Data for: Long-term drought reduces wildfire severity and promotes invasive species
Data files
Jan 08, 2024 version files 43.43 KB
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BothYearsCommComp.csv
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HerbBiomass.csv
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LivingShrubs.csv
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LomaFireSeverity_Individuals_AmbientN.csv
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README.md
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Shrub2020Biomass.csv
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Survivorship.csv
Abstract
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.
README: 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: https://creativecommons.org/publicdomain/zero/1.0/; 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: https://orcid.org/0000-0003-3789-4741
- Email: skimball@uci.edu
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
Methods
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 >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 (Malosma laurina, Artemisia californica, and Salvia mellifera) 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).