 15-day passive warming, ambient = no warming, ambient greenhouse temperatures throughout. N/A values indicate this seedling was measured as an 'extra' control but was not assigned an experimental treatment.  percent sm 1: first value of VWC in a single container percent sm 2: second value of VWC in the same container, measured across the container from the first measurement average soil moisture: average of percent sm 1 and 2, used in analysis **Greenhouse Diameter 2022.csv** - contains measurements of seedling stem diameter recorded during the 2022 'treatment year.' During each measurement campaign, each seedling was measured at two perpendicular points on the stem 3 cm from the soil surface and these measurements were averaged into a single value. This document also contains columns used to calculate values of relative stem diameter growth (diameter growth of stem relative to diameter at beginning of season). Columns are as follows: Tree.ID: unique ID number associated with a single seedling. Seedlings planted together in one container each had a unique ID number. ID numbers were assigned upon planting. Any missing ID numbers were seedlings removed prior to the beginning of the experiment. Measurement.round: unique number of measurement iteration, 1-6. Because a round of measurements was sometimes done over a period of two days, we assigned a single measurement round number to each iteration of measurements. species: seedling species. piru =* Picea rubens* (red spruce), quru =* Quercus rubra* (northern red oak), bepa =* Betula papyrifera* (paper birch) drought treatment: one of three drought treatment levels, assigned to each container. long = long drought (30 days water reduction); short = short drought (15 days water reduction); irrigated = no water reduction, container irrigated to field capacity. N/A values indicate this seedling was measured as an 'extra' control but was not assigned an experimental treatment. warm treatment: one of two warming treatment levels assigned to each container, by half-block. heat = 15-day passive warming, ambient = no warming, ambient greenhouse temperatures throughout. N/A values indicate this seedling was measured as an 'extra' control but was not assigned an experimental treatment.  avg.diam.mm: average of two stem diameter measurements taken 3 cm from soil surface, in millimeters. doy: day of year that the measurement was taken in 2022. diam.start: stem diameter of each seedling at first measurement (beginning of 2022 season). This value should equal avg.diam.mm at Measurement.round 1. rel.diameter: a percentage value indicating a percent change in stem diameter relative to starting stem diameter.  competition: one of six competition treatment levels, assigned to individual seedlings. single = planted alone; comp-piru = planted with a spruce seedling; comp-quru = planted with an oak seedling; comp-bepa = planted with a birch seedling block: ID number of experimental block, 1-4. half.block: ID of experimental half-block, each half of an experimental block assigned to either a warming treatment or no warming. Format is treatment_block ID. **Greenhouse Diameter 2023.csv** - contains all measurements of seedling stem diameter recorded during the 2022 'treatment year' and the 2023 'recovery year.' During each measurement campaign, each seedling was measured at two perpendicular points on the stem 3 cm from the soil surface and these measurements were averaged into a single value. Columns are as follows: Date: in mm/dd/yyyy format, the date on which diameter measurement was recorded in 2022 or 2023. Measurement.round: unique number of measurement iteration, 1-7. Because a round of measurements was sometimes done over a period of two days, we assigned a single measurement round number to each iteration of measurements. Rounds 1-6 were recorded across the treatment period in 2022, while round 7 was recorded at the end of the 'recovery year' in autumn 2023. Tree.ID: unique ID number associated with a single seedling. Seedlings planted together in one container each had a unique ID number. ID numbers were assigned upon planting. Any missing ID numbers were seedlings removed prior to the beginning of the experiment. species: seedling species. piru =* Picea rubens* (red spruce), quru =* Quercus rubra* (northern red oak), bepa =* Betula papyrifera* (paper birch) drought treatment: one of three drought treatment levels, assigned to each container. long = long drought (30 days water reduction); short = short drought (15 days water reduction); irrigated = no water reduction, container irrigated to field capacity. N/A values indicate this seedling was measured as an 'extra' control but was not assigned an experimental treatment. warm treatment: one of two warming treatment levels assigned to each container, by half-block. heat = 15-day passive warming, ambient = no warming, ambient greenhouse temperatures throughout. N/A values indicate this seedling was measured as an 'extra' control but was not assigned an experimental treatment.  avg.diam.mm: average of two stem diameter measurements taken 3 cm from soil surface, in millimeters. **Greenhouse Height 2022.csv** - contains all measurements of seedling stem diameter recorded during the 2022 'treatment year.' During each measurement campaign, each seedling was measured from the base of the stem at the soil surface to the growing tip of the longest living shoot. Columns are as follows: Tree.ID: unique ID number associated with a single seedling. Seedlings planted together in one container each had a unique ID number. ID numbers were assigned upon planting. Any missing ID numbers were seedlings removed prior to the beginning of the experiment. Measurement.round: unique number of measurement iteration, 1-6. Because a round of measurements was sometimes done over a period of two days, we assigned a single measurement round number to each iteration of measurements. species: seedling species. piru = *Picea rubens (red spruce), quru =* Quercus rubra (northern red oak), bepa =* Betula papyrifera* (paper birch) drought treatment: one of three drought treatment levels, assigned to each container. long = long drought (30 days water reduction); short = short drought (15 days water reduction); irrigated = no water reduction, container irrigated to field capacity warm treatment: one of two warming treatment levels assigned to each container, by half-block. heat = 15-day passive warming, ambient = no warming, ambient greenhouse temperatures throughout  height.cm: height of an individual seedling from the base of the stem at the soil surface to the growing tip of the longest living shoot, in centimeters. doy: day of year that the measurement was taken in 2022. height.start: height of each seedling at first measurement (beginning of 2022 season). This value should equal height.cm at Measurement.round 1. rel.height: a percentage value indicating a percent change in seedling height relative to starting height.  competition: one of six competition treatment levels, assigned to individual seedlings. single = planted alone; comp-piru = planted with a spruce seedling; comp-quru = planted with an oak seedling; comp-bepa = planted with a birch seedling block: ID number of experimental block, 1-4. half.block: ID of experimental half-block, each half of an experimental block assigned to either a warming treatment or no warming. Format is treatment_block ID. **Greenhouse Height 2023.csv** - contains all measurements of seedling height recorded during the 2022 'treatment year' and the 2023 'recovery year.' During each measurement campaign, each seedling was measured from the base of the stem at the soil surface to the growing tip of the longest living shoot. Columns are as follows: Date: in mm/dd/yyyy format, the date on which height measurement was recorded in 2022 or 2023. Measurement.round: unique number of measurement iteration, 1-7. Because a round of measurements was sometimes done over a period of two days, we assigned a single measurement round number to each iteration of measurements. Rounds 1-6 were recorded across the treatment period in 2022, while round 7 was recorded at the end of the 'recovery year' in autumn 2023. Tree.ID: unique ID number associated with a single seedling. Seedlings planted together in one container each had a unique ID number. ID numbers were assigned upon planting. Any missing ID numbers were seedlings removed prior to the beginning of the experiment. species: seedling species. piru = *Picea rubens* (red spruce), quru = *Quercus rubra* (northern red oak), bepa = *Betula papyrifera* (paper birch) drought treatment: one of three drought treatment levels, assigned to each container. long = long drought (30 days water reduction); short = short drought (15 days water reduction); irrigated = no water reduction, container irrigated to field capacity. N/A values indicate this seedling was measured as an 'extra' control but was not assigned an experimental treatment. warm treatment: one of two warming treatment levels assigned to each container, by half-block. heat = 15-day passive warming, ambient = no warming, ambient greenhouse temperatures throughout. N/A values indicate this seedling was measured as an 'extra' control but was not assigned an experimental treatment. height.cm: height of an individual seedling from the base of the stem at the soil surface to the growing tip of the longest living shoot, in centimeters. Missing values indicate the seedling died in 2022 and was not used in 2023 analysis. **Chamber Climate_2022.csv** - a file of climate conditions in experimental warming and control chambers recorded during the 2022 'treatment year,' including temperature, relative humidity, saturated vapor pressure, and vapor pressure deficit. Temperature and relative humidity were logged automatically every 15 minutes on climate dataloggers (DS1923-F5# Hygrochron, iButtonLink LLC, Whitewater, WI) and averaged to 2-hour values. Columns are as follows: doy: day of year that the measurement was taken in 2022. Temp: 2-hour average of temperature values (in Celsius) that were logged every 15 minutes. RH: 2-hour average of relative humidity values (in %) that were logged every 15 minutes. RH.corr: 'corr' indicates an RH value that was automatically logged as &gt;100% (artifact of very high humidity), manually corrected during data cleaning to 100. 'NA' values indicate this RH value was not manually corrected. SVP: saturated vapor pressure. VPD: vapor pressure deficit calculated from 2-hour averages of temperature and humidity, in kPa. block: ID number of experimental block, 1-4. warm treatment: one of two warming treatment levels assigned to each container, by half-block. heat = 15-day passive warming, ambient = no warming, ambient greenhouse temperatures throughout. N/A values indicate this seedling was measured as an 'extra' control but was not assigned an experimental treatment. half.block: ID of experimental half-block, each half of an experimental block assigned to either a warming treatment or no warming. Each half-block chamber (fully covered in clear siding for warming treatment, open sided for control) contained a hygrochron datalogger. Format is treatment_block ID. **Chamber Climate Wide Form_2022.csv** - wide format 2022 climate data for group testing, with an individual column for each climate variable in each warming treatment level, recorded during and after warming treatment. Columns are as follows: doy: day of year that the measurement was taken in 2022. block: ID number of experimental block, 1-4. hw: indicates whether value was recorded pre-, during, or post-warming treatment, allowing for categorical testing among treatment timing for all treatment levels. prhw = pre warming treatment (experiment start date until warming treatment start date); hw = during warming treatment (warming treatment start date to warming treatment end date); phw = post warming treatment (warming treatment end date to experiment end date). Temp.warm: temperature in each warmed half-block, recorded every 15 minutes and averaged across 2 hours (Celsius). VPD.warm: vapor pressure deficit in each warmed half-block, based on temperature and humidity recorded every 15 minutes and averaged across 2 hours (kPa). RH.warm: relative humidity in each warmed half-block, recorded every 15 minutes and averaged across 2 hours (kPa). Temp.amb: temperature in each control (ambient temperature) half-block, recorded every 15 minutes and averaged across 2 hours (Celsius). VPD.amb: vapor pressure deficit in each control half-block, based on temperature and humidity recorded every 15 minutes and averaged across 2 hours (kPa). RH.amb: relative humidity in each control half-block, recorded every 15 minutes and averaged across 2 hours (kPa). **gs90 Log_2022.csv** - file of all stomatal conductance (gs) values recorded using LI-6400 (LI-COR Environmental, Lincoln, NE) and corresponding water potential values used to model and calculate species-level values of gs90 (water potential at 90% stomatal closure). Columns are as follows: Date: in mm/dd/yyyy format, the date on which gs and water potential measurements were recorded in 2022. Tree.ID: unique ID number associated with a single seedling. Seedlings planted together in one container each had a unique ID number. ID numbers were assigned upon planting. Any missing ID numbers were seedlings removed prior to the beginning of the experiment. species: seedling species. piru = *Picea rubens* (red spruce), quru = *Quercus rubra* (northern red oak), bepa = *Betula papyrifera* (paper birch) Treatment: either drought treatment or irrigated, not split into long or short drought as water potential and soil moisture values were used as continuous variables to describe water stress for this analysis rather than splitting categorically by treatment. Values of 'extra' indicate that the seedling was either an extra seedling outside the experimental blocks and unassigned to a treatment, or treatment was not indicated at the time of measurement as it was not used as an explanatory variable.  gs log 1-5: individual measurements of gs (mol m-2 s-1) on an individual seedling and leaf recorded by LI-6400 during sampling. gs average: value of gs on an individual seedling and leaf averaged across 5 recorded measurements. wp 1-3: values of water potential (MPa) of leaf tissue recorded by thermocouple psychrometer upon sample equilibration. Leaf tissue samples were taken from the same leaf on which gs measurements were performed. Water Potential MPa: value of water potential (MPa) averaged across 3 recorded measurements for a single leaf tissue sample. soil moisture 1: first value of VWC in a single container, containing the sampled seedling. 'NA' values indicate that soil moisture was not measured during this sampling campaign, as it was not an explanatory variable. soil moisture 2: second value of VWC in the same container, measured across the container from the first measurement. 'NA' values indicate that soil moisture was not measured during this sampling campaign, as it was not an explanatory variable. soil moisture avg: average of percent sm 1 and 2. 'NA' values indicate that soil moisture was not measured during this sampling campaign, as it was not an explanatory variable. **gs90fulldata_2022.csv** - file of average gs and water potential measurements in 2022 used to model gs90 as well as concurrent climate and environmental measurements. Essentially a summarized version of the above gs90 file but including environmental variables. Both files are used in analysis script. Columns are as follows: Date: in mm/dd/yyyy format, the date on which gs and water potential measurements were recorded in 2022. Tree.ID: unique ID number associated with a single seedling. Seedlings planted together in one container each had a unique ID number. ID numbers were assigned upon planting. Any missing ID numbers were seedlings removed prior to the beginning of the experiment. species: seedling species. piru = *Picea rubens* (red spruce), quru = *Quercus rubra* (northern red oak), bepa = *Betula papyrifera* (paper birch) Treatment: either drought treatment or irrigated, not split into long or short drought as water potential and soil moisture values were used as continuous variables to describe water stress for this analysis rather than splitting categorically by treatment. Values of 'extra' indicate that the seedling was either an extra seedling outside the experimental blocks and unassigned to a treatment, or treatment was not indicated at the time of measurement as it was not used as an explanatory variable.  gs average: value of gs on an individual seedling and leaf averaged across 5 recorded measurements. Water Potential MPa: value of water potential (MPa) averaged across 3 recorded measurements for a single leaf tissue sample. Temp licor: temperature (Celsius) as recorded by LI-6400 internal thermometer (LI-COR Environmental, Lincoln, NE) during gs measurement VPD licor: vapor pressure deficit (kPa) as recorded by LI-6400 during gs measurement Soil moisture: average of two container media moisture values in the seedling's container (%) Timestamp: 24-hour formatted time of measurement (EST) as recorded by LI-6400. **Temp Response Full.csv** - a file of all gas exchange and climate variable measurements recorded for analysis of photosynthetic temperature and moisture response of seedlings. Gas exchange measurements including maximum light-adapted photosynthesis measured using LI-6400 fitted with either a standard cuvette or an RGB conifer chamber (LI-COR Environmental, Lincoln, NE). Columns are as follows: Tree.ID: unique ID number associated with a single seedling. Seedlings planted together in one container each had a unique ID number. ID numbers were assigned upon planting. Any missing ID numbers were seedlings removed prior to the beginning of the experiment. species: seedling species. piru = *Picea rubens* (red spruce), quru = *Quercus rubra* (northern red oak), bepa = *Betula papyrifera* (paper birch) drought treatment: one of three drought treatment levels, assigned to each container. long = long drought (30 days water reduction); short = short drought (15 days water reduction); irrigated = no water reduction, container irrigated to field capacity. Photo: average of 5 recorded values of photosynthetic rate (mmol CO2 m-2 s-1) on a single leaf of an individual seedling. Cond: average of 5 recorded values of stomatal conductance to water vapor (mol m-2 s-1) on a single leaf of an individual seedling. Temp_leaf: temperature of leaf in sample cuvette/chamber (Celsius) as recorded by LI-6400. RH_s: relative humidity in sample cuvette/chamber (%) as recorded by LI-6400. Soil.moisture: average of two container media moisture values in the seedling's container (%) VPD.s: vapor pressure deficit (kPa) in sample cuvette/chamber as recorded by LI-6400. doy: day of year in 2022 on which measurement was recorded. **growth phys_2022-2023.csv** - file of leaf water potential and relative growth values used for analysis of the relationship between leaf turgor loss during drought in treatment year 2022 and magnitude of seasonal growth in 2022. Measurements were performed on a randomly selected sample of seedlings in each drought treatment. For analysis of growth at the end of the 2023 season, 2023 height and diameter datasets were pulled in RStudio and merged with the current dataframe, using the same end-of-treatment water potential values. Columns are as follows: tree.ID: unique ID number associated with a single seedling. Seedlings planted together in one container each had a unique ID number. ID numbers were assigned upon planting. drought treatment: either drought (long or short) or irrigated, not split into long or short drought within this variable warm treatment: one of two warming treatment levels assigned to each container, by half-block. heat = 15-day passive warming, ambient = no warming, ambient greenhouse temperatures throughout.  drought.length: one of three drought treatment levels, assigned to each container. long = long drought (30 days water reduction); short = short drought (15 days water reduction); irrigated = no water reduction, container irrigated to field capacity. Avg.Water.Potential: value of water potential (MPa) measured at the end of each respective drought treatment, averaged across 3 recorded measurements for a single leaf tissue sample. Avg.soil.moisture: average of two container media moisture measurements in the seedling's container, measured upon sampling leaf tissue for water potential measurement doy.wp: day of year in 2022 (day on which treatment was ended) on which leaf tissue was sampled and leaf water potential measurement was recorded. Because these water potential values were sampled at the end of each drought treatment level, the value in this column should be either 197 or 214. rel.height.eos: relative height (percent change relative to start-of-season height) at the end of the 2022 growing season (September) block: ID number of experimental block, 1-4. half.block: ID of experimental half-block, each half of an experimental block assigned to either a warming treatment or no warming. Format is treatment_block ID. doy.htdm: day of year in 2022, after the end of the growing season, on which height and diameter measurements were performed. This should be 273 for all measurements in 2022. rel.diam.eos: relative diameter (percent change relative to start-of-season diameter) at the end of the 2022 growing season (September) species: seedling species. piru = *Picea rubens* (red spruce), quru = *Quercus rubra* (northern red oak), bepa = *Betula papyrifera* (paper birch) tlp: species-level osmotic potential at turgor loss (turgor loss point, TLP, MPa), used to calculate the difference between species turgor loss point and individual leaf tissue water potential at the end of each drought treatment (psi diff). psi diff: the difference between 2022 end-of-treatment leaf water potential of an individual seedling and its species-level turgor loss point (MPa). Modeled during analysis as explanatory variable against end-of-season relative height and diameter in 2022 and 2023 **Greenhouse Vigor 2023.csv** - file of visual assessment of seedlings' vigor, measured as estimate of percent brown foliage to the nearest 5%. Vigor assessment data were also used to determine seedling mortality. Columns are as follows: Date: in mm/dd/yyyy format, the date on which vigor measurement was recorded in 2022 or 2023. Measurement.round: unique number of measurement iteration, 1-7. Because a round of measurements was sometimes done over a period of two days, we assigned a single measurement round number to each iteration of measurements. Rounds 1-6 were recorded across the treatment period in 2022, while round 7 was recorded at the end of the 'recovery year' in autumn 2023. Tree.ID: unique ID number associated with a single seedling. Seedlings planted together in one container each had a unique ID number. ID numbers were assigned upon planting. Any missing ID numbers were seedlings removed prior to the beginning of the experiment. species: seedling species. piru = *Picea rubens* (red spruce), quru = *Quercus rubra* (northern red oak), bepa = *Betula papyrifera* (paper birch) drought treatment: one of three drought treatment levels, assigned to each container. long = long drought (30 days water reduction); short = short drought (15 days water reduction); irrigated = no water reduction, container irrigated to field capacity. N/A values indicate this seedling was measured as an 'extra' control but was not assigned an experimental treatment. warm treatment: one of two warming treatment levels assigned to each container, by half-block. heat = 15-day passive warming, ambient = no warming, ambient greenhouse temperatures throughout. N/A values indicate this seedling was measured as an 'extra' control but was not assigned an experimental treatment. Percent brown foliage: visual assessment of brown foliage on an entire individual, as a percent of 100 rounded to the nearest 5%. Percent green foliage: 100 - percent brown foliage Notes: any additional comments on seedling health, appearance, etc. **Gmin final data_2022.csv** - table of species and calculated minimum epidermal conductance (gmin) for 27 individuals. gmin was determined using the methodology and calculation sheets developed by Sack and Scoffoni (2011). Values of gmin were then transferred to this file for visualization and analysis. Columns are as follows: Species: species of each individual sampled. Red spruce, Red oak, Paper birch. Consecutive species names indicate two samples from the same individual seedling. gmin: calculated minimum epidermal conductance (mmol m-2 s-1) for each sample. **Water Potential Soil Moisture_2022.csv** - file of all leaf water potential and soil moisture survey measurements recorded during the 2022 'treatment year' growing season, used for all analysis and visualization involving water potential measurements (other than growth-water potential analysis, which is a separate file that only includes end-of-treatment water potential measurements). Water potential tissue samples were measured at least once a week for the duration of the drought treatment. Columns are as follows: Date: in mm/dd/yyyy format, the date on which leaf water potential and concurrent soil moisture measurement were performed in 2022. species: seedling species. piru = *Picea rubens* (red spruce), quru = *Quercus rubra* (northern red oak), bepa = *Betula papyrifera* (paper birch) drought treatment: either drought (long or short) or irrigated, not split into long or short drought within this variable warm treatment: one of two warming treatment levels assigned to each container, by half-block. heat = 15-day passive warming, amb = no warming, ambient greenhouse temperatures throughout.  drought.length: one of three drought treatment levels, assigned to each container. long = long drought (30 days water reduction); short = short drought (15 days water reduction); irrigated = no water reduction, container irrigated to field capacity. competition: competition treatment not split out into six treatments, only indicating whether a seedling was single or planted in competition (comp) with another seedling avg.water.potential: value of leaf water potential (MPa) averaged across 3 recorded measurements for a single leaf tissue sample taken on a given day. avg.sm: value of container media moisture (% volumetric water content), averaged between two moisture readings on opposite sides of the container notes: additional observations, anomalies in sample or measurement, noted errors doy: day of year in 2022 on which the measurement was taken. tree.ID: unique ID number associated with a single seedling. Seedlings planted together in one container each had a unique ID number. ID numbers were assigned upon planting. Seedlings were randomly selected from each drought treatment level for leaf water potential sampling. **TLP_combined.csv** - file of species-level values of osmotic potential at turgor loss (turgor loss point, TLP, MPa), calculated using control seedlings in 2022. Columns are as follows: Date: in mm/dd/yyyy format, the date on which leaf tissue samples were used for determination of turgor loss point using the rapid osmometer method developed by Bartlett et al. (2012) species: seedling species. piru = *Picea rubens* (red spruce), quru = *Quercus rubra* (northern red oak), bepa = *Betula papyrifera* (paper birch) sample ID: unique ID of each tissue sample from an individual leaf. When one leaf was sampled (two tissue samples per leaf, placed in the same chamber for measurement), the sample ID corresponds to the seedling ID. When two leaves were sampled from the same seedling, the sample ID indicates leaves A and B from one seedling. tlp sample: the turgor loss point value (MPa) calculated using Bartlett et al. (2012)'s model, based on the water potential of a single tissue sample on a single date. tlp tree: the average of all values calculated from a single seedling on a single date. tlp species: the average of all values calculated from one species on a single date. avg tlp species: the average of all values of turgor loss point calculated for one species on all sampling dates. These values were used in analysis and comparison of turgor loss point to midday water potential values.