DOI: 10.7280/d10m6s
title: Data for: Long-term drought reduces wildfire severity and promotes invasive species

description: Anthropogenic climate change has increased the frequency of extreme
 drought, wildfires, and invasions of non-native species. Studying
 interactions amongst these multiple stressors is rarely done at the local
 scale yet is key to anticipating impacts on vulnerable ecosystems. We
 leveraged an existing experimental rainfall manipulation to evaluate the
 relationship between precipitation, fuel load, and fire severity in a
 Southern California coastal sage scrub system. We asked whether pre-fire
 rainfall manipulation influenced fuel load and vegetation cover with
 consequences for fire severity and post-fire community composition. We
 measured plant biomass and community composition before and after the 2020
 Santiago wildfire in experimental plots with three rainfall treatments.
 After fire, we measured number of branches, diameter of the smallest
 terminal branch, leaf percent cover, and height on three dominant native
 shrub species (Malosma laurina, Artemisia californica, and Salvia
 mellifera) to assess fire severity. Native shrubs had greater pre-fire
 cover in added water plots compared to reduced water plots. Experimental
 drought led to less fuel build-up, less native shrub cover, and more
 invasive grass cover. The decreased biomass led to lower fire severity
 indicated by smaller branch diameters and more terminal branches after
 burning. Post-fire shrub cover was low in all plots, and lowest in added
 and ambient plots compared to reduced water plots. There were fewer native
 and more invasive species in post-fire droughted plots compared to
 post-fire irrigated and ambient water plots. Our results demonstrate the
 importance of fuel load to fire severity and plant community composition
 on an ecosystem scale. Management strategies should focus on reducing fire
 frequency to maintain the resilience of coastal sage scrub communities
 facing drought. Control burns are not recommended for coastal sage scrub
 communities because they will promote the growth of non-native plants.
description: The Loma Ridge manipulation consists of replicate experimental
 blocks established in CSS and grassland communities. Each experimental
 block includes 6 plots, with each plot randomly assigned to a unique water
 (droughted, ambient, and added) and nitrogen (ambient or added)
 manipulation treatment. The drought involves an approximately 40%
 reduction in precipitation, achieved by covering plots with plastic during
 large storms. Water is funneled into storage tanks and is later pumped on
 water addition plots that receive approximately 30% more water through
 irrigation lines. To measure plant community
 composition, each plot was divided into three 4x4m quadrats, within which
 all species were identified and % cover was visually estimated. For all
 shrubs, separate cover values were recorded for crown-sprouting
 individuals, dead shrubs, and seedlings. Overlapping plants meant that
 plant cover could total &gt;100%. Ground cover values (bare ground,
 thatch, litter, cryptobiotic crust, rock, or moss) were separately
 estimated so that they totaled 100%. We collected
 herbaceous biomass and litter within four 14 cm by 50 cm sampling frames
 per plot each April. Within each of these frames, the cover of any rooted
 plants, along with ground cover, was recorded by functional group (forbs,
 grasses, shrubs, litter, or bare ground) to total 100%. It was extremely
 rare for shrubs to be rooted within this small frame, so shrub cover was
 typically close to 0%. After estimating cover, all litter within each
 frame was collected and all herbaceous material was cut and harvested.
 Material was dried in an oven at 60°C degrees for 4 days and weighed. The
 herbaceous mass measurements include separate and combined totals of all
 living biomass and dead (litter) mass within each sampling frame. Shrub
 biomass was estimated pre-fire by measuring all shrubs greater than 20 cm
 in height that were rooted within the 4x4 m subplot. Total height (H,
 height at the tallest point), width 1 (W1, width at the widest point) and
 width 2 (W2, width perpendicular to width1) were used to estimate total
 shrub volume (V=H*pi(W1*W2/4)). Biomass was estimated from volume using
 regression equations developed for each species or generalized shrub
 regression equations (Vourlitis and Pasquini 2009).
 After fire in Spring 2021, impacts of fire severity on CSS were
 measured in each of the 24 subplots representing added, ambient, and
 reduced precipitation with ambient nitrogen. We measured three individuals
 of each of the three most abundant species <em>(Malosma
 laurina</em>, <em>Artemisia californica</em>, and
 <em>Salvia mellifera</em>) in each plot. For each individual
 shrub, we counted the number of branches remaining, the percentage of
 branches with leaves, the diameter of the smallest terminal branch (branch
 width), the height of the burned shrub, the number of burned shrubs that
 were crown sprouting, and the height of the basal crown sprouting new
 growth. Higher fire severity results in lower branch count and leaf
 percent cover, and greater branch thickness (Perez and Moreno
 1998).
description: # Reference Information ## Provenance for this README * File name:
 README_Dataset-FireSeverity_v0.1.0.txt * Author: Sarah Kimball * Other
 contributors: Jessica Rath, Julie Coffey, Moises Perea-Vega, Matthew
 Walsh, Nicole M. Fiori, Priscilla Ta, Katharina T. Schmidt, Michael L.
 Goulden, and Steven D. Allison * Date created: 2023-12-21 * Date modified:
 2024-01-05 ## Dataset Version and Release History * Current Version: *
 Number: 1.0.0 * Date: 2024-01-05 * Persistent identifier: DOI: * Summary
 of changes: n/a * Embargo Provenance: n/a * Scope of embargo: n/a *
 Embargo period: n/a ## Dataset Attribution and Usage * Dataset Title: Data
 for the article "Long-term drought promotes invasive species by
 reducing wildfire severity" * Persistent Identifier: * Dataset
 Contributors: * Creators: Sarah Kimball, Jessica Rath, Julie Coffey,
 Moises Perea-Vega, Matthew Walsh, Nicole M. Fiori, Priscilla Ta, Katharina
 T. Schmidt, Michael L. Goulden, and Steven D. Allison * Date of Issue: *
 Publisher: * License: Use of these data is covered by the following
 license: * Title: CC0 1.0 Universal (CC0 1.0) * Specification:
 ; the authors
 respectfully request to be contacted by researchers interested in the
 re-use of these data so that the possibility of collaboration can be
 discussed. ## Contact Information * Name: Sarah Kimball * Affiliations:
 Department of Ecology and Evolutionary Biology, University of California,
 Irvine, CA 92697 * ORCID ID: 
 * Email: --- # Additional Dataset Metadata ##
 Dates and Locations * Dates of data collection: Field data collected
 between March 2020 and September 2021 * Geographic location of data
 collection: Fieldwork conducted at the Loma Ridge Global Change Experiment
 in the foothills of the Santa Ana Mountains, Orange County, CA, USA (see
 publication for more details) --- # Methodological Information * Methods
 of data collection/generation: see manuscript for details --- # Data and
 File Overview ## Summary Metrics * File count: 6 * Total file size: 250 KB
 * Range of individual file sizes: 534 bytes - 2 KB * File formats: .csv ##
 Table of Contents * BothYearsCommComp.csv * HerbBiomass.csv *
 LivingShrubs.csv * LomaFireSeverity_Individuals_AmbientN.csv *
 Shrub2020Biomass.csv * Survivorship.csv # File Details ## Details for:
 BothYearsCommComp.csv * Description: a comma-delimited file containing two
 years of plant community composition data from ambient Nitrogen plots
 within the Loma Ridge Global Change Experiment. Data are from 2020 (before
 wildfire) and 2021 (after wildfire). * Format(s): .csv * Size(s): 2 KB *
 Dimensions: 25 rows x 22 columns * Variables: * Year: calendar year in
 which data were collected * Plot_ID: unique plot identification
 information; CSS = coastal sage scrub; number = plot number; first letter
 L or R - left or right side of plot; second letter refers to water
 treatment where R=reduced water, A=added water, X=ambient water; third
 letter refers to nitrogen treatment, where X=ambient nitrogen. *
 Treatment: water treatment * Columns D through V: percent cover of
 different functional groups, ground cover categories, or focal species; *
 ShrubsELYCON: total percent cover of all native shrubs and the large
 native grass Elymus condensatus; * NativeShrubs: total percent cover of
 all native shrubs; * NativeForbs: total percent cover of all native forbs;
 * NNForbs: cover of all non-native forbs; * StipaSpp: cover of the native
 bunchgrasses in the genus * Stipa; NNGrass: cover of all non-native
 grasses; * AllPlants: combined cover of all plants; * Bare: bare ground; *
 LitterThatch: litter and thatch; * F: fine woody debris: L: litter; * M:
 moss; * R: rock; * S: stem; * TH: thatch; * W: coarse woody debris; *
 artcal: Artemisia californica; * salmel: Salvia mellifera; * mallau:
 Malosma laurina ## Details for: HerbBiomass.csv * Description: a
 comma-delimited file containing the herbaceous biomass data collected from
 plots before and after wildfire. * Format(s): .csv * Size(s): 1 KB *
 Dimensions: 25 rows x 12 columns * Variables: * Year: calendar year in
 which data were collected * Treatment: water treatment * Plot: unique plot
 number, left or right side of plot, water treatment, and nitrogen
 treatment * Columns D through F: percent cover of functional groups in
 biomass plots * HerbaceousMass: weight in grams of all above-ground
 herbaceous biomass * Columns H through K: percent cover of ground cover
 types * LitterMass: weight in grams of all plant litter in the biomass
 plot ## Details for: LivingShrubs.csv * Description: a comma-delimited
 file containing the number of individuals of three shrub species that were
 alive in each plot after wildfire. * Format(s): .csv * Size(s): 988 bytes
 * Dimensions: 40 rows x 4 columns * Variables: * Plot: unique plot number,
 left or right side of plot, water treatment, and nitrogen treatment *
 Treatment: water treatment * Species: 6 letter code for species; salmel:
 Salvia mellifera; artcal; Artemisia californica; mallau: Malosma laurina.
 * Count: total number of living individuals found in the plot ## Details
 for: LomaFireSeverity\_Individuals\_AmbientN.csv * Description: a
 comma-delimited file containing measurements of branch diameter, leaves
 remaining, etc. on individual shrubs after the wildfire in each study
 plot. * Format(s): .csv * Size(s): 6 KB * Dimensions: 86 rows x 16 columns
 * Variables: * Page: the numbered raw datasheet * Year: calendar year of
 measurement * Date: Date of measurement * Team: initials of researchers
 who collected data * Plot_Number: number of study plot * Position: side of
 plot. L=left; R=right * Water_Treatment: added, ambient, or reduced *
 Nitrogen_Treatment: ambient * Plot_ID: full plot name * Species: 6 letter
 code for species; salmel: Salvia mellifera; artcal; Artemisia californica;
 mallau: Malosma laurina. * Individual: number of individual shrub *
 TotHeight: height of individual in cm * CSHeight: height of
 crown-sprouting portion of shrub in cm * Branch_Count: number of branches
 * PercentLeaf: percentage of branches with leaves * AvgDiameter: terminal
 diameter of an averaged-sized branch in cm * Missing data codes:
 "NA" is entered for missing data ## Details for:
 Shrub2020Biomass.csv * Description: a comma-delimited file containing
 measurements of shrubs and formulas used to estimate biomass prior to the
 wildfire. * Format(s): .csv * Size(s): 23 KB * Dimensions: 166 rows x 18
 columns * Variables: * Plot: plot identification number * Treatment: water
 treatment * Species: 6 letter code for species; salmel: Salvia mellifera;
 artcal; Artemisia californica; mallau: Malosma laurina. * Live_Or_Dead:
 whether the shrub was living or dead at time of measurement * Height_cm:
 shrub height in cm * Width_cm: shrub width at the widest point in cm *
 Width2_cm: shrub width at a 90 degree angle from first width measurement
 in cm * sq volume: height x width x width2 * a: parameter from equation to
 estimate shrub volume from measurements (y=ax+b) described in the Methods
 section of the paper * b: parameter from equation to estimate shrub volume
 from measurements (y=ax+b) described in the Methods section of the paper *
 ln_biomass: natural log of estimated biomass * biomass_g: estimated
 biomass in grams * r: shrub radius, calculated as (width + width2)/2 *
 circ volume: estimated shrub volume assuming a cylinder (cm3) * ln volume:
 natural log of estimated volume * Notes: field notes on shrub health and
 condition * Area_m2: the estimated area of the base of the shrub *
 biomass_g_per_m2: results from estimated biomass equations ## Details for:
 Survivorship.csv * Description: a comma-delimited file containing the
 number of living and dead individuals in each plot. * Format(s): .csv *
 Size(s): 534 bytes * Dimensions: 14 rows x 8 columns * Variables: *
 Plot_ID: plot identification * salmel: number of living Salvia mellifera *
 artcal: number of living Artemisia californica * mallau: number of living
 Malosma laurina * Dead: number of dead shrubs in each plot *
 TotalLivingDead:total number of all living and dead shrubs in each plot *
 PercentAlive: percentage of living shrubs in each plot * Treatment: water
 treatment --- END OF README