High fire frequency in California chaparral reduces post-fire shrub regeneration and native plant diversity
Data files
Dec 03, 2024 version files 216.01 KB
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LNU_plot_description.csv
8.43 KB
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LNU_severity.csv
805 B
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README.md
6.47 KB
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shrub_height.csv
24.90 KB
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shrub_seedling_data.csv
43.70 KB
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SpeciesList.csv
12.82 KB
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Subplot_species.csv
118.89 KB
Abstract
Fire is crucial for maintaining species diversity and resilience in fire-adapted shrublands of the world’s Mediterranean climate zones (MCZs), which include the chaparral shrublands of the North American MCZ. Chaparral is adapted to high intensity burning, with long intervals between fires (30-100 years) typifying undegraded conditions. In much of the range of chaparral, modern fire frequencies are much higher, driven largely by high densities of human ignitions and coincidence between ignitions and severe weather conditions. This change in the fire regime has major implications for biodiversity, leading to exotic invasion, decreased ecosystem services, and potential type conversion of shrubland to grassland dominated by exotic species. We studied the impact of increased fire frequencies on the composition and abundance of herbaceous and woody species in the Interior Coast Range of northern California. Our study area is one of the most frequently burned areas in California, which afforded us the opportunity to investigate higher fire frequencies than heretofore reported in the scientific literature for California. We surveyed fifty-four 250-m2 plots to assess changes in plant community composition and postfire regeneration of chaparral shrubs across a wide range of fire frequencies, including plots that have burned up to six times in the past 30 years. Our findings reveal that short-interval fires significantly reduced post-fire native woody regeneration, with obligate seeding species experiencing a 99% reduction and facultative species showing an 83% reduction in regeneration in the most frequently burned plots. Moreover, the overall marginal effect of one additional short interval fire decreased the proportion of native species cover by 12% and both richness and Shannon diversity by 4%. Consequently, areas with higher fire recurrence supported a more structurally and botanically homogeneous landscape, dominated by a similar group of non-native species.
README: High fire frequency in California chaparral reduces post-fire shrub regeneration and native plant diversity
We surveyed fifty-four 250-m2 plots to assess changes in plant community composition and postfire regeneration of chaparral shrubs across a wide range of fire frequencies, including plots that have burned up to six times in the past 30 years
1) 'LNU_plot_description.csv'
Dataset of all potential covariates used in the models.
Fields are as follows:
- Site: Unique site name. QuailRidge for Quail Ridge UC Natural Reserve (38°30’ N, 122°08’ W), ColdCanyon for Cold Canyon UC Natural Reserve (38°30’ N, 122°06’ W), Bobcat for Bobcat Ranch Audubon Reserve (38°31’ N, 122°04’ W), and CacheCreek for Berryessa Snow Mountain National Monument (38°54’ N, 122°18’ W) and Valley Vista Regional Park (38°54’ N, 122°16’ W)
- PlotID: A unique plot ID for each distinct transect.
- num_burn: The number of prior fires, according to the California Fire Return Interval Departure (FRID) database, that occured after 1990. Since these fire perimeters generally ignore unburned patches within fires that are less than hundreds of acres in size, we used Google Earth historical imagery to examine the landscape for unburned patches after each fire.
- preFireName: Name of fire prior to the LNU lightning complex
- preFireYear: Year of fire prior to the LNU lightning complex
- crrnFRI: The current fire return interval calculated by dividing the number of years in the fire record by the number of fires occuring between 1908 and the current year in a polygon.
- mdnRFRI: (median Percent FRID) A measure of the extent to which contemporary fires (since 1908) are burning at frequencies similar to the frequencies that occurred prior to Euro-american settlement, with the median reference FRI as a basis for comparison.
- mnPFRID: (mean Percent FRID) A measure of the extent to which contemporary fires (since 1908) are burning frequencies similar to the frequencies that occurred prior to Euro-american settlement, with the mean reference FRI as a basis for comparison.
- mCC_FRI: A condition class categorization of the data in the mnPFRID field.
- PFR: "Presettlement Fire Regime." This represents the dominant vegetation type linked to its probable historical fire regime (Van de Water and Safford 2011)
- ppt: Point estimate of annual average precipitation (mm) using 4 km resolution from the PRISM dataset (PRISM Climate Group 2022).
- tmean: Point estimate of annual average temperature (degrees F) using 4 km resolution from the PRISM dataset (PRISM Climate Group 2022).
- elevation: Elevation of plot in meters
- slope: Percent slope of plot in degrees
- aspect: Aspect of plot in degrees
- hli: Heat load index, which uses aspect and slope to account for the amount of solar radiation received (McCune and Keon 2002)
- Distance_km: Distance from coast, measured in km
- TSLF: 'Time Since Last Fire.' This designates the time between the LNU lightning complex and the most recent fire.
- cool_warm_slope: Broad categorization of aspect, with cool slopes representing North and East aspects and warm slopes representing South and West aspects.
2) LNU_severity.csv
- plotID: A unique plot ID for each distinct transect.
- mean_diam_mm: The stem diameter (mm) one centimeter from the terminus of four stems from a chamise individual. One individual was chosen in or adjacent to each quadrat, and five additional individuals were measured at the entire 250m2 transect scale.
3) Subplot_species.csv
- PlotID: A unique plot ID for each distinct transect.
- year: Year of survey.
- spp: Species code, associated with SpeciesList.csv
- seedling_resprout: Either resprout which designates a shrub that resprouted from burl, seedling which designates a shrub that germinated from a seed, or na for herbaceous species
- cover_count: Cover designates a percent cover quantified in each quadrat. Count designates a count of each seedling or resprout in each quadrat.
- Q1: Quadrat 1 of 5
- Q2: Quadrat 2 of 5
- Q3: Quadrat 3 of 5
- Q4: Quadrat 4 of 5
- Q5: Quadrat 5 of 5
4) shrub_seedling_data.csv
- PlotID: A unique plot ID for each distinct transect.
- spp: Species code, associated with SpeciesList.csv
- year: Year of survey.
- sum.count.5m2: Summation of seedling cover in each quadrat, across the entire transect
- presence: Presence/absence of a seedling in each quadrat
5) shrub_height.csv
- PlotID: A unique plot ID for each distinct transect.
- spp: Species code, associated with SpeciesList.csv
- status: D for dead individual or L for live individual
- prefire_ht_m: Height (meters) before LNU lightning complex, measured by skeleton. Values containing null designate cases where the prefire ht was not recorded (survey year 2022).
- postfire_ht_m: Postfire height (meters) of live vegetation after the LNU lightning complex. Values containing na designate instances without live regrowth (status = D).
- diam_largest_stem: Diameter of largest stem (cm). Values containing null designate cases where the diameter was not recorded (survey year 2022).
- year: Year of survey
6) SpeciesList.csv
- spp: Species code, associated with all other files
- Lifeform: Lifeform according to the University of California Jepson Herbarium eFlora (https://ucjeps.berkeley.edu/eflora/) - TR (tree), SH (shrub), FB (forb), GR (graminoid), FERN (fern).
- scientificNameAuthorship: Abbreviated name of person who named plant
- Species: Species. Values containing na designate instances when plant was only identified to genus
- Genus: Genus
- Native_nonnative: Origin of plant (native or nonnative), according to the University of California Jepson Herbarium eFlora (https://ucjeps.berkeley.edu/eflora/). Values containing na designate instances in which origin is unknown
- fac.obl: Fire regeneration strategy according to USDA Forest Service Fire Effects Information System (https://www.feis-crs.org/feis/) - obligate seeder (OS), facultative seeder (FS), or obligate resprouter (OR). Values containing na designate instances in which fire regeneration strategy is unknown.
- subspecies: Subspecies of plant, if applicable. Values containing na designate instances in which subspecies is not applicable