Evaluating immaturity risk in young stands of the serotinous knobcone pine (Pinus attenuata)
Data files
Jan 16, 2024 version files 91.19 KB
Abstract
As wildfire becomes increasingly frequent, many plant populations risk local extirpation if fire recurs too soon, a problem dubbed “immaturity risk”. We studied the regeneration of a serotinous conifer species, knobcone pine (Pinus attenuata), as a function of the time between high-severity fires (6-79 years). We evaluated age, cone production, and regeneration at two burned sites in northern California, the Ranch Fire (2018) in Mendocino National Forest, and the Carr Fire (2018) in Whiskeytown National Recreation Area. We found an average of 30.5 filled seeds in closed, brown cones (42% viability of filled seeds). The bulk of the older (gray) cones were partially or fully open, and thus available seed in them at the time of fire was approximately halved. Adjusting for survivorship, the estimated minimum age for knobcone pine to produce one recruit per tree (self-replacement) was 8.2 years. Characterizing the probability of burning as a negative exponential model and using an 81-year return time, we found the likelihood of reburn before 8.2 years was 0.09. Our study demonstrated the importance of understanding the size and time to reproductive maturity in serotinous tree species to adequately quantify immaturity risk. Based on our results and current estimates of return time, we suggested that immaturity risk is very low for knobcone pine. Our approach could be broadly applied to better quantify immaturity risk in other conifer species.
README: Evaluating immaturity risk in young stands of the serotinous knobcone pine (Pinus attenuata)
https://doi.org/10.5061/dryad.x3ffbg7k8
Abstract
For most statistical analyses, we used a linear regression model approach in R (R Development Core Team 2020) with log transformed variables when necessary to meet assumptions of normality and equal variance. We adopted the cumulative negative exponential model to evaluate immaturity risk in knobcone pine (Equation 1). To calculate the probability of reburning before age (F(t)), we separately used the modern mean fire cycle and potential historical fire cycle (RT), for the entire range of knobcone pine in northern California and southern Oregon.
To estimate the modern fire rotation for knobcone pine, we acquired perimeters of all fires >400 ha occurring between 1984 and 2021 from the Monitoring Trends in Burn Severity (MTBS) program (www.mtbs.com; Eidenshink et al., 2007) and clipped them to the range of knobcone pine as mapped by E.L. Little’s “Atlas of United States Trees” (USGS 1999). We used the fire perimeter data to calculate the fire rotation for the 25-year period preceding each year from 2009 to 2021 following Reilly et al. (2019). Fire rotation was calculated as the 25-year time period divided by the proportion of the total range of knobcone pine that burned during that time period. We then used the inverse of the fire rotation as the single parameter in the negative exponential fire cycle (Johnson 1996).
Usage notes
These datasets were collected in Whiskeytown National Recreation Area and Mendocino National Forest 2019-2021.
Details for each dataset are provided in the README file.
Datasets included:
- Knobcone
- Data collected on trees and cones from Whiskeytown and Mendocino
- Fire = Whiskeytown or Mendocino
- Age = average age of trees within 5-15 square meters radius
- DBH = average DBH in millimeters
- DBHcm = DBH in centimeters
- rgn = number of recruits within 5-15 square meters radius
- rpm = number of recruits per 5-15 square meters radius
- rrpm = number of recruits per 5-15 square meters radius, adjusted for survivorship
- lrpm = log of rrpm
- rpt = number of recruits within 5-15 square meters radius per number of trees within 15 square meters radius
- gcones = number of cones on the ground within 5-15 square meters radius for Whiskeytown, with no values for Mendocino (cones in trees and on ground were not differentiated at this location). Therefore these cells are filled with n/a.
- rrpt = number of recruits within 5-15 square meters radius per number of trees within 15 square meters radius, adjusted for survivorship
- tcon = cones in trees within 5-15 square meters radius for Whiskeytown, or all cones within 15 square meters for Mendocino
- cpm = total cones per 5-15 square meters radius for Whiskeytown and Mendocino
- lcpm = log total cones per 5-15 square meters radius
- rpc = number of recruits per number of cones within 5-15 square meters radius
- cpt = total number of cones per number of trees within 5-15 square meters radius
- lcpt = log total number of cones per number of trees within 5-15 square meters radius
- trees = number of trees within 5-15 square meters radius
- dens = number of trees per 5-15 square meters radius
- tall = average height of trees within 5-15 square meters radius
- PIAT 25 Yr Fire Rotation
- Year, sum of burn area (ha), and percent (the 25-year time period divided by the proportion of the total range of knobcone pine that burned during that time period)
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